Mixed model designs are an extension of the general linear model, as in analysis of variance (ANOVA) designs. There is no common term for the mixed model design. Researchers sometimes refer to split-plot designs, randomized complete block, nested, two-way mixed ANOVAs, and certain repeated measures designs as mixed models. Also, mixed model designs may be restrictive or nonrestrictive. The restrictive model is used most often because it is more general, thus allowing for broader applications. A mixed model may be thought of as two models in one: a fixed-effects model and a random-effects model. Regardless of the name, statisticians generally agree that when interest is in both fixed and random effects, the design may be classified as a mixed model. Mixed model analyses are used ...