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Though the concept of ‘stylized fact’ plays an important role in the economic literature, there is little analysis of the definition and evaluative use of the term. A permissive account of stylized facts is developed which focuses on their mediating role between models and empirical evidence. The mediation relationship restricts stylized facts by requiring concrete empirical targets. On the other hand, there is much legitimate diversity within the permissive account; key dimensions of diversity are argued to be the part of the model targeted (explanans vs. explanandum) and degree of partiality of correspondence. The use of stylized fact in model evaluation points to the downside of stylization: decreased ability to support strong claims about particular targets. In the final analysis, the role of stylized facts in model-based explanation depends on the view taken of the relative importance of generality and empirical adequacy.

Modularity is an important concept in evolutionary theorizing but lack of a consistent definition renders study difficult. Using the generalized NK-model of fitness landscapes, we differentiate modularity from decomposability. Modular and decomposable systems are both composed of subsystems, but in the former, these subsystems are connected via interface standards, while in the latter, subsystems are completely isolated. We derive the optimal level of modularity, which minimizes the time required to globally optimize a system, both for the case of two-layered systems and for the general case of multi-layered hierarchical systems containing modules within modules. This derivation supports the hypothesis of modularity as a mechanism to increase the speed of evolution. Our formal definition clarifies the concept of modularity and provides a framework and an analytical baseline for further research.