Circumscribing System Dynamics Modeling and Building Confidence in Models a Personal Perspective

Abstract

While there is a consensus among system dynamics scholars that the dichotomous term validity must be replaced by the term confidence for system dynamics models, it is unclear what qualifies as a system dynamics model – a computational instrument for forecasting, or an experimental tool to inform the policy process? And what exactly needs to be done to build confidence in a model? Confidence building process is described in the system dynamics writings at a rather philosophical level that can be used to justify almost any model. The confidence building procedures provided in the text books are sketchy, do not distinguish between forecasting and policy models and do not adequately describe the iterative process subsumed in the various steps of model construction that might yield confidence. Confidence in forecasting models is an article of faith no matter how detailed they might be and how diligent is their calibration. Forecasting models are albeit irrelevant to system dynamics practice, which must focus on policy. This paper revisits the problem of confidence in system dynamics models addressing policy and attempts to carefully describe their qualification and the process that practitioners must follow to arrive at them.