SPSS® 12.0 Command Syntax Reference

CONTRAST Subcommand
LOGLINEAR 823
CONTRAST indicates the type of contrast desired for a factor, where a factor is any categorical
dependent or independent variable. The default contrast is DEVIATION for each factor.
• The specification is CONTRAST, which is followed by a variable name in parentheses and
the contrast-type keyword.
• To specify a contrast for more than one factor, use a separate CONTRAST subcommand
for each specified factor. Only one contrast can be in effect for each factor on each
DESIGN.
• A contrast specification remains in effect for subsequent designs until explicitly overridden
by another CONTRAST subcommand.
• The design matrix used for the contrasts can be displayed by specifying keyword DESIGN
on the PRINT subcommand. However, this matrix is the basis matrix that is used to determine
contrasts; it is not the contrast matrix itself.
• CONTRAST can be used for a multinomial logit model, in which the dependent variable
has more than two categories.
• CONTRAST can be used for fitting linear logit models. The keyword BASIS is not appropriate
for such models.
• In a logit model, CONTRAST is used to transform the independent variable into a metric
variable. Again, the keyword BASIS is not appropriate.
The following contrast types are available:
DEVIATION(refcat) Deviations from the overall effect. DEVIATION is the default contrast
if the CONTRAST subcommand is not used. Refcat is the category for
which parameter estimates are not displayed (they are the negative
of the sum of the others). By default, refcat is the last category of the
variable.
DIFFERENCE Levels of a factor with the average effect of previous levels of a
factor. Also known as reverse Helmert contrasts.
HELMERT Levels of a factor with the average effect of subsequent levels of a
factor.
SIMPLE(refcat) Each level of a factor to the reference level. By default, LOGLINEAR
uses the last category of the factor variable as the reference category.
Optionally, any level can be specified as the reference category
enclosed in parentheses after the keyword SIMPLE. The sequence of
the level, not the actual value, must be specified.
REPEATED Adjacent comparisons across levels of a factor.
POLYNOMIAL(metric) Orthogonal polynomial contrasts. The default is equal spacing.
Optionally, the coefficients of the linear polynomial can be specified
in parentheses, indicating the spacing between levels of the treatment
measured by the given factor.