Generalized Linear Model (GLM) Unique Features - Post-Hoc Tests for Repeated Measures Effects
Many (but not all) of the widely used implementations of the general linear model will provide facilities for computing post-hoc comparisons of observed means; however, typically, those facilities are limited to main effects only, and only to effects for the between-group factors. In practice, however, unexpected results often occur in complex factorial design, and in particular in the interaction effects; also unexpected patterns of means will often be found in designs with one or more repeated measures factors. STATISTICA GLM includes options for performing post-hoc comparisons on the observed means in interaction effects; for effects involving repeated measures factors or interaction effects for repeated measures factors and between-group factors, GLM allows the user to choose between different possible estimates of the population error variance (sigma, which is necessary to compute the post-hoc p values). Specifically, by default, in interaction effects involving both between and within-subject (repeated measures) effects, the program will choose either (1) the between error term for comparisons of means within the levels of the repeated measures factors, (2) the respective within error term for comparisons of means within the levels of the between factors, and (3) a pooled estimate derived from both for comparisons of means across the levels of the between and within (repeated measures) factors. These methods are described in detail in Winer, Brown, and Michels (1991, p. 526-531), and Milliken and Johnson (1992, p. 322-350). An option is also provided for entering a user-defined estimate of sigma. Refer also to the description of the Error term options on the Post-Hoc tab .
Some Unique Features and Facilities of GLM