Abstract for: Is Velocity Stock or Flow? A Note on Model Formulation
Textbooks do not provide a clear guideline for the model formulation phase of system dynamics modeling, especially for identifying stocks and flows. Some resources even suggest that a variable type can change depending on the topic at hand. A classic example is "velocity," which, according to some, can be modeled as flow if the question is distance or as stock if the question is dynamics of velocity due to changes in acceleration. This paper argues that it is better for quality control, modeling standardization, and educational purposes that we provide a restrictive guideline for model formulation by creating clear rules for identifying stocks and flows in a model. To this end, stock and flow definitions and identification tests are revised and compiled as a new method. A systematic procedure is also offered to facilitate the use of the proposed method.