Workspace Node: GLM Custom Design - Results - Planned Comps Tab

In the GLM Custom Design node dialog box, under the Results heading, select the Planned Comps tab to access options to perform a priori (planned) comparisons between the means in the design. A discussion of the rationale and applications of planned comparisons and post-hoc tests is provided in the Contrast analysis and post-hoc tests section in the context of the ANOVA/MANOVA module. Note that these options are only available if the current design contains effects for categorical predictor variables or within subject (repeated measures) effects.

Note: planned (a priori) comparisons (contrast analysis). A priori planned comparisons are usually performed after an analysis involving effects for categorical predictor variables has yielded significant effects. The purpose of planned comparisons then is to determine whether the pattern of means for the respective effect follows the one that was hypothesized, that is, you compare the specific means for the effect of interest that were hypothesized to be different from each other (e.g., in a 3-level effect Group, you might test whether the mean for level 1 is significantly different from the mean for level 3). Statistica GLM provides a convenient user-interface for specifying contrast coefficients; these coefficients are then used to compare the least squares means (see also the Means tab) for the respective chosen Effect. Thus, the contrasts for the planned comparisons are applied to the means predicted by the current model; these means are identical to the observed unweighted means in the case of full factorial designs without continuous predictors (covariates).
Note: random effects. The error terms for all planned comparisons will always be computed from the sums of squares residuals. Those error terms may not be appropriate, and when random effects are involved, you should interpret the results of planned comparisons with caution.
Element Name Description
Effect Select the desired effect from all of those effects in the current design in the Effect drop-down box. A priori planned comparisons are performed on the marginal means (least squares, see below) for effects involving only categorical predictor variables.
Planned comparisons of LS means Use the options in this group box to compute planned comparisons of the least squares means for the current model.
Specify contrast for LS means for selected effect Enter the contrast coefficients for the current Effect. When there are continuous predictors (covariates) in the model, the least squares means used in the comparison are computed from the covariates at their means (regardless of the selection in the Covariate values group box on the Means tab).
Display least squares means Select this check box to create a spreadsheet with the least squares means for the currently selected Effect; see also the Means tab.
Compute Select this check box to produce three spreadsheets: the Between contrast coefficients spreadsheet, Contrast estimates spreadsheet, and the Univariate or Multivariate test of significance for planned comparisons spreadsheet.
Multivariate tests Use the options in this group box to select the specific multivariate tests statistics that are to be reported in the respective results spreadsheets. For a description of the different multivariate tests statistics, refer to the Multivariate designs topic. These options are only available if the current design is multivariate in nature, i.e., if there are multiple dependent measures, or a within-subject (repeated measures) design with effects that have more than 2 levels (and hence, multivariate tests for those effects can be computed).

Options / C / W. See Common Options.

OK Click the OK button to accept all the specifications made in the dialog box and to close it. The analysis results will be placed in the Reporting Documents node after running (updating) the project.