SCALE Subcommand (PLUM command)

The SCALE subcommand specifies the scale component in the model.

  • Specify a list of terms to be included in the model, separated by commas or spaces.
  • The model will have no scale component if the subcommand is omitted.
  • No scale component is generated if the subcommand is not specified or empty.
  • To include a main effect term, enter the name of the factor on the subcommand.
  • The keyword INTERCEPT is not allowed on the subcommand.
  • To include an interaction effect term among factors, use the keyword BY or the asterisk (*) to join factors involved in the interaction. For example, A*B*C means a three-way interaction effect of A, B, and C, where A, B, and C are factors. The expression A BY B BY C is equivalent to A*B*C. Factors inside an interaction effect must be distinct. Expressions such as A*C*A and A*A are invalid.
  • To include a nested effect term, use the keyword WITHIN or a pair of parentheses on the subcommand. For example, A(B) means that A is nested within B, where A and B are factors. The expression A WITHIN B is equivalent to A(B). Factors inside a nested effect must be distinct. Expressions such as A(A) and A(B*A) are invalid.
  • Multiple level nesting is supported. For example, A(B(C)) means that B is nested within C, and A is nested within B(C). When more than one pair of parentheses is present, each pair of parentheses must be enclosed or nested within another pair of parentheses. Thus, A(B)(C) is not valid.
  • Nesting within an interaction effect is valid. For example, A(B*C) means that A is nested within B*C.
  • Interactions among nested effects are allowed. The correct syntax is the interaction followed by the common nested effect inside the parentheses. For example, interaction between A and B within levels of C should be specified as A*B(C) instead of A(C)*B(C).
  • To include a covariate term in the model, enter the name of the covariate on the subcommand.
  • Covariates can be connected, but not nested, using the keyword BY or the asterisk (*) operator. For example, X*X is the product of X and itself. This is equivalent to a covariate whose values are the square of those of X. On the contrary, X(Y) is invalid.
  • Factor and covariate effects can be connected in many ways. No effects can be nested within a covariate effect. Suppose A and B are factors, and X and Y are covariates. Examples of valid combination of factor and covariate effects are A*X, A*B*X, X(A), X(A*B), X*A(B), X*Y(A*B), and A*B*X*Y.