collection={{collection-1} <, {collection-2}, ...>}

defines a set of variables that are treated as a single effect that has multiple degrees of freedom. The collection value can be one or more of the following:details=TRUE | FALSEwhen set to True, requests a table that shows additional details that are related to this effect.DefaultFALSE* name="string"specifies the name of the effect.* vars={"variable-name-1" <, "variable-name-2", ...>}&nbsp;specifies a set of variables that are treated as a single effect that has multiple degrees of freedom. The columns in the design matrix that are contributed by a collection effect are the design columns of its constituent variables in the order in which they appear in the definition of the collection effect.