SPSS® 12.0 Command Syntax Reference

LOGISTIC REGRESSION 807
DEVIATION(refcat) Deviations from the overall effect. The effect for each category of the
independent variable except one is compared to the overall effect.
Refcat is the category for which parameter estimates are not displayed
(they must be calculated from the others). By default, refcat is the last
category. To omit a category other than the last, specify the sequence
number of the omitted category (which is not necessarily the same as
its value) in parentheses after the keyword DEVIATION.
SIMPLE(refcat) Each category of the independent variable except the last is compared
to the last category. To use a category other than the last as the omitted
reference category, specify its sequence number (which is not necessarily
the same as its value) in parentheses following the keyword
SIMPLE.
DIFFERENCE Difference or reverse Helmert contrasts. The effects for each category
of the independent variable except the first are compared to the mean
effects of the previous categories.
HELMERT Helmert contrasts. The effects for each category of the independent
variable except the last are compared to the mean effects of subsequent
categories.
POLYNOMIAL(metric) Polynomial contrasts. The first degree of freedom contains the linear
effect across the categories of the independent variable, the second
contains the quadratic effect, and so on. By default, the categories are
assumed to be equally spaced; unequal spacing can be specified by
entering a metric consisting of one integer for each category of the
independent variable in parentheses after the keyword POLYNOMIAL.
For example, CONTRAST(STIMULUS)=POLYNOMIAL(1,2,4)
indicates that the three levels of STIMULUS are actually in the proportion
1:2:4. The default metric is always (1,2, ..., k), where k categories
are involved. Only the relative differences between the terms of the
metric matter: (1,2,4) is the same metric as (2,3,5) or (20,30,50)
because the difference between the second and third numbers is twice
the difference between the first and second in each instance.
REPEATED Comparison of adjacent categories. Each category of the independent
variable except the first is compared to the previous category.
SPECIAL(matrix) A user-defined contrast. After this keyword, a matrix is entered in
parentheses with k – 1 rows and k columns (where k is the number of
categories of the independent variable). The rows of the contrast
matrix contain the special contrasts indicating the desired comparisons
between categories. If the special contrasts are linear combinations
of each other, LOGISTIC REGRESSION reports the linear
dependency and stops processing. If k rows are entered, the first row
is discarded and only the last k –
1 rows are used as the contrast
matrix in the analysis.