The 4th International Conference
of the System Dynamics Society
1986 – Seville, Spain
The following papers were presented at the conference in parallel and plenary sessions. The original printed proceedings, edited by J. Aracil, J. A. D. Machuca and M. Karsky were printed in hardcopy and distributed at the conference. Below please find the Paper Index for these proceedings, including abstracts. Available papers are Acrobat (.pdf) files and can be read using Acrobat Reader available from adobe.com.
For details about purchasing a copy of the printed proceedings, visit our website System Dynamics Society.
PAPER INDEX – listed alphabetically by first author:
Lessons from System Dynamics Modeling
Jay W. Forrester
Abstract: The power and utility of system dynamics depends on going beyond a model to implications and generalizations that can be drawn from the process of modeling. System dynamics papers too often stop with the description of a model. But to be effective, models should become part of a more persuasive communications process that interacts with people’s mental models, creates new insights, and unifies knowledge. In doing so, modeling can make use of the full range of available information–the mental data base and the written data base, as well as the numerical data base. The last century has been devoted to exploring the frontier of physical science. During the next century the great frontier will be exploring the dynamic nature of social and economic systems.
Session 1: Software Development
The Development of Dysmap2
Abstract: This paper introduces a new implementation of the System Dynamics simulation Language DYSMAP, a current project at Salford University. A short overview of the history, syntax and features of DYSMAP will be given. The new DYSMAP2 system operates as an interpreter. The relative merits of computer interpretation vs. compilation into FORTRAN will be discussed. An outline of the operation of this new portable package (written in FORTRAN77) will include high level descriptions of the parser, run-time interpreter, the interactive environment, dimensional analyser and the optimiser. The performance of the new DYSMAP2 package will be illustrated.
Multifacetted Modelling in System Dynamics
Abstract: We propose a functional design for a software system whose aim is to provide support for an structured methodology of modelling and simulation in System Dynamics. The design follows mainly the ideas of Multifacetted Modelling developed by Zeigler. Our approach has been to give a hierarchical version of DYNAMO and a collection of functions for the handling of simulation elements in an unified system.
SDSE, System Dynamics Software in Education
Abstract: SDSE is a microcomputer based, interactive and integrated system designed to facilitate the teaching and use of System Dynamics in Education. In this way teachers and students without extensive Computer training are able to construct and simulate system models after short period of learning.
System Dynamics has been included in Atenea, a Spanish Ministry of Education and Science project in order to introduce computers in Education. Nowadays, SDSE is being used as a supporting program to teach System Dynamics to school and high school teachers in Atenea project courses run by Comunidad Aut6noma in Murcia.
In this paper, functional characteristics of the system are described, at the same time that SDSE is applied to build and simulate the simple·and classical example of the inventory control system. Nowadays, SDSE is programmed in FBASIC (FUJITSU FM/7 ) and GWBASIC ( IBM PC and compatible)
Session 2: Statistical analysis and econometrics with dynamical systems
Full Feedback Parameter Estimation
Robert L. Eberlein
Abstract: The determination of parameters within a system dynamics model isan important part of the model development and validation process. There are, however, very few useful tools available for working on this. The primary reason for this lack of tools has been the difficulty of applying the theory that has been developed for full feedback estimation. Useful tools can be based upon heuristic application of much of the theory. Rules are outlined that allow the easy determination and application of filtering techniques that deal with the problem of unobservable variables. The attributes of these techniques are discussed in different settings. Application to an example serves to illustrate a number of the issues.
Abstract: In this paper, the dominant approach to the modelling of physical systems is described: it uses local laws and powerful numerical tools. For linear problems, it leads to eigenvalues and eigenvectors, in a suitable functional space, from which it is possible to construct the response to any excitation using the Green’s resolvant. This approach has led to important progress in engineering physics.
Nevertheless, a systemic approach is useful in physics and irreplaceable for living systems. This second way uses global laws of the phenomenon in addition with a dynamical identification of the system using some adequate experiments. We illustrate this method on the modelling of a solar plant, which is correctly represented by a simple ordinary differential equation.
Testing Behavioral Simulation Models by Direct Experiment
John D. Sterman
Abstract: The decision rules in simulation models purport to describe decision-making behavior as it is and not as it should optimally be. Without the criterion of optimality to judge the appropriateness of a decision rule, simulation modelers must rely on empirical confirmation of the structure of their models. In models of small organizations, traditional social science methods may be used. But these methods are infeasible in models of larger systems such as industries or the macroeconomy. This paper shows how direct experiment can be used to confirm or disconfirm the decision rules in simulation models. Direct experiment uses interactive gaming in which human subjects play a role in the system being modeled. The subjects play the game in the same physical and institutional context assumed in the model, and are given the same information set, but are free to make decisions any way they wish. The behavior of the subject can then be directly compared against the behavior produced by the assumed decision rules of the model. An example is described in detail and the correspondence of the experiment to reality is discussed.
Study by System Dynamics of the Problem of the Equalization of the Gain Rate
Abstract: We study the problem of the adequation of the market prices to some “production prices” with which an intersectorial equalization of the gain rate was obtained in an ideal capitalism of free competition. We criticize the treatment of this problem by Marx, Sweezy and Salama-Valier, by its static or aprioristic character. And we propose a system of dynamic regulation utilizing the intersectorial coefficients of an input-output table and supposing full mobility of the capital. The study of this system permits to conclude that the equilibrium values of the gain middle rate and of the production prices depend exclusively of the intersectorial coefficients of the directly or indirectly productive sectors. From this, we study the evolution of the market prices. of the production prices, of the capital organic composition, of the gain sectorial rates and of the gain middle rate from a modification of these coefficients in an equilibrium situation.
The Causal Structure of the Wharton-UAM Model of the Spanish Economy
Emilio Fontela, Antonio Pulido, Ana del Sur
Abstract: The analysis of the causal structure of economic models is a tool for understanding the functioning of existing models, particularly in their interdependent component, and also for assisting the modelors in the process of constructing or modifying large econometric models. In this paper the authors briefly describe the methods of causal analysis and apply them to the Wharton-UAM model of the Spanish Economy. The paper, in English, discusses suggested modifications of the model as a result of the structural analysis and is completed by two Appendices, in Spanish, discussing the theoretical construct of the model and the detailed results of the causal analysis; in an Annex are also reproduced the variables and the equations of the model thus introducing the reader to a fully documented version of the model.
Session 3: Qualitative analysis
Identifying and Displaying Important Feedback Paths
Robert L. Eberlein
Abstract: Fundamental to the practice of system dynamics is the identification of feedback. The theory of linear model analysis and model simplification provide tools for doing this in the setting of linear state space models. The application of these tools in the field of system dynamics has been very limited primarily because the tools are inaccessible and difficult to use. Many of the, difficulties can be overcome by linking the analysis more closely with the original nonlinear model. We do this first by using time plots of model variables to describe behavior and second by deriving a nonlinear feedback model that can be used to exhibit the important feedback structure. The theory for doing this is heuristic, but allows the techniques to be automatically applied with interaction only in the domain of the original nonlinear model and its simulation.
