Use the Random 1 tab to add random effects to the model. Random effects are built using classification variables, regressors/covariates variables, and operator buttons.
The Repeated tab is used to specify the R matrix in the mixed model. The Repeated tab is also used to specify covariance structures for repeated measurements on subjects. If no repeated statement is specified, R is assumed to be equal to s2I. The repeated effect must contain only classification variables.
Note: The same variable cannot be used in both the fixed effects specification and the random effects specification unless it is used differently, such as part of a product. The same term (single variables, products, or nested variables) must not appear in both specifications.
Drag variables from the boxes on the left to the fields in the tab and click the operator buttons to build the model or type the names and operators directly in the fields.
Operators:
+ addition (not available in Repeated tab or when specifying variance blocking or group variables),
* multiplication,
( ) parentheses for indicating nested variables in the model.
Fields:
Variance Blocking Variables (Subject): Optionally identify subjects in a dataset. If specified, must be a classification model term built from items in the Classification Variables box. Complete independence is assumed among subjects, so the subject variable produces a block diagonal structure with identical blocks.
Group: Optionally define an effect specifying heterogeneity in the covariance structure. If specified, must be a classification model term built from items in the Classification Variables box. All observations with the same level of group effect have the same covariance parameters. Each new level of the group effect produces a new set of covariance parameters with the same structure as the original group.
(Random 1 tab only) Check the Random Intercept box to include a random intercept. Commonly used when a subject is specified in the Variance Blocking Variables (Subject) field. The default setting is no random intercept.
If the model contains random effects, a covariance structure type must be selected from the Type menu.
If Banded Unstructured (b), Banded No-Diagonal Factor Analytic (f), or Banded Toeplitz (b) is selected, set the Number of bands(b) (default is 2). The number of bands (or factors, depending on the covariance structure type) corresponds to the dimension parameter.
Press Add Random to add other variance models or press Delete Random to delete a variance model.
For explanations of covariance structure types, see the “Covariance structure types in the Linear Mixed Effects object” section.
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