Online Content

4931. Randers, Jørgen, "System Dynamics: A Tool for Broad Policy Analysis"

Type:
Document
Date Created:
1976
Collection:
System Dynamic Society Records
Collecting Area:
University Archives
Collection ID:
ua435
Parent Record(s):
23d738ba88f8333bc39725f9cb5bd0b8, 7f4e0cd9dcbf7a3743e13c4911e77bc2, and dbb17ec8affa7ecbcd419a760cb61093
Thumbnail Path Ss:
/downloads/hh63td14j?file=thumbnail
System Modified Dtsi:
2020-01-02T18:34:40Z
Description:
Industrialized societies are presently characterized by rapid change, strong interactions and an abundance of new phenomena. To increase the likelihood of policies having the intended effects, there is a need for policy analysis with a broader perspective and longer time horizon. The main task in such broad policy analysis should be to integrate the vast amount of available information into a useful conceptual structure of the problem area. System Dynamics (SD) –relying heavily on descriptive information for a data base, on a theory of the structure of social systems for theory formation, and on computer simulation for relating structure to behaviour—offers one method of attaining such broad policy analysis. This paper reviews the historical development of the field and examines the major system dynamics literature. The impatient questions of “what is?”, “why does one do?”, “when should one do?”, and “how does one do SD?” are all answered in summary fashion. Within the system dynamics profession, intense conflicts abound as to what constitutes “proper procedure” for the policy analysis process, particularly concerning model conceptualization and testing. Much disagreement arises from implicit differences in modeling objectives. Explicit recognition of objectives and procedures could reduce much of the conflict.

4932. Rahn, R. Joel, "Delays and Aggregation in System Dynamics Model"

Type:
Document
Date Created:
1976
Collection:
System Dynamic Society Records
Collecting Area:
University Archives
Collection ID:
ua435
Parent Record(s):
23d738ba88f8333bc39725f9cb5bd0b8, 7f4e0cd9dcbf7a3743e13c4911e77bc2, and dbb17ec8affa7ecbcd419a760cb61093
Thumbnail Path Ss:
/downloads/pz50hd740?file=thumbnail
System Modified Dtsi:
2020-01-02T18:34:39Z
Description:
This paper focuses on the aggregation that is implicit in the use of distributed delays in dynamic models. The aggregation process relates the continuous time-dependent response of a delay structure to the underlying distribution of delay times of the disaggregated events which constitute the delay. The discussion covers in particular the special case of exponential delays used in system dynamics models.

4933. Phillips, W. G. B., "Monte Carlo Tests of Conclusion Robustness"

Type:
Document
Date Created:
1976
Collection:
System Dynamic Society Records
Collecting Area:
University Archives
Collection ID:
ua435
Parent Record(s):
23d738ba88f8333bc39725f9cb5bd0b8, 7f4e0cd9dcbf7a3743e13c4911e77bc2, and dbb17ec8affa7ecbcd419a760cb61093
Thumbnail Path Ss:
/downloads/hm50v9152?file=thumbnail
System Modified Dtsi:
2020-01-02T18:34:38Z
Description:
Conclusions derived from world models have little value if they do no include an estimate of the uncertainty associated with the outputs. This paper describes the System Analysis Research Unit World Model and gives an account of the application of Monte Carlo techniques to testing the model. Samples of uncertain data encoded in probability densities are used as input for model runs. The model output is analysed statistically and the contribution to total uncertainty by the variance of the inputs is determined. The output is also to be additive over a limited range. Due to the strong negative feedback loops in the model, the model usually attenuates any variation in inputs. The cost of Monte Carlo methods is justified by the quality of the results obtained.

4934. Nilsson, Jan-Evert, "A Framework for Understanding Social Phenomena"

Type:
Document
Date Created:
1976
Collection:
System Dynamic Society Records
Collecting Area:
University Archives
Collection ID:
ua435
Parent Record(s):
23d738ba88f8333bc39725f9cb5bd0b8, 7f4e0cd9dcbf7a3743e13c4911e77bc2, and dbb17ec8affa7ecbcd419a760cb61093
Thumbnail Path Ss:
/downloads/1g05fw27q?file=thumbnail
System Modified Dtsi:
2020-01-02T18:34:37Z
Description:
In this report we discuss our possibilities to attain insight about social phenomena. In the first part of the report we argue the nature of social phenomena is different from natural phenomena. Therefore there is a danger connected with the fact that social science for so long time has been dominated by techniques and goals which were successfully developed for the purpose of natural science. In the second part of the report we identify and discuss four essential problems in the study of social phenomena. The problems are: (a) the definition problem, (b) the issue of limitation, (c) the problem of causality and (d) the problem of stability. In the last part of the report we discuss in what way social phenomena can be understood. Six conditions for a successful paradigm in social science are presented and we can conclude that used in a proper way System Dynamics can be one paradigm that fulfill these conditions.

4935. Meadows, Donella H., "The Unavoidable A Priori"

Type:
Document
Date Created:
1976
Collection:
System Dynamic Society Records
Collecting Area:
University Archives
Collection ID:
ua435
Parent Record(s):
23d738ba88f8333bc39725f9cb5bd0b8, 7f4e0cd9dcbf7a3743e13c4911e77bc2, and dbb17ec8affa7ecbcd419a760cb61093
Thumbnail Path Ss:
/downloads/8w32rq04w?file=thumbnail
System Modified Dtsi:
2020-01-02T18:34:36Z
Description:
This paper is a summary of the major assumptions underlying the field of computer modeling and the specific assumptions that differentiate four modeling methods used to represent social systems: system dynamics, econometrics, input-output analysis, and optimization. The primary conclusions are: 1. Each modeling method is based on a set of techniques and priors that suit it well to some sorts of policy problems and poorly to others. 2. Misunderstandings between different kinds of modelers and between modelers and clients often arise from failures to recognize these implicit priors and the various strengths and weaknesses of the various modeling schools. 3. Some modeling schools, especially system dynamics and econometrics, are based on such different basic world views and assumptions about the nature of human knowledge that communication from one school to another is almost impossible.

4936. Mass, Nathaniel J. with Peter M. Senge, "Alternative Tests for the Selection of Model Variables"

Type:
Document
Date Created:
1976
Collection:
System Dynamic Society Records
Collecting Area:
University Archives
Collection ID:
ua435
Parent Record(s):
23d738ba88f8333bc39725f9cb5bd0b8, 7f4e0cd9dcbf7a3743e13c4911e77bc2, and dbb17ec8affa7ecbcd419a760cb61093
Thumbnail Path Ss:
/downloads/j6731m78w?file=thumbnail
System Modified Dtsi:
2020-01-02T18:34:35Z
Description:
This paper contrasts two approaches to testing the importance of model variables: single-equation statistical tests and model-behavior tests. The paper demonstrates that, both theoretically and operationally, tests which analyze the impact of individual variables on model behavior are better suited to the task of selecting model variables. Conversely, the statistical tests should not be viewed as tests of model specification per se, but as tests of a particular type of data usefulness. When viewed as tests of data usefulness, the statistical tests have a clear, albeit quite narrow, role in model validation: they warn the modeler when available data do not permit accurate estimation of model parameter. However, as a detailed example illustrates, a model relationship may be difficult to estimate yet extremely important for overall model behavior.

4937. Mass, Nathaniel J., "Stock and Flow Variables and the Dynamics of Supply and Demand"

Type:
Document
Date Created:
1976
Collection:
System Dynamic Society Records
Collecting Area:
University Archives
Collection ID:
ua435
Parent Record(s):
23d738ba88f8333bc39725f9cb5bd0b8, 7f4e0cd9dcbf7a3743e13c4911e77bc2, and dbb17ec8affa7ecbcd419a760cb61093
Thumbnail Path Ss:
/downloads/pc28b212p?file=thumbnail
System Modified Dtsi:
2020-01-02T18:34:34Z
Description:
This paper contrast two viewpoints for analyzing the concepts of supply and demand. The first viewpoint, which dominates most economic thinking, treats supply and demand as rates of flow. For example, supply in economic models tends to be measured by a rate of production, while demand is measured by a flow of consumption or purchases. The second viewpoint sees supply and demand primarily as stock variables or integrations. According to this viewpoint, for example, supply would be measure by the available inventory of a commodity while demand would be measured by a backlog of unfilled orders. The central point of the paper is that stock-variable concepts of supply and demand must be incorporated explicitly in economic models in order to capture the full range of disequilibrium behaviour characteristics of real socio-economic systems. More specifically, the paper shows that consideration of stock-variable measures of supply and demand is necessary to describe the price- and quantity-adjustment mechanisms linking supply and demand; to analyze properly the stability characteristics of an economic systems; to analyze short-run and long-run disequilibrium behaviour; and to assess the desirability of economic policies intended to influence such disequilibrium modes behaviour as economic growth and fluctuation.