A Dynamic Model of Portfolio Selection: Analysis of Bifurcations
Abstract: In this article we want to predict the dynamic behaviour of a portfolio of assets, i.e., we want to know how quickly it will move towards anew position of equilibrium when an unstable situation has ocurred due to important changes in the risk, (and in some cases in the return) of the securities.
In order to carry out this forecast, first we should locate the points of equilibrium, then analyse their stability and lastly determine where, and under what conditions, the discontinuities appear.
Changes in the return or in the risk of the securities which make up a portfolio can be smooth and this also brings about a smooth change in the portfolio, which is shown in a readjustment in its composition. However, it sometimes happens that, while the expectation of return remains relatively stable, circumstances arise which considerably increase the risk, in which case a serious discontinuity occurrs in the feature of the portfolio.
In this way, we can apply the methodology of Thom’s Theory of Catastrophes in order to obtain valid conclusions using the morphology of the butterfly catastrophe for the portfolio’s feature (efficient, non-efficient and opportunity or pseudo-efficient), employing four control factors: return, variance, transaction costs and risk aversion.
Session 4: Ecological, biological, medical…models
A Dynamic Model for Understanding Eating Disorders
Jack Homer, Richard John, William Cotreau
Abstract: A system dynamics model is presented which integrates current knowledge on the various aspects of normal and abnormal weight control and which provides new insights into the mechanisms underlying certain eating disorders. Anorexia nervosa, in both its purging and non-purging variants, emerges from the model as a behavior pattern tied up with the fear of weight gain which serves to strengthen the individual’s drive toward extreme slimness. Policy tests suggest that appetite-suppressing drugs may be helpful in reducing this fear and its negative physical consequences. The encouragement or discouragement of physical activity may also serve the goal of stabilizing the individual, depending on how different therapeutic objectives are weighted for the specific individual. Future research may take the form of model enhancement or of empirical studies guided by the model’s structure and behavior.
A Simulation Model of Occupational Injury and Illness Causation and Regulation
David F. Andersen, Catherine Crawford, Sue R. Faerman, Erik Mosekilde
Abstract: The United States Occupational Safety and Health Administration (OSHA) regulates the level of occupational safety and health within firms and inspects firms for violations of its regulations. Regression-based evaluations of occupational health and safety conditions in the United States generally conclude that OSHA’s regulation fails to increase either the level of safety or safety-related investment. However, case studies and other forms of qualitative research suggest that regulation does increase both. Resolving this discrepancy requires a research strategy that combines elements of qualitative research and quantitative research. Simulation modelling can be used to bridge these two methods. Generally, the research project constructs a simulation model of accident generation within firms, generates synthetic data from variations of the model, and evaluates the sensitivity of regression methods to variations in the model. This paper presents the structure and base run behavior of the model used in this research project.
Using System Dynamics to Evaluate Policies for Managing New York’s Hard Clam Fishery: Some Unexpected Insights
Marian N. Steinberg
Abstract: A three sector system dynamics model (clams, natural predators, and baymen who harvest the clams) was developed to evaluate measures to counter the sharp decline in New York’s hard clam (Mercenaria mercenaria) fishery. Six management alternatives were evaluated: effect of shellfish hatchery production on increasing the abundance of clams; growing seed clams on racks to protect them from predators; a maximum size limit on the harvesting of clams; limiting entry of baymen into the fishery; a bounty on predators; and setting aside a portion of the bay as a natural nursery. Model results, which were largely unanticipated, are described.
Abstract: For the use of ecosystems with savage fauna it is essential to dispose of -instruments which can let one to simulate the effects that natural circumstances or human actions could have on them.
Because ecosystems are extremely complicated and because we are not able to experiment “in real life” -behavior are irreversible- it becomes necessary- “to experiment in the laboratory” the effects of the different events that may affect its future life.
This “laboratory tests” can be done with the construction of an ecosystem (a model is a formal representation in scale) that later will have to be implanted on a bearing, and will be the object of simulation exercices.
A good procedure of the construction of the model and the simulation is what we calle “System Dynamics” (DS).
The non existence of previous proofs in the use of ecosystem with savage fauna leads conscious of unconsciously to the disappearance of going down of the species in specific ecosystems.
The examples of Kaibab’s land, the “Urogallo cantábrico” or of the grouse -are paradigmatic. The purpose of this work is to introduce concisely the model and the conclusions obtained from its use, for the study of the evolution of the rabbit population in a plot of 10 hectares in South Spain. The rabbit (Oryctolagus cuniculus, L.) has been chosen for its enormous value as a prey for upper birds of prey (Imperial eagle, Royal kite, Black kite, Linx and Fox, etc. etc.)
Computer Model of the Renal Filter Control System
Laura Roa, A. Cantero, A Solis Galera, A.Franco
Abstract: A mathematical model and digital computer simulation of the human renal filtration controls are herein developed. The purpose of the model is to provide a method of analysing renal filtration control hypotheses which cannot easily be tested in an animal or human.
The method used in the construction of the model was system dynamics.
We propose an original formulation for the numerous different variables, eg, Bowman capsule pressure, glomerular absorption, net filtration and other considered variables in the model.
This model can simulate the dynamic functions of variables such as colloidal osmotic pressure, glomerular capillaries, tubular filter, along with other clinical determinants.
The model simulates disparate situations, such as the effects of renal filtration variations of arterial pressure, concentration of plasma proteins…
The results presented coincide with those of other authors.
Dynamic Analysis of the Influence of Reanimation Treatment in Burned Patients
T. Gómez-Cia, Laura Roa Romero, Lazo Zbykowski
Abstract: A non-lineal mathematical model of capillary dynamic has been constructed to study the reanimation stage and the effect that different treatments have on burn patients.
This analysis allows a qualitative and quantitative knowledge of the dynamic behaviour of variables very difficult to quantify in daily practice, like plasma volume, net liquid shift in burned and non-burned areas, etc.
The value and fidelity of the model was obtained by comparison of the reckoned results with those measured in a serie of patients of the Burn Unit of a General Hospital.
Modeling the Common Crane (Grus grus) Population Wintering in Iberia
Juan C. Alonso, Javier A. Alonso, Manuel Quintanilla
Abstract: A field study carried out during the last seven years on a wintering population of Common Cranes (Grus grus) in Spain allowed us to gather accurate field data on-certain relevant demographic parameters: (a) the size of the Western Palearctic population of this species is estimated to be around 40000 birds, and (b) the age composition in autumn is estimated for 1979-85 to be around 13.5% young. These data enabled us to develop and test a population dynamics model which combines the density- and age-dependent effects on productivity and survival rates. The parameters of the productivity and survival functions were varied within biologically reasonable limits. From the series of possible combinations we selected those that fitted our field data on population size and age structure best. Each variable was then varied to study their influence on the model.
