ABSTRACT
Guastello ( Guastello, 1995) noted that only the man-made part of the physical world consists of straight lines: “Look out the window. Is there a straight line there that wasn't man-made?” (p. 1). Researchers appear to exhibit the same type of bias. Guastello continues: “Why do social scientists insist on describing human events as if all the rules that make those events occur are based on straight lines?” (p. 1). Undoubtedly, the behavioral world is at least as nonlinear as the physical world, although research methodology typically starts with linear models (and often ends there as well). This paper, as well as others in this volume, will apply nonlinear dynamic models to processes that are themselves naturally nonlinear and dynamic. As we described in Rodgers, Rowe, and Buster (1998b, p. 1096): “These models are called dynamic because they model the change in some phenomenon over time. . . . The models are called nonlinear because the outputs of the model . . . are not linearly proportional to the inputs.”
