SPSS® 12.0 Command Syntax Reference

1614 UNIANOVA
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 (which is not necessarily the same as its value) in parentheses
following the keyword SIMPLE. For