Random Effects (Mixed Model)

Click the Random factors button on the Quick Specs Dialog - Options tab or the Analysis Wizard Extended Options - Advanced tab to display the Random Effects (Mixed Model) dialog box.

Specify random. Select the factors that are to be treated as random effects in the design in the Specify random box. Select multiple factors by holding down the CTRL key while clicking on the respective factors; select a list of consecutive factors by dragging the mouse over the list.

OK. Click the OK button to return to the Quick Specs Dialog - Options tab or the Analysis Wizard Extended Options - Advanced tab after specifying the random effects.

Cancel. Click the Cancel button to return to the Quick Specs Dialog - Options tab or the Analysis Wizard Extended Options - Advanced tab; any changes made are disregarded.

Note that all effects involving random effects will also be treated as random effects in the analysis. For details concerning mixed models (designs with random effects), see the Mixed-model ANOVA and ANCOVA topic in the Introductory Overview section; see also the Variance Components and Mixed Model ANOVA/ANCOVA module).

Fixed and random effects differ in that the levels for fixed effects are especially selected or "fixed" by the researcher (e.g., manipulation in an experiment), whereas the levels for random effects are selected by the researcher via some random selection procedure from a population of possible levels (e.g., three different schools in which an experiment was conducted).

See General ANOVA/MANOVA and GLM Notes - Random Effects for additional details.