4 Tracing Rules of Path Analysis

One of the greatest advantages of path diagrams is their foundation upon standard rules for reading paths, called ``tracing rules,'' which yield the expected variances and covariances among the variables in the diagram. In this section we first describe the tracing rules for standardized variables, following Wright's (1934, 1968) development of the method, and then outline the rules for unstandardized variables. Although nearly all path diagrams may be traced using rules for unstandardized variables, we present path derivations for standardized and unstandardized variables separately because the former are much easier to trace than the latter, and because rules for unstandardized variables are fairly simple generalizations of the principles used in tracing paths between standardized variables. An excellent resource for learning tracing rules is the program RAMPATH (McArdle and Boker, 1990), which has a `draw_bridges' command that illustrates the rules for any model.