Dynamical Interaction between Languages: Castilian and Basque a System Dynamics Model
Abstract: A system dynamics model reflecting the structure of the interaction between the .two languages operating in the Basque Country has been built. People have been classified into three different groups depending on their knowledge of the language. These groups of population are subjected to a normal demographic evolution and to a linguistic interaction. The interaction among the populations is controlled by two major levels: the basque culture and the development factors of the language. The only exogenous input to the model are political actions to raise or to decrease the development factors level. Although the model proves to be sensitive to these actions a delay time of about sixty years is to be expected in the response of the population.
Plenary Session: Instabilities, chaotic behavior and uncertainties in system dynamics models.
Autonomeous Chaotic Behaviour in a Generic Resource Allocation Problem
Abstract: By analyzing the dynamics of resource allocation in a generic management system, this paper illustrates how chaotic behaviour can be internally generated in a typical System Dynamics model.
A company is considered to allocate resources to its production and marketing departments in accordance with shifts in inventory and/or backlog. When order backlogs are small, additional resources are provided to the marketing department in order to recruit new customers. At the same time, resources are removed from the production line to prevent a build-up of excessive inventories. In the face of larger order backlogs, on the other hand, the company redirects resources from sales to production. Delays in adjusting production and sales create the potential for oscillatory behaviour. If allocation of resources is strong enough, this behaviour is destabilized, and the system starts to perform self-sustained oscillations.
To complete the model, we have combined the above simple structure with a feedback which represents a loss of customers when delivery delays become unacceptably long. As costumer’s reaction is increased, the simple one cycle oscillation becomes unstable and, through a cascade of period-doubling bifurcations, the system develops into a chaotic state. We present a relatively detailed analysis of this bifurcation series. Poincaré sections and return maps are constructed, and we discuss how these maps can be used to understand the observed qualitative shifts in system behaviour.
Chaotic Behavior in Predator-Prey-Food System Dynamics Models.
Miguel Toro, Javier Aracil
Abstract: A great interest has been raised recently on chaotic behavior in system dynamics models. This interest is largely justified. The discovery that deterministic systems can show chaotic behavior has deep consequences for the system dynamicist. Among other things, it is well known that strange attractors show a pathological sensitivity to initial conditions. This property impedes the use of a single trayectory (obtained by simulation) as representative of the system behavior. So, the traditional working way of the system dynamicist should be deeply reconsidered if these strange attractors are exhibited by their models. This last is higly possible due to the nonlinear character of these models. Therefore, the system dynamicist should be able to study whether or not those attractors appear in his models. If they appear, then the classical study through the analysis of the trajectory should be rejected, and studies of an stochastic nature -not yet well understood- should be undertaken.
Session 5: Optimisation of System Dynamic models.
A Case Study in Army Combat Modelling
E. F. Wolstenholme, A. S. Al-Alusi
Abstract: This paper demonstrates on approach to army combat modelling using system dynamics. A model is presented of an enemy ground advance which is used to analyse how various adaptive strategies by the attacker and defender during the advance can lead to different outcomes when the combatants meet. Particular attention is paid to the development of performance measures and to the interpretation of results in terms of the underlying feedback structure of the model.
A Case Study in System Dynamics Optimisation
R. Keloharju, E. F. Wolstenholme
Abstract: This paper presents the use of optimisation as a tool for policy analysis and design in system dynamics models and presents a demonstration of its use on the ‘project model’ developed by G. P. Richardson and A. L. Pugh III in their book “Introduction to System Dynamics Modelling with DYNAMO”. The use of optimisation to design parameters, table functions and new model structure is shown to produce every significantly improved performance for this model compared to conventiona1approaches.
Molecule and Generic Structure for Synergy
Abstract: In the evolving terminology within the field of system dynamics, a “molecule” is the smallest combination of structural elements (“particles” and “atoms”) necessary to represent a basic systems concept. A generic structure is the next largest combination of particles, atoms and molecules that conveys the most (or a) general form in which that concept can be identified in and/or represented for real systems. This paper proposes both a molecule and a generic structure for synergy.
Murcia A/I, a Mixed System Dynamics and Linear Programming Model for Regional Investment Planning
Abstract: When distribution of economic goods, equipments, … takes place among different regions, it is expected to carry out in an optimal way, considering “optimal” the way of distribution that assigns more to the neediest regions; thus, numerous factors such as economic conditions, actual equipments, social conditions, population, etc, should be taken into account.
The presented model has a double aim: firstly to show the present behaviour of distribution system of investment in Comunidad Autonoma de Murcia, regionally, and secondly to get this distribution to optimize a linear function that represents the regional social welfare as a consequence of the social welfare in each region of the Community and dependent on linear constraints.
To reach these objectives, a mixed model that combines both System Dynamics and Linear Programming techniques is constructed; a relation between both procedures is established in order to simulate both the natural behaviour of the distribution system and those decisions that make this distribution to be optimal.
Along this report the method carried out to handle mixed models as well as the particular model MURCIA A/I are described.
Session 6: Status and future of System Dynamics in the World, in the U.S., in Europe.
A Study of System Dynamics from the View of System Theory
Qifan Wang, Yang Xinnong
Abstract: Since L.V. Bertalanffy first brought forward the general system theory, people have been paying more attention to research work from the systems point of view, thus bringing about the development of some system scientific fields such as systems engineering, operations research and management science, etc.
Now, in addition to general system theory, there are many new subjects related to studying system ‘dynamic behaviors and self-organization such as synergetics, dissipation structure theory, etc.
In this article, we study system dynamics from a philosophic viewpoint and try to study important points and methods that can be introduced by systems theory. We search into the relationships between system dynamics and other fields.
Is Systems Dynamics Rate of Diffusion Slow?
Andres Esteban Breiter
Abstract: This paper examines the causes and effects that interact to determine the rate the causes and effects that of Systems Dynamics diffusion.
The use of Systems Dynamics implies both a way of conceptualizing the models of existing systems and the use of such models to gain a better understanding of the systems’ behaviour.
Given the high potential of Systems Dynamics to aid in understanding a very wide variety of systems in many areas of human endeavour the Systems Dynamics practitioners worry regularly about its slow propagation and frequently express anxiety about the future of the field. They tend to forget, however, that the potential usefulness of their approach is obvious to them but is hard to appreciate by the would be users and eventual beneficiaries of the improved solutions derived from applications of their expertise.
This paper focuses on the causes and effects that in the authors’ opinion interact in the diffusion of Systems Dynamics and suggests actions that may eventually help to accelerate the process of its broad adoption.
