ABSTRACT
Most experiments combine elements of fixed effects and random effects models. This chapter introduces two-way mixed effects models, with a general treatment. Many models contain both fixed and random effects in addition to random error. Usually mixed models have a factorial arrangement, with one or more main effects being random and one or more main effects being fixed. The guiding principle for mixed models is to deal separately with the fixed and random parts of the model. The fixed part of the model is composed of main effects and any of their interactions deemed to be present. Quadratic forms appropriate to these have expected mean squares whose distribution may depend on one or more variance components from the random part. Interactions involving random effects are assumed to be random effects. Thus the only fixed effects interactions are those involving fixed main effects.
