This paper deals with the structure of the system of arms transfers by the United States to the rest of the world. Arms transfers play a significant role in the political, economic, and military affairs of most countries. Because of the diversity of opinion about the necessity for transfers and their true effect, a single policy concerning arms movement has been impossible to devise. This research is the first step in providing a model that can be used to study the effects of transfers and to evaluate policy concerning arms movement.
In large numbers of U.S. urban elementary schools, there is a multiplier effect which operates to reinforce high achievement for initially high-achievers, average achievement for initially average-achievers, and failure for initially low-achievers. This problem is aggravated by the fact that initial levels and perceptions of achievement are systematically related to social class. In part, poor children enter school with less readiness for reading. Evidence also suggests that, actual achievement aside, teachers tend to perceive lower class children as low-achievers simply because they exhibit lower-class family, dress, and behavioral characteristics. In contrast, there are a relatively small number of “lighthouse” schools spread through out the country in which students, often minority and/or poor, achieve far better than home or SES variables would predict.
Any firm or industry which experiences marked cyclical fluctuations in both output and demand can provide a testimony of the damaging effects such oscillations have on profitability. Perhaps none more so than the British Steel Corporation (B.S.C.) whose record in this respect is rather poor. For such industries, therefore, any methods which management science can provide as a means of analysis of the causes and effects of such cycles are to be welcomed. It is suggested in this paper that system dynamics provides an important framework for analyzing the causes of cyclical behaviour in economic systems and that it is this area of application which possesses the greatest chance for successful demonstrations of its use. It is probably for this reason that work using the methods of system dynamics has concentrated, in Gt Britain, on economic systems.
At the beginning of the seventies, grave concern existed over low mobility of researchers due to the stagnation in growth in the research capacity available. Through a strong expansion in research capacity prior to this condition of stagnation, the age of researchers was relatively low. It was feared that the small natural turnover (as a result of a low average age) together with the low mobility would lead to a collective aging of the research corps itself. This aging factor was considered to be a threat to research as a whole since it could lead to mental fixation and loss of creativity. In addition to this, the expectations for making a career and the employment possibilities open to the then recently graduated university students had strongly decreased. This situation resulted in a loss of talent for research groups, and it was feared that there would be a decline in the motivation and development possibilities for researchers. The developments briefly described here formed no phenomena exclusive to the Netherlands but also made their appearances in substantially all of the western countries.
Nonlinear differential equation systems of the kind used in system dynamics are capable of exhibiting highly irregular, erratic, turbulent or “chaotic” behavior. Conditions for the existence of this phenomenon are discussed and their application in dynamic socio-economic modeling explored. In particular, irregularities in economic cycles might be explained by nonlinear feedback effects in contrast to the usual “random shock” model. Dynamo simulations are used to illustrate the basic concepts involved. The view, often emphasized by Forrester, that policy should not be based on level predictions but should focus on regulating qualitative modes would seem to be strongly supported. The positive economics position associated with Friedman that theories should be judged on their predictive performance would now appear to be too restrictive. Instead, the system dynamics view that the plausibility of model assumptions should be the main basis for establishing theory credibility is strongly reinforced.
System Dynamics consists of a body of theory, philosophy, methodology, policy-related applications, and experience. Basic to system dynamics is the theory of the semi-closed, fully closed-loop system in which the feedback loop is the principal construct. In the 20 years of its existence, major emphasis has been placed on the methodology of model-building, on applications, and on philosophical debates involving alternative approaches, particularly the static econometric approach. Experience has produced improvements in the original theory. However, feedback loops are not the only constructs for dynamic theory-building, and cybernetic, self-regulating systems are not the only kinds of living systems, nor is the cybernetic perspective invariably the only or most appropriate perspective over the life history of a particular system. The processes of self-organization and the emergence of new structure deserve equal attention in the evolution of systems. This paper briefly reviews the history of system dynamics. An analysis is then made of present system dynamics theory. This is followed by summaries of three field theories—of critical phenomena, catastrophe theory, and disruptive structures—and attempts at synthesizing these theories and system dynamics. Then ways of enriching existing system dynamics models with fuller use of knowledge from behavioral/social science and sociotechnical systems, with particular relevance to the National Model, are discussed. The paper concludes with an identification of three immediate next steps in research.
There is unquestionable need for sound and disciplined methodology of experimenting with SD models. A number of valuable papers shows various ways utilizing sensitivity analysis, programming of experiments and other approaches. But should we not attack the problem more fundamentally before getting into more specific and costly analysis? We would like propose a different kind of approach, it is analysis of SD models based on experiments with families of trajectories.
Lebanon, the country is new; Lebanese society is ancient. Lebanon’s current geographic frontiers and political institutions were defined in the Constitution of 1926 and, except for slight modifications introduced on the eve of Lebanon’s independence 1943, remain in effect. The social and cultural characteristics of Lebanese society have their origins in the Phoenician, Greco-Roman, Arab, and Ottoman civilizations. The Lebanese state, with an area of ten thousand square kilometers, and Lebanese society with a resident population of three million persons (and almost an equal number of expatriates), have a significance in the Middle East and, indeed worldwide, out of proportion to their size, owing to their role as a vital link between East and West.