On Extending the Institutionalist Paradigm: The Appropriate Place for System Dynamics within the Economics Profession
Michael J. Radzicki
Abstract: After enduring years of criticism from prominent economists, many members of the system dynamics community have concluded that economists do not like system dynamics. This article argues that this conclusion is not entirely correct. The economics profession can be divided into two methodologically different camps: the mainstream or neoclassical economists and the institutional economists. Although neoclassical economists do not see system dynamics models as being scientific because they do not adhere to the tenents of logical empiricism, institutional economists construct models in a manner that is strikingly similar to the system dynamics method. Indeed, it is shown that system dynamics can be used to strengthen and extend the institutionalist paradigm in economics and thus has the potential to find a permanent home within the profession.
The computer people took seriously the evidence that people are not maximizing-rational and decided to find out by empirical study how decisions are actually made. Thus they became, in a way, heirs of the institutionalist program ….Philosopher of Science Paul Diesing
Studying the Relationship among the Whole, Parts and Environment of a System Dynamic Model
Qifan Wang, Guangle Yan
Abstract: From the viewpoint of system dynamics the whole structure and functions of a system do not simply equal the algebraic sum of the parts which the system consists of. There universally exist mutual relationships between the transmition and exchange of information, energy and material within the whole system, its parts and its environment. The aim of this paper is to study the organic ties among the three of the whole, parts and environment of a system and the transmition involved under specific conditions. In this paper, the logical relationships between the internal and external parts of the system are described. Two concepts of the transmition matrix and the relationship matrix are presented along with the definitions of the grades of the grades of variables. Their concepts and definitions, combining the theory of the model reference self-compensation, are used to form a new method by which the functions of the structures and relationship between the whole system and its parts can be identified. Some satisfied results have been obtained from testing this new method on the Boom-town Dynamic Model.
System Dynamics in a G.S.T. Framework
Rafael Rodriguez Delgado
Abstract: Systems Theory has developed without inner coordination.
The General Theory has been general in the sense of trying to reach a global viewpoint from the perspectives of science and philosophy. But it has not perceived its structure as a whole. It has grown in complexity without integrating its parts.
Systems Dynamics has expanded in relative isolation. It has developed into a closed methodology with fixed principles and structure. To a great extent it has been equated to the Forrester’s methodology applied to industrial, urban and global systems.
It would be valuable to place the Dynamic approach in a wider context. It is assumed here that in a General Systems methodological framework the same system can be considered from three different, but complementary, viewpoints: Static, Dynamic and Dialectic. It is also assumed that closeness and openess of systems are relative states and that analysis and synthesis should have analogous methodological weight.
Systems Dynamics appears as a central node in a systemic methodology that should integrate different approaches and viewpoints into a coherent whole.
Session 7: Economic applications
The Time Delay and Oscillation of Economic System
Fan Chong-Hui, Zhang Yi-Min
Abstract: The time delay θand capital life-time βof economic system must be considered in discussing the system’s dynamic behaviour. In this paper a model of economic system with time lag has been proposed to deal with time delay and life-time. The core of this model is investment decision equation, in which the transfer function has been introduced. By selecting appropriate coefficients ai and bj the desired dynamic behaviour can be obtained. The impulse response h( t)of the system is defined by using numerical solution of its characteristic equation. The numerical solutions for proportional and proportional-plus-integral control system with 60 different sets of θ &βhas been calculated. According to the calculating results we use multiple regression analysis to get the regression equation between the critical oscillation parameters (period, amplification coefficient and amplitude) and time delay & life-time. It is convenient to apply these regression equations for choosing parameters.
Limits to National Development:& Resources or Resource Allocation Processes?
Abstract: This paper re-examines the economic development problem and establishes that organizational arrangements underlying resource use at the social, political, and ecological levels, not shortage of resources per se, or their inefficient employment, are responsible for creating conditions of underdevelopment and for the failure of the well-intentioned economic development efforts made in the past. Three levels of national organization are examined: the social level which is concerned with the production and distribution of income among various cross-sections of society; the political level where decisions are made to allocate resources to public welfare or to maintaining control over the public; and the ecological level where a resource mix is selected for use on the basis economic and technological considerations. The analysis is based on three separate formal system dynamics models of the resource allocation processes dealing with each of the three levels of national organization discussed above. Appropriate institutional arrangements for fostering sustained national growth are explored.
Modeling Fuel Pricing Policy and Consumption Patterns
M.T. Tabucanon, K. Saeed, Q. Suhail
Abstract: This paper examines the domestic energy consumption in Pakistan in the backdrop of the government’s pricing policies using a system dynamics model as an explanatory tool. In the context of policy analysis, the simulated behavior of the system are tested based on various pricing schemes of the competing fuels. The simulation experiments reveal, among others, that Pakistan’s energy system structure is such that any policy involving government control over the prices will eventually result in an increase in burden on family income of rural and urban poor classes mainly and urban middle class partially. It seems that the only way to redistribute the burden on family income, minimize the burden on national economy, and also achieve conservation of fuels, is by allowing the price of fuels to be determined by the supply-demand conditions of the market.
Interfuel Substitution in Oecd-European Electricity Production
Abstract: A dynamic simulation model of interfuel substitution in Oecd-European electricity production is presented. A combination of a priori information and a calibration of the model to hictorical development produces several important results. Adjustment times are much longer than usually assumed, and price elasticities are much higher. Both the simulation model and econometric estimates indicate that the LOGIT model is a better representation of fuel choice in the sector than a constant elasticity function. The LOGIT model explains why estimates of price elasticities tend to vary over time. It also indicates that a fuel can price itself completely out of the market. Finally, the results indicate that coal is protected equivalent to a price subsidy of about 36 percent.
An Investment and Pricing Problem: A System Dynamics Approach to the Differential Games
Hannu Kivijärvi, Margareta Soismaa
Abstract: This paper deals with the analysis of the classical investment and pricing problem of a monopoly faced with competition from substitute industries or marginal firms in the same field. The monopoly owns a finite level of a resource (ie, the stock of an exhaustible. resource), whose usage is to be divided optimally over a finite planning horizon. The demand for the resource is described by a downward sloping demand curve which is affected by the measures of the competitor. The monopoly and its competitor are maximizing the present values of their net profits over the planning horizon. The problem is first formulated as a non-cooperative differential game. The necessary conditions for the Nash solution are derived.
The necessary conditions for the solutions are stated as a two-point boundary value problem which admits also an analytical solution if some simplifying assumptions are made. However, to relax these assumptions numerical solutions are computed by employing System Dynamics.
In terms of System Dynamics the two-point boundary value problems have initial states for some level variables and terminal states for some other level variables. To solve this problem with System Dynamics we have used the Newton-Raphson method. In the Newton-Raphson method two System Dynamics models are needed: one to produce a Jacobian matrix and another to produce solutions for the original problem.
