Model Assumptions and Boundary Judgment: What Systems Models Include and Exclude
Model assumptions and boundary judgment examine the hidden choices that determine what a systems model includes, excludes, simplifies, measures, and communicates. This article explains why assumptions are not minor technical details but part of the model’s structure, credibility, and ethical meaning. It covers structural, causal, parameter, data, behavioral, scenario, scale, measurement, boundary, and normative assumptions, showing how each can shape model outputs before analysis begins. Readers will learn how boundary choices affect system visibility, stakeholder representation, uncertainty, validation, sensitivity analysis, and responsible interpretation. The article also explains assumption registers, exclusion logs, boundary critique, evidence strength, and boundary sensitivity testing. The central argument is that useful models are not assumption-free; they are transparent about what they assume, honest about what they exclude, disciplined about testing fragile claims, and careful about where model conclusions should and should not be applied publicly.









