GLM repeated measure is a statistical technique that takes a dependent, or criterion variable, measured as correlated, non-independent data. Commonly used when measuring the effect of a treatment at different time points. The independent variables may be categorical or continuous. GLM repeated measure can be used to test the main effects within and between the subjects, interaction effects between factors, covariate effects and effects of interactions between covariates and between subject factors. GLM repeated measures in SPSS is done by selecting “general linear model” from the “analyze” menu. From general linear model, select “repeated measures” and then preform “GLM repeated measures.
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The within-subject factor: the basic factor for the repeated measurements. This factor in GLM repeated measure carries certain levels. The within-subjects factor will have as many levels as there are repetitions (e.g., time 1, time 2, time 3, etc.).
Covariates: quantitative independent variables.
Bartlett’s test of sphericity test: This will indicate if the factor model is inappropriate or not by determining whether or not the correlation matrix is an identity matrix.
Levene’s test: tests whether the variability is homogeneous or not.
Residual Plot: this shows the difference between the calculated and measured values of the dependent variables. A plot with excessive different trends will usually indicate an inappropriate model.
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