Economic Growth and Development Policy in Oil Dependent Indonesia
M. Tasrif Arif , Khalid Saeed
Abstract: This study uses a system dynamics model to understand the process of economic growth in the oil dependent economy of Indonesia. Many long-run growth patterns resulting from the various intuitively appealing development policies are analysed and an attempt is made to identify the best policy set for attaining a sustainable growth pattern. The study shows that influencing factor prices in a way to facilitate adoption of capital intensive technologies increases acceleration of growth and is a key policy to sustain growth in the long run.
Feedback and Delay in Planned Economy System
Chogjie Zhao, Chingrui Xu
Abstract: Slow feedback and passive control are the major problems in pure planned economy country. In this paper we compare two kinds of economy control forms which exist now: planned control and market control, prove why our country take economy reform as the main work in the Seventh 5-Year Plan and show what function these reforms will have. The method is based on system dynamics. Simulation tell us: the difference between planned economy and market economy consists in their feedback control form, if we can combine the advantage in market control with our system, our economy system will be improved greatly.
Planning Conservation Programs Decision Support with the Conservation Policy Analysis Model
Patrick Barton, Mike Bull
Abstract: System Dynamics has proven to be a useful paradigm for the construction of a policy analysis model in support of energy conservation decisions in the United States Pacific Northwest. This paper outlines the most important complexities faced by the Bonneville Power Administration planners, how system dynamics has provided a framework for analysis and how the integrated model currently used by staff members (the Conservation Policy Analysis Model) has been applied successfully to a wide range of problems.
System Dynamics and Circulatory Analysis: Proposals for an Alliance
Moisés Garcia Garcia, Francisco Serrano Moracho
Abstract: Our purpose is to set up a dialogue, a scientific exchange, between CIRCULATORY ANALYSIS and SYSTEMS DYNAMICS, since we belive the two -disciplines to be complementary. In fact, we would go so far as to say that S.D. represents the natural development of C.A.
We consider there are well-founded reasons to expect the cooperation between the two disciplines to be profitable in helping to subdue the system of economic circulation and to subject it to a rational control.
Circulatory Analysis can offer Systems Dynamics the conceptual riguorousness of a theory of circulatory systems developed from solid bases, and even some new concepts which may be very useful (for instance, those of Circulatory Process and Complex Circulation). On the other hand, Systems Dynamics can offer all its engineering capacity to produce working models.
In order to show more clearly what Circulatory Analysis is, we have made a small toy, a model constructed to simulate the behavior of the system of economic circulation in a commercial business. It is extremely simple (it is, after all, a toy), but the same methodology used for its design and construction can make it possible to produce machines, that is, simulator models, to any degree of complexity.
Studying Dynamic Effects of Industrial Capital Retrofit and Energy Price Adjustment on Energy Development in China
Qifan Wang, Xiaobo Zhang
Abstract: This paper tries to use System Dynamics as a tool to analyze some existing problems in China’s energy system. The paper first points out some most severe energy problems in China and the policies that people suggest toward the solving of these problems, then reveals the dynamics of these policies through simulations on an Energy Dynamic Model that we built. The analyses cover the issues of energy production and supply system, energy price, energy shortage, and industrial capital retrofit toward energy conservation, etc.. Some conclusions are derived from the analyses which are valuable for the solving of China’s energy problems. And System Dynamics is believed to be an effective approach in energy price analysis in China.
Session 8: Industrial and Corporate Developments
Employment Policy and Expectations
M. D. Soto Torres, R. Fernández Lechón
Abstract: The paper studies with the help of a model the employment decisions of a firm through a business cycle which maximizes its discounted income and assumes that the forecasts are perfectly corred.
The firm produces a output function of number of workers employed by the firm at time t. The firm’s labor force increases over time as a result of layoffs and quits. The firm can recalls workers at time t only if it has an inventory of previonsly laid off workers. The firm’s output is supposed superior or equal to demand (function of price and time) at any time. The solution to the maximization problem will then yield an optimal output and employment plan which the firm proceeds to implement until its expectations about demand at time t.
A Policy Analysis Model and the Development of the Finnish Forest Sector
Abstract: The study aims to assess the potential of the forest sector to maintain its leading role in the Finnish economy. The long range future alternatives are simulated by means of a System Dynamics model called MESSU. It is shown that within the limits set by the availability of wood and the low profitability of the forest industry, the growth of total production in the forest industries cannot meet the projected increase in international demand with the present product mix.
MESSU covers the whole forest sector (forestry and the forest industry), which makes it possible to study the interaction between the different parts of the sector. The model is built up of seven submodels (modules): forest, forest ownership, roundwood market, harvesting, forest industry, end product market and capital market.
MESSU does not only consider economic features of the forest sector, even though they are a central part of the model. Biological (timber growth) and technical (e.g. efficiency of forest industry production and harvesting) features are also included. Further, sosio-economic issues, such as population, urbanization and labor supply dynamics, are considered.
Study of Demand Behavior: A Modular Approach
Abstract: Business decisions about investments have to be guided by the careful study of market behavior. In this paper an attempt has been made to study the market behavior adopting a modular approach. The total demand of a product in a market gets influenced by a set of four major feed backs related by market saturation, capacity expansion, price fluctuations and motivational efforts. In the paper each of the feed back has been seperately discussed to arrive at a feed back structure which can be used for designing the policies related to expansion of capacity, pricing, motivational efforts etc.
Evaluation of the Benefits from Using System Dynamics on Personal Computers for Corporate Financial Management
Albert Herremans, Philippe Wilmes
Abstract: DYNAMO has been used for many years on mainframe computers. Like many other applications programs and computer languages, it has been made available on Personal Computers. Will that make System Dynamics easily available to many potential users who never tried to use it on mainframes? Does one need to be an Information System specialist to use DYNMO on a PC?
These are the questions to which this paper intents to give an answer to. Subsequently, we used DYNAMO on a PC for a very simple financial application, and compared it superficially with the (already) traditional approach of spreadsheets.
Does Stock Control Need Modelling or Simply Experience? System Dynamics of Hospital Linen
J.P.Oostveen, D.J. Sweeny, A. de Weyer, E.v.d. Leest
Abstract: The St. Radboud Hospital of the University of Nijmegen, The Netherlands is sponsoring a System Dynamics computer simulation designed to study the hospital’s textile (bed, catering, medical linen and uniforms etc.) circulation process.
Competitors’ Reactions to Introduction of a New Product, A Selling Case
U. La Roche
Abstract: For a utility application in the capital goods sector use of new technology in production gave the possibility to have a new product at much lower cost than competition
There were about five competitors with approximately equal market shares. In order to optimize timing of marketing and production an analysis of market and competitors’ reactions was started.
