Effects are specified with a special notation using variable names and operators. A third operator, the bar operator , is used to simplify effect specification.
Class variables can be either numeric or character .
For example, the heights and weights of subjects are continuous variables. There are seven different types of effects used in the GLM procedure. This example contains crossed continuous terms by crossed classification terms nested within more than one class variable. The continuous list comes first, followed by the crossed list, followed by the nesting list in parentheses. Note that asterisks can appear within the nested list but not immediately before the left parenthesis.