4 The Elements of a Model: Causes of Variation

No model is built in isolation. Rather it is built upon a foundation of what is either already known or what might be a matter for fertile conjecture. Part of the difficulty, but also the intrinsic appeal, of genetic epidemiology is the fact that it seeks either to distinguish between major sets of theoretical propositions, or to integrate them into an overall framework. From biology, and especially through knowledge of genetics, we have a detailed understanding of the intricacies of gene expression. From the behavioral and social sciences we have strong proposals about the importance of the environment, especially the social environment, for the development of human differences. One view of our task is that it gives a common conceptual and mathematical framework to both genetic and environmental theories so that we may decide which, if any, is more consistent with the facts in particular cases.