The work reported covers the main steps and findings of this analysis made in preparation of execution of the optimized marketing exploit.
These steps cover conceptualizing of market-competitor relationship, modelling and simulation to define sensitive parameters, defining some robust market policies and analysing the operational information requirements in executing a set marketing concept.
Specific results obtained were above all elimination of some crude “feel of the pants” notions how to sell and confirmation of the importance of a selling policy even in a seemingly orderly and settled market environment.
Other results contributed very much to an understanding, why a new product at much lower cost is only in part able to gain market share in a setting of wary competitors.
Decision Support for Marketing New Products
Peter M. Milling
Abstract: The control of new product growth and market penetration is a key task for corporate management. The concept of Decision Support Systems is applied to this field of problem solving. A general model of innovation diffusion is presented and used to study market response and profit impact of different strategies. Its analysis suggests a marketing approach which aims at rapidly gaining sales volume. Attractive prices and fast capacity built-up take effectively into account the dynamic environment.
Know-how Transfer by Multinational Corporations to Developing Countries – A System Dynamics Model with Spiral Loops
Peter P. Merten
Abstract: The course of know-how transfer of multinational corporations in developing countries is presently considered to be very problematic from the view of multinational corporations as well as from the view of developing countries. This paper first develops a descriptive model of this problem. The descriptive model is based on empirical and secondary statistical investigations of Japanese, US-American and German assembling industry multinationa1 corporations (automotive industry, electrical industry and mechanical engineering industry). The descriptive model shows that the know-how transfer process is a process of structural change resulting from the interaction of multinational corporations, local corporations and developing countries. Based on this descriptive model we have developed a formal mathematical model of the evolutionary process of know-how transfer by introducing “spiral loops” as a methodological extension of the system dynamics approach. The spiral loop concept which is based on new developments in evolutionary theory and in the field of artificial intelligence is used to model the qualitative changes in interaction processes which are responsible for structural change and evolution. The feedback loop concept and the concept of shifting loop dominance are used to model quantitative changes in interaction processes. The combination of the traditional feedback loop concept of system dynamics with the spiral loop heuristic allows us to model dynamic interactive processes between two or more autonomous systems in their quantitative and qualitative dimensions. Plots from simulation runs of the model show the evolutionary pattern of the existing know-how transfer process, which is considered problematic. We have analyzed different patterns of this process with model tests in order to generate policy and strategy recommendations for managers of multinational corporations and politicians in developing. countries.
A System-Behavioral Methodology for Business Policy Research
Roger I. Hall
Abstract: A process modeling approach is used to describe three major elements of policy making, namely, the workings of the corporate ,system of a firm, its representation in Managers’ Cause Maps, and the Policy Formation Procedures used by the policy making elite. System Dynamics provides an expert system to aid the construction of the Corporate System. Cause Map and Behavioral Decision Making theory, on the other hand, provides the artificial intelligence (modeling the collective decision making behavior of a senior management) that drives the Corporate System. Potential applications of the methodology are put forward.
A Multi-Sector Model of Inventory-Production Fluctuations: The Impact of Local Information on Global Performance
Ernst W. Diehl
Abstract: Inventories of finished goods are added to the static input-output model. This addition allows one to relax the assumption that production can instantaneously track incoming orders. The reformulated input-output model exhibits production-inventory cycles over a wide range of parameter constellations. The model can be used for an extensive dynamic analysis of short-term production-inventory fluctuations in different sectors of the economy. In particular, it can be utilized to understand the extent to which each sector’s fluctuations are synchronized and dependent on the fluctuations in the other sectors.
The cause for the potentially oscillatory behavior of the model is analyzed. It is shown that the main reason for the oscillations lies in the assumption that the actors in the model do not know why orders are issued. They cannot distinguish whether incoming orders are issued because the recipients want to adjust their inventories or whether they are issued because the recipients have changed their long-term production plans. This result points out that one dimension of a successful stabilization policy might be an improved information policy. It is suggested that an extension of the model could be used to explain the production-inventory fluctuations during business cycles and to achieve a more detailed understanding of the behavior of different sectors during such cycles.
The Role of the Women in Business Management
Jose María Bueno, José A. D. Machuca
Abstract: The main purpose of this work is to study the role of the women in different levels of business management. The system under study is composed of: a)business sector, in which women carry out their activities, b) educational subsystem, which provides them with the necessary skills to ascend to different managerial positions, c) cultural and socioeconomic conditions of the country, which influence : the motivation of women for this kind of work, the entrepreneurial attitude to hiring females in firms.
The characteristics of the system together with the pursued objective bring us to the choice of System Dynamics as the most adequate method for our study. Using as our starting point a causal diagram of the global system, we have divided it in sectors. These represent the different aspects above mentioned.
This is a long-term project from which we hope to obtain partial results to be presented in the 1986 System Dynamics Conference.
A Strategic Study on the Development of Electronic Industry in China
Qifan Wang, Dong Jianglin
Abstract: With the rapid development and wide application of microelectronics, the electronic industry is playing an ever more important role in modern economies. Backed by the socioeconomic circumstances, a system dynamics model (SDEIC) is constructed to investigate the development of electronic industry andto give a description on the future of microelectronics in China in some way. The analyses and simulation results show that there will be a prosperous period for the development of the electronic industry in the coming twenty years with a vigorous investing requirement and at a relative high growth rate. A notable characteristic is that the development is unbalanced with electronic consumption products dominating the market in terms of volume in the period concerned.
Prospective Study of the Footwear Sector.
Bernardino Cabrer Borras, Amparo Sancho Perez
Abstract: The principal objetive of this study is to determine the production trend until 1995, taking into account the future behaviour of the variables which are involved in the explanation of the home market demand as well as exports of footwear.
The forecasts have been made using a prospective model. By prospective is meant the effort involved to imagine the different futures which may be caused by the behaviour of the “actors” within the logial limits of the systems through which they act. In this paper a distinction is made between the variables whose dynamics are almost always constant and those which may be affected by the decision of the ‘actors’ or by unforesceable events. The prospective study seeks to understand the plans which the actos will try to carry out and will affect its future behaviours.
These options become especially clear in the construction of partial or complete scenario. Scenario, according to the definition of Fontela (1980) is the script of a theatrical work about the future in which economic and social agents would be involved. To construct a scenario for the future is a creative task in which, implicitly or explicitly, all long-term decision makers play a part.
Hence to study a scenario of the development in the next decade is to analyse one of the potential futures, being fully aware of the essentia1 unpredictabi1ity of the future and of our full freedom of choise.
