Model formulation: What experts think about and when

Model formulation is a critical craft skill that deserves more attention from OR practitioners and educators. As a step toward understanding how experts formulate OR models, I conducted an experiment in which twelve skilled analysts generated think-aloud protocols while working model formulation exercises 60 minutes long. The coded transcripts tracked the modelers' attention to five topics corresponding to stages in the usual OR paradigm: problem context and model structure, realization, assessment, and implementation. Analysis of the transcripts yielded these conclusions: topics other than structure attracted a significant proportion of modelers' attention; modelers frequently switched their attention among the topics; the switching was usually an alternation between structure and the other topics, especially assessment; on average, the modelers progressed through the topics in the given order; there was limited support for the notion of modeler-specific and problem-specific effects influencing the attention given to each topic; and there was support for the idea of individual modeling styles.