Transcription of Chapter 15 Mixed Models - CMU Statistics
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Chapter 15 Mixed Models - CMU Statistics
Chapter 15 Mixed ModelsA flexible approach to correlated OverviewCorrelated data arise frequently in statistical analyses. This may be due to group-ing of subjects, , students within classrooms, or to repeated measurements oneach subject over time or space, or to multiple related outcome measures at onepoint in time. Mixed model analysis provides a general, flexible approach in thesesituations, because it allows a wide variety of correlation patterns (or variance-covariance structures) to be explicitly mentioned in Chapter 14, multiple measurements per subject generally resultin the correlated errors that are explicitly forbidden by the assumptions of standard(between-subjects) AN(C)OVA and regression Models . While repeated measuresanalysis of the type found in SPSS, which I will call classical repeated measuresanalysis , can model general (multivariate approach) or spherical (univariate ap-proach) variance-covariance structures, they are not suited for other explicit struc-tures.
random e ects the correlation of these various e ects may need to be speci ed. To run a mixed model, the user must make many choices including the nature of the hierarchy, the xed e ects and the random e ects. In almost all situations several related models are considered and some form of model selection must be used to choose among related models.
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