11 Fixed, random and mixed effects
Every model so far has treated the levels of each factor as fixed: chosen deliberately, the only ones of interest, and the subject of all conclusions. Often the levels are instead a sample from a larger population: batches of raw material, operators, machines, days, locations. Nobody wants to know whether batch \(3\) was better than batch \(5\), since neither will be used again; the question is how much batches vary. Such a factor is random, its effects are random variables, and the parameters of interest are variances. This section develops the analysis of random and mixed models for balanced data.
11.1 Fixed and random factors
11.2 The one-way random effects model
11.3 The two-factor random effects model
11.4 The two-factor mixed model
11.5 Expected mean squares in general
11.6 Practice problems
11.2 The one-way random effects model
11.3 The two-factor random effects model
11.4 The two-factor mixed model
11.5 Expected mean squares in general
11.6 Practice problems
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