A System Dynamics Perspective on JIT-Kanban
Abstract: Just-In-Time (JIT) production is the notion of producing the necessary products in the necessary quantities in the necessary time in every process of a factory and also among companies. It is not uncommon to find JIT used synonymously with “Kanban,” which is the name for a specific inventory replenishment system developed by Toyota to accomplish JIT production. The Kanban system employs cards (kanbans) to signal both the need to deliver more parts and the need to produce more parts. A unique feature that distinguishes the kanban-based JIT system is its unique “pull” nature.
The paper begins with a review of JIT production and the Kanban system. Then, using the structuring principles of System Dynamics, a simulation model of a kanban-based JIT production system is developed. The formulation effort begins with the “simple structure” of one production stage. By connecting a few of these “basic structures” and adding a market interface module, a complete multi-stage manufacturing system is developed later.
To test the internal consistency of the model, several simulation experiments are conducted. The unifying theme in these experiments is the issue of flexibility: How well does the system adapt to changes. The simulations are thus designed to show, for different management policies, the behavior of the system in response to unexpected circumstances. The following cases are considered: normal response, changing the number of kanbans, a breakdown, small and large demand increases, bottlenecks, and capacity planning. Finally, the results of these simulations are used to point out some of the managerial trade-offs involved in JIT production.
Although the major contribution is the conceptualization and formulation of the system dynamics model, the paper lays the groundwork for subsequent normative research in the field of operations management.
Session 9: Expert Systems and System Dynamics
A New Approach to Environmental Impact Assessment
Paula Antunes, António Camara
Abstract: A new approach to Environmental Impact Assessment (EIA), based on system dynamics concepts is presented in this paper. System dynamics models will however be useful in EIA only if people are able to develop”good” models. The conceptual basis for building an expert system designed to guide people in developing system dynamics models is introduced in this work. Such an expert system will have two main modules: a system dynamics component, which will include basic system dynamics concepts and heuristics; and a specific application component, which will consist of the main relations and rules governing a givenenvironmental area. The system will also include an interface with a dynamic simulation language and with a decision aiding formulation.
EASDM: An Expert Aid for System Dynamics Modelling
Jose Carlos González Cristobal, Gregorio Fernández
Abstract: In this paper an Expert Aid for System Dynamics Modelling (EASDM) is introduced, a user friendly, interactive software tool which helps users unfamiliar with System Dynamics and computers, to construct their models from the formulation to the simulation. The most important feature that distinguishes this aid from its closest predecessor (ASDM) is the incorporation of an expert system capable of carrying out the conversion from the causal diagram to the Forrester schematics in a semiautomatic way. This is possible because, within the context of the causal diagram, there is an implicit set of “rules” which allows the classification of quantities. EASDM has been programmed in PROLOG and Pascal for personal computers with the MS-DOS operating system.
LSC: A Portable Continuous Simulation Software
M.Gaci, A Babaamer
Abstract: This paper presents a Continuous Simulation Software (LSC) developped in our laboratory.
The first version of this software treats dynamical systems , that are described by a set of explicit linear or non linear algebro-differential equations .
The software has an interface (High Level Language), that permits an auto-guided dialogue with the user.
The internal architecture of the system is structured in two subsystems: a control subsystem and an operating subsystem The package contains a library of algorithms and external functions that permits simulation models from different fields (socio-economic, technological … )
A Behavior Analysis Expert System for System Dynamics Models
Abstract: There are many ways to combine Expert Systems and System Dynamics. In a short overview the paper will show useful basic combinations. As an experimental project BAMBOO will be introduced. It is primarily designed to test the usefulness of descriptive knowledge processing techniques for building and using System Dynamics Models. BAMBOO holds expertise of all SD-objects and structures, their possible combinations and the behavior they cause. BAMBOO generates the necessary knowledge about the user model by a system driven dialog. On the basis of this knowledge it shows the conclusions the model implies. For instance, BAMBOO determines which variables are sensitive and how the model will propably respond during the simulation.
MAPS: an Expert Advisor for the Qualitative Analysis of Dynamical Systems
M. Andretta , M. Lugaresi, P. Mazzanti, R. Serra
Abstract: The analysis of the evolution of non linear dynamical systems is a complex task. The cases where: i) the model equations can be regarded as a careful and reliable representation of the real system and, therefore, need no revision or modification; ii) the parameter values are precisely known; iii) the initial conditions are precisely known, are rather rare.
At least one of the previous conditions is not fulfilled in most of the systems of interest for System Dynamicists. Therefore qualitative analysis of dynamical systems, i.e. the study and classification of their asymptotic behaviours, is of extreme importance, at least in long term models.
The methodologies of knowledge representation recently developed in the field of expert systems can be applied to this problem. We therefore developed MAPS, an expert advisor for the qualitative analysis of dynamical systems. MAPS takes the system equations as input, classifies them according to their features and performs the necessary calculations at each stage, sending appropriate messages to the modelist.
At present MAPS deals with autonomous second order systems of ordinary differential equations. Further developments are foreseen concerning the study of higher order sytems and the design of an “equations database” for comparison with previously analyzed equations.
Focusing on the Growth Rate of Technological Adoption
Frederick P. Wheeler
Abstract: Models of substitution and adoption of consumer durable technologies typically focus on the level of adoption or the level of cumulative sales of the product. Although these variables may be of interest, decisions on market entry and the judgement of future return on investment are linked to the rate of change in adoption level. The percentage change in the current level of adoption, the growth rate, is more relevant, more meaningful and more sensitive a measure of past and future trends than is the level itself. This is an appeal for system modellers and forecasters to focus their attention on growth in studies of technological diffusion.
Linguistic Dynamic Modelling Using Logic Programming
A. Câmara, P. Antunes, M. Pinheiro and J. Seixas
Abstract: A new dynamic modelling methodology, SLlN, allowing for the analysis of systems defined in qualitative or quantitative terms is presented. Simulation of qualitative characteristics is performed by applying a set of logical rules which include base, tactical, strategic and structural change rules. Quantitative simulation applies traditional system dynamics concepts. To make the transition from qualitative into quantitative modes, logical rules are also used. SLIN is advantageously implemented on a very high level language such as PROLOG, as shown in this paper. To illustrate its potential applications, simple water quality models are included.
Session 10: Public and Social Applications
A Simulation Model of the Tokyo Metropolitan Region
Toshiro Shimada, I.Tokunaga, A.Otaki and T.Okubo
Abstract: The population of the Tokyo Metropolitan Region increased by about 3 millions in the five years between 1965 and 1970. This increase was due mainly to the flow of populations from the outer field of the Tokyo Metropolitan Region. Until around 1955, population increases were noticeable within the special wards of the metropolis. However, while there has been a recent lull in the increase rate of in-migration, there has been a remarkable increase in the amount of out-migration from the special wards to the four adjoining districts, the Tama district, Chiba Prefecture, Saitama Prefecture, and Kanagawa Prefecture. Out-migration exceeded in-migration in 1967 for the first time since the end of the War and the gap has been increasing year by year. On the other hand there has been gradual rise due to natural increase (the difference between births and deaths) in recent years, which has come to occupy a greater part of the population increase within the area of the Tokyo Metropolitan Region.