After twenty-five years of development and some notable achievements the field of System Dynamics is not as large, well-known, respected and influential as it should be based on the breadth and power of its principles and the need of industry and society for dynamic analysis of this kind. It is suggested that System Dynamics’ methods be used to analyze the growth of the field and improve its development. This paper initiates the self-analysis by presenting a review of performance and preliminary model structure for the field to encourage constructive criticism and to facilitate understanding and cooperative revitalization. The model structure may be general enough to apply to other fields as well.
This paper describes a System Dynamics model of the foreign trade sector in a small open economy. The model is used to investigate the consequences of various economic policies aimed at solving problems which a high-cost country may experience when its debt-ratio begins to increase. With the model, we simulate some of the economic consequences of currency devaluation, tax increase, restrictive public policy and income freeze. Each of these measures significantly improve the debt-ratio, but only after a delay of 5-8 years, as a result of various bottlenecks in the decision-making process.
The paper is organized in three parts. It begins with a brief review of the substantive exchange of views in the case, including the Company’s position, the Attorney General’s position, and the analyses and counter analyses presented in support of these positions. In Part Two, the paper describes the participants and the schedule of the hearings. It is argued that the rapid pace of these hearings and the background of the participants are important determinants of usefulness of System Dynamics models under adversary proceedings. The third part of the paper concludes with a discussion of the advantages and disadvantages of system dynamics under fast paced, adversary conditions.
The aggregate demand-aggregate supply (AD-AS) model presented in most intermediate and advanced macroeconomic texts may provide misleading insights into the effects of economic stabilization policies. Conventional analysis of the AD-AS model shows that policies which raise demand during periods of peak unemployment and reduce demand during periods of low unemployment tend to stabilize the economy. This paper: (1) Develops a dynamic model of the AD-AS model; (2) Shows that the model produces a very long period of oscillation (approximately 50 years); (3) Shows that the conventional stabilization policies increase damping of the long cycle; (4) Adds inventories to the base model; (5) Shows that the inventories introduce a business cycle fluctuation to model behavior; (6) Shows that the conventional stabilization policies destabilize the business cycle behavior mode. This paper should help explain why standard “stabilization” policies tend to destabilize the business cycle in the System Dynamics National Model.
The Causal Loop Diagram, a signed diagraph which shows the variables and interactions of a system Dynamic model, has been studied. It has been found convenient to start with the levels and their interactions. Then signed interactions between levels and rates may proceed. The transformation from signed level diagraph into Causal Loops, in terms of levels and rated, is presented. Dynamics properties such as stability, oscillations, controllability, and observability are related to the information contained in the Causal Loop Diagram. These dynamics properties have been found very useful in the synthesis of policies aimed to manipulate structure. Illustrations and examples are inserted in the exposition.
It was the purpose of this study to describe a modest theory of educational change which could be stated with some precision, which could reproduce observed historical behaviors, which could facilitate an understanding of the structural dynamics giving rise to those behaviors, and which would permit the examination of selected policies which have some historical currency.
To improve matters in the behavioral sciences, system dynamics can play the role of catalyst by providing both the holistic view which is needed to understand the behavior of human beings and not just bits and pieces of their actions and the necessary technical tools to map behavior over into manageable models. In return, system dynamicists will learn how to include a more differentiated and thus more realistic representation of human behavior in their models of social systems.
The purpose of this paper is to introduce an integrated framework for long-range strategic planning to a railroad. The framework is a computer simulation model designed to be useful to most freight –hauling railroads. The model can help to increase the understanding of problems facing the railroad and to aid in developing strategies for addressing these problems. It is designed to forecast railroad performance and to aid in developing more effective policies for railroad management. It can also be used by Federal agencies to evaluate impacts policy on railroad performance.
Since 1972, Jay Forrester and colleagues at MIT have been evolving the System Dynamics National Model (SDNM). The purpose of this model is to guide policy makers in dealing with today’s major problems. The ambitious scope of the project motivates careful examination of modeling practices and how they contribute to the success of the project. The above paper recounts incidents in the development of the SDNM and discusses the related modeling issues.
The model in this paper is, therefore, directed towards an understanding of the mechanisms at work during the UK business cycle. Its time horizon is no greater than ten years, with the main emphasis on the next five. It is frequently argued that cycles of longer period than the business cycle exist, e.g. the 50 year long wave. It is not intended that this model should try to capture in detail the mechanisms believed to produce them. However, their role in determining the underlying trend must be recognized, and their effects incorporated exogenously, perhaps by reference “off-line” to other models designed to look at these more distant horizons.
Planning and Control are essential for the success of any human endeavour and are now widely established concepts in most organizations, usually enshrined in formal corporate/planning systems. The process of planning may be analysed in a number of different ways, but generally there is a consensus on the need to split the process up into strategic planning, which directs the organization and tactical or operational planning which deals with the resource allocation for specific operational units and integrates them into the whole.