4938. Low, Gilbert W., "The Principle of Conservation and the Multiplier-Accelerator Theory of Business Cycles"

Type:
Document
Date Created:
1976
Collection:
System Dynamic Society Records
Collecting Area:
University Archives
Collection ID:
ua435
Parent Record(s):
23d738ba88f8333bc39725f9cb5bd0b8, 7f4e0cd9dcbf7a3743e13c4911e77bc2, and dbb17ec8affa7ecbcd419a760cb61093
Thumbnail Path Ss:
/downloads/h989rm427?file=thumbnail
System Modified Dtsi:
2020-01-02T18:34:33Z
Description:
The principle of conservation states that physical quantities are confined to their own identifiable channels and can enter, circulate within, or depart from a system only by explicit processes. This paper applies the conservation principle to an analysis of the multiplier-accelerator theory of business cycles. Section I describes and critiques a well-known model of the multiplier-accelerator interaction. By ignoring accumulations of inventory and fixed capital investment, the model fails to observe the conservation of important physical flows. Section II proposes a system dynamics model that incorporates the multiplier and accelerator processes within a closed, conserved-flow framework. Section III uses computer simulation to portray the impact of conservation on the multiplier-accelerator interaction. Simulations of the system dynamics model reveal plausible long-term cycles, rather than the short-term fluctuation associated with traditional multiplier-accelerator models. At the end of Section III, the model is modified to account explicitly for labor, as well as capital, in the production process. This revised model produces both short-term and long-term oscillation when submitted to a noise input. The short-term oscillations, averaging about 5 years, reflect the attempt to adjust inventories by varying the labor input to production. The longer fluctuations in capital stock, averaging 19 years, reflect the management of investment in fixed capital. In all of the tests, the incorporation of conserved flows considerably reduces the sensitivity of system behavior to changes in parameter values. The simulations provide theoretical evidence for divorcing short-term business cycles from the interaction of the multiplier and accelerator.

4939. Lied, Finn, "Social Difficulties Versus Social Problems"

Type:
Document
Date Created:
1976
Collection:
System Dynamic Society Records
Collecting Area:
University Archives
Collection ID:
ua435
Parent Record(s):
23d738ba88f8333bc39725f9cb5bd0b8, 7f4e0cd9dcbf7a3743e13c4911e77bc2, and dbb17ec8affa7ecbcd419a760cb61093
Thumbnail Path Ss:
/downloads/34850069t?file=thumbnail
System Modified Dtsi:
2020-01-02T18:34:32Z
Description:
The opening address at the 1976 International Conference on System Dynamics points out that today's social ills are diffuse difficulties rather than clear-cut problems. Remedial action must start with attempts to clarify the problem, and develop alternative comprehensive strategies that consider a wide segment of society and also the long-term future in an open minded fashion. System Dynamics may serve as a tool for broad policy analysis of this kind.

4940. Krallmann, Hermann, "The Integration of Alternative Modelling with Dynamo"

Type:
Document
Date Created:
1976
Collection:
System Dynamic Society Records
Collecting Area:
University Archives
Collection ID:
ua435
Parent Record(s):
23d738ba88f8333bc39725f9cb5bd0b8, 7f4e0cd9dcbf7a3743e13c4911e77bc2, and dbb17ec8affa7ecbcd419a760cb61093
Thumbnail Path Ss:
/downloads/sb397t15t?file=thumbnail
System Modified Dtsi:
2020-01-02T18:34:31Z
Description:
Often system dynamics, and particularly the DYNAMO- language, is attacked for not integrating other modelling approaches into the field. This investigation offers alternatives that will hopefully stand up against the critics. The first part of this paper concerns the integration of external functions into system dynamics models. Modifications of the DYNAMO simulation language and of the DYNAMO compiler are explained, and conceptional questions about the integration are discussed. By means of examples of LP programs and statistical methods, the paper shows the philosophical improvements entailed by the system dynamics method.The same criteria are applied in the second part of this paper to the model-method integration of a system dynamics model with an input-output method, considered to be representative of a complete economic structure.The last part of the paper explains the integration of system dynamics model into the higher program structure of an optimizing feedback loop. The best combination of input vector parameters is calculated in the feedback loop at any time so that the output vector follows a predetermined objective function. The overall paper contents demonstrate the flexibility of the system dynamics method.