LOCATION Subcommand (PLUM command)

The LOCATION subcommand specifies the location model.

  • Specify a list of terms to be included in the location model, separated by commas or spaces.
  • The default location model is generated if the subcommand is not specified or empty. The default model contains the intercept, all of the covariates (if specified) in the order in which they are specified, and all of the main factorial effects in the order in which they are specified on the variable list.
  • To include the intercept term explicitly, enter the keyword INTERCEPT on the subcommand.
  • To include a main effect term, enter the name of the factor 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. The keyword INTERCEPT cannot be used to construct an interaction term.
  • 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.

Example

PLUM
  chist  BY numcred othnstal
  /CRITERIA = CIN(95) DELTA(0) LCONVERGE(0) MXITER(100) MXSTEP(5)
              PCONVERGE(0)
  /LOCATION = numcred othnstal numcred*othnstal.
  • LOCATION specifies that the location model consists of numcred, othnstal, and their interaction effect.