MODEL Subcommand (CSLOGISTIC command)

The MODEL subcommand is used to specify the effects to be included in the model. Use the INTERCEPT subcommand to control whether the intercept is included.

• The MODEL subcommand defines the cells in a design. In particular, cells are defined by all of the possible combinations of levels of the factors in the design. The number of cells equals the product of the number of levels of all the factors. A design is balanced if each cell contains the same number of cases. CSLOGISTIC can analyze balanced and unbalanced designs.
• The format is a list of effects to be included in the model, separated by spaces or commas.
• If the MODEL subcommand is not specified, CSLOGISTIC uses a model that includes the intercept term (unless it is excluded on the INTERCEPT subcommand), main effects for any factors, and any covariates.
• To include a term for the main effect of a factor, enter the name of the factor.
• To include a term for an interaction between factors, use the keyword BY or the asterisk (*) to join the factors that are involved in the interaction. For example, A*B means a two-way interaction effect of A and B, where A and B are factors. A*A is not allowed because factors that are inside an interaction effect must be distinct.
• To include a term for nesting one effect within another effect, use a pair of parentheses. For example, A(B) means that A is nested within B. 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.
• Multiple nesting is allowed. For example, A(B(C)) means that B is nested within C, and A is nested within B(C).
• Interactions between nested effects are not valid. For example, neither A(C)*B(C) nor A(C)*B(D) is valid.
• To include a covariate term in the design, enter the name of the covariate.
• Covariates can be connected, but not nested, through the * operator to form another covariate effect. Interactions among covariates such as X1*X1 and X1*X2 are valid, but X1(X2) is not.
• Factor and covariate effects can be connected only by the * operator. Suppose A and B are factors, and X1 and X2 are covariates. Examples of valid factor-by-covariate interaction effects are A*X1, A*B*X1, X1*A(B), A*X1*X1, and B*X1*X2.