User Guide

49
Linear Mixed Models
Linear Mixed Models Random Effects
Figure 4-4
Linear Mixed Models: Random Effects dialog box
Random Effects. There is no default model, so you must explicitly specify the random
effects. Alternatively, you can build nested or non-nested terms. You can also choose
to include an intercept term in the random-effects model.
You can specify multiple random-effects models. After building the first model, click
Next to build the next model. Click Previous to scroll back through existing models.
Each random-effect model is assumed to be independent of every other random-effect
model; that is, separate covariance matrices will be computed for each. Terms specified
in the same random-effect model can be correlated.
Covariance type. This allows you to specify the covariance structure for the random-
effects model. A separate covariance matrix is estimated for each random effect. The
available structures are as follows: