A great deal of psychological research examines the effect a single independent variable has on a single dependent variable. However, it is perfectly reasonable to examine the effects multiple independent variables simultaneously have on a single dependent variable. Experimental designs that include multiple independent variables are known as factorial designs. They come in a wide variety including between-group and within-subject variables and a mixture of both kinds. When two or more variables in a factorial design show a statistically significant interaction, it is common to analyze the simple main effects. Simple main effects analysis typically involves the examination of the effects of one independent variable at different levels of a second independent variable.[Page 1376]
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