SPSS® 12.0 Command Syntax Reference

682 GLM: Repeated Measures
POLYNOMIAL Polynomial contrasts. This is the default for within-subjects factors. The
first degree of freedom contains the linear effect across the levels of the
factor, the second contains the quadratic effect, and so on. In a balanced
design, polynomial contrasts are orthogonal. By default, the levels are
assumed to be equally spaced; you can specify unequal spacing by entering
a metric consisting of one integer for each level of the factor in parentheses
after the keyword POLYNOMIAL. (All metrics specified cannot be equal; thus
(1, 1, ..., 1) is not valid.) For example,
/WSFACTOR=D 3 POLYNOMIAL(1,2,4).
Suppose that factor D has three levels. The specified contrast indicates that
the three levels of D are actually in the proportion 1:2:4. The default metric
is always (1,2,...,k), where k levels 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, in each instance, the difference between the second
and third numbers is twice the difference between the first and second.
DIFFERENCE Difference or reverse Helmert contrasts. Each level of the factor except the
first is compared to the mean of the previous levels. In a balanced design,
difference contrasts are orthogonal.
HELMERT Helmert contrasts. Each level of the factor except the last is compared to
the mean of subsequent levels. In a balanced design, Helmert contrasts are
orthogonal.
SIMPLE Each level of the factor except the last is compared to the last level. To use
a category other than the last as the omitted reference category, specify its
number in parentheses following keyword SIMPLE. For example,
/WSFACTOR=B 3 SIMPLE (1).
Simple contrasts are not orthogonal.
REPEATED Comparison of adjacent levels. Each level of the factor except the first is
compared to the previous level. Repeated contrasts are not orthogonal.
SPECIAL A user-defined contrast. Values specified after this keyword are stored in a
matrix in column major order. For example, if factor A has three levels, then
WSFACTOR(A)= SPECIAL(1 1 1 1 -1 0 0 1 -1) produces the following contrast
matrix:
1 1 0
1 –1 1
1 0 –1
Example
GLM X1Y1 X1Y2 X2Y1 X2Y2 X3Y1 X3Y2 BY TREATMNT GROUP
/WSFACTOR=X 3 Y 2
/DESIGN.
• The GLM variable list names six dependent variables and two between-subjects factors,
TREATMNT and GROUP.