SPSS® 12.0 Command Syntax Reference

DESIGN Subcommand
GLM: Univariate 671
DESIGN specifies the effects included in a specific model. The cells in a design are defined
by all of the possible combinations of levels of the factors in that 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. GLM can analyze both balanced and unbalanced designs.
• Specify a list of terms to be included in the model, separated by spaces or commas.
• The default design, if the DESIGN subcommand is omitted or is specified by itself, is a design
consisting of the following terms in order: the intercept term (if INTERCEPT=INCLUDE
is specified), next the covariates given in the covariate list, and then the full factorial model
defined by all factors on the factor list and excluding the intercept.
• To include a term for the main effect of a factor, enter the name of the factor on the
DESIGN subcommand.
• To include the intercept term in the design, use the keyword INTERCEPT on the DESIGN
subcommand. If INTERCEPT is specified on the DESIGN subcommand, the subcommand
INTERCEPT=EXCLUDE is overridden.
• To include a term for an interaction between factors, use the keyword BY or the asterisk
(*) to join the factors 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 inside an
interaction effect must be distinct.
• To include a term for nesting one effect within another, use the keyword WITHIN or a pair
of parentheses on the DESIGN subcommand. For example, A(B) means that A is nested
within B. The expression A(B) is equivalent to the expression A 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 on the DESIGN
subcommand.
• Covariates can be connected, but not nested, through the * operator to form another covariate
effect. Therefore, interactions among covariates such as X1*X1 and X1*X2 are valid, but not
X1(X2). Using covariate effects such as X1*X1, X1*X1*X1, X1*X2, and X1*X1*X2*X2 makes
fitting a polynomial regression model easy in GLM.
• 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.
• If more than one DESIGN subcommand is specified, only the last one is in effect.
Example
GLM Y BY A B C WITH X
/DESIGN A B(A) X*A.
• In this example, the design consists of a main effect A, a nested effect B within A, and an
interaction effect of a covariate X with a factor A.