Our model therefore was formulated to represent such relations between the ward area and the four adjoining districts, as migration, residential effect and commutation.
We have divided the whole system into 5 sectors, corresponding to the ward area, the Tama district, Chiba Prefecture, Saitama Prefecture and Kanagawa Prefecture. Each sector is subdivided into population, residence, and enterprise sub-sectors.
The simulation was run for the 150 years from 1900 to 2050 and the results contained World War II effect on the population, the number of residences and enterprises of the ward area.
CRISYS: A Model of the Criminal Justice System in the Netherlands
R. O. Beijdorff
Abstract: System Dynamics Research and Consult has been asked bythe Ministry of Justice in The Netherlands to develop a simulation model of the criminal justice system. In this system a number of feedback mechanism are present that have negative side effects on the society. The first steps in the development of the model were taken. A number of small models of parts of the system were made to gain insight in the behaviour of some variables that are hard to quantify. A larger semi-dynamic model was developed to study the behaviour of the variables that are better to quantify. All models have to be integrated in the next part of the project in order to refine the forecasts.
Modeling School Finance Policy Using Simulation to Test A Priori Assumptions
George P. Richardson, David F. Andersen, Robert E. Lamitie
Abstract: In many of the United States, attempts to reform the funding of public education to reduce disparities among school districts have been disappointing. For this study of state aid-to-education in Connecticut, a system dynamics model of local district budgeting behavior was formulated, replicated seven times to represent all the school districts in Connecticut divided into seven clusters, and linked to a state-aid sector that dispenses aid according to the state’s current guaranteed wealth formula. Simulations of a single cluster and the seven-cluster model suggest that the guaranteed wealth formula will not, by itself, narrow the gap in per-pupil expenditures in rich and poor districts, as intended.
The study described is a relatively pure case of policy modeling designed not to confirm hypotheses but rather to draw inferences from puzzling sets of assumptions about state and local behavior. Reflecting on this case, we suggest six conditions that appear to indicate that a policy problem is ripe for the sort of contingent, inference-generating analysis illuminated by the Connecticut study. Some speculative methodological connections to cognitive science are also suggested.”
Industrial Site Planning as a Tool to Control Regional Employment – A DYNAMO Model –
H.H.E.W. Eijdems, D.J. Sweeny, B.J. Brouwer, W.R. Snel, J .M. den Breeje
Abstract: Holland is a little, crowded country with (like most nations in Europe) a high degree of unemployment. On the one hand the government tries to provide an adequate amount of industrial sites in attempting not to obstruct economic growth. On the other hand this puts a high claim on the amount of scenery still extant in our country. Therefore the council of the central province in Holland asked for an investigation about the relationship between the supply of industrial sites and the influence on the increase of employment in each part of the province. As there are six employment-office area’s in this province, a partition was made in six regions. Several branches of employment have quite different effects on claims for industrial sites, so there was also a division made in three economic branches. This results in eight teen equations for many of the relationships in the same form, but with different parameters. Therefore the DYNAMO – III -language was used in model-building to take advantage of the array possibility. The final result is a computer-model comprising about fifty array-equations, which allows the calculation of the area of industrial sites in different stages of development in each region and gives the spreading of employment over the province until 1995.
A System Dynamics Model of Sexual Harassment
James M. Norris
Abstract: The majority of women report that they have been victims of sexual harassment (Safran, 1976, Tangri, Burt & Johnson, 1982). Sexual harassment has been linked, both theoretically and empirically, to psychological and physiological stress, often accompanied by somatic symptoms such as headaches, nausea, and loss of concentration, as well as decreases in job performance and increased absenteeism and turnover. In addition, estimated losses in the federal government alone were in excess of $189 million over a two year period. This paper is one of the first to unify the past research and empirically consider sexual harassment in terms of its underlying mechanisms. It is also one of the first to examine the dynamics of the harasser and the organization in which the harassment occurred. Interactions between the victim, harasser, and organization sector are explored. Results indicate that longstanding organizational traditions of sexual harassment may make it difficult to eliminate harassment in the near future without a comprehensive group of policies concerned with eradicating sexual harassment.
Prospectives for Growth: A System Dynamics Study of the Roman Catholic Priest Population of the Netherlands
J.P. Oostveen, D.J. Sweeny
Abstract: Sponsored by a Dutch Roman Catholic Foundation a System Dynamics computer simulation model has been developed to study the population dynamics of priests of the Dutch Roman Catholic Church.
Few vocations since the second half of the sixties led to a disproportional ‘going grey’ of the priest population. This is manifested not only in the unbalanced age structure but also in a relatively high number of retirements.
The model (see enclosed flow diagram) structures on the one hand the physical demographic processes and on the other embodies a theory based on observation of qualitative aspects of disaggregated priest, believer and non-believer populations. Church attendence figures for instance are used as a measure of vocation potential.
The model is used to articulate the insights on the influence of policy alternatives on priest population in the coming 50 years or so.
Development of a Policy-Supporting Simulation Model of the Records Management System of the Dutch Public Authorities
Abstract: The Dutch public authorities are confronted with large backlogs in processing the archives of their services. In view of this, the Ministry of the Interior, which is responsible for coordination of these processing activities, wanted to have a planning model for simulation, in a quantitative sense, of the archives movements within the public administration. The underlying thought was that such a model would enable problems in the fields of depot space, cost structure, allocation expertise and processing speed to be approached in a more adequate manner. A first exploration of the problem area (October 1984 – April 1985) showed that the quantitative problem of the processing backlogs is to a great extent affected by qualitative processes within the records management system and between said system and the client system. It was concluded that a planning model focused on quantitative factors cannot make an effective contribution towards solving the problems as the effects of measures aimed solely at efficiency will in the long run be affected adversely by qualitative processes. When the study was continued (September 1985 – April 1986), it was therefore decided to further investigate the processes of a more qualitative nature and to analyse their coherence. The results obtained provide a first step towards development of a simulation model for the records management system which, while supporting the relevant policies in this field, forms a tool for determining the, effects of policy changes in the system both in the short and in the long run.
Development of a Common Communication and Control System for System Dynamics Type of Simulation Models
H. Krallmann, B. Rieger
Abstract: Today for managers or in general for non data processing experts the use and application of simulation models is of very high expenditure.
Editing and changing model parameters, studying the simulation language or applying e.g. a graphical standard software package are very unusual activities for this special user group. Due to this situation it cannot be expected that simulation models which deliver very important results for decision support get near to these people.
In this paper a user friendly communication and control system is presented, which offers an optimal user guidance in modifying and running simulation models, in creating a user friendly graphical output and in the interpretation of the model results.
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