Multivariate Analysis

Abstract

Until this point we have been concerned primarily with methods for analyzing single variables obtained from twin pairs; that is, with estimation of the relevant sources of genetic and environmental variation in each variable separately. Most studies, however, are not designed to consider single variables, but are trying to understand what factors make sets of variables correlate, or co-vary, to a greater or lesser extent. Just as we can partition variation into its genetic and environmental components, so too we can try to determine how far the covariation between multiple measures is due to genetic and environmental factors. This partitioning of covariation is one of the first tasks of multivariate genetic analysis, and it is one for which the classical twin study, with its simple and regular structure, is especially well-suited.