If you specify more than one effect, then you must separate the effects with spaces . For example, assuming A and B are listed as Class Variables , typing A B in the text field specifies variables A and B as main fixed effects .
To specify interactions between effects, type an asterisk ( * ) between the effects. For example, assuming A and B are listed as Class Variables , typing A B A*B specifies variables A and B , and the interaction between A and B as effects (a two-way ANOVA model).
A vertical bar ( | ) can be used to create main effects and interactions. For example, typing A|B is the same as typing A B A*B .
An at-sign ( @ ) can be used to limit the number of interactions. For example, typing A|B|C@2 removes the three-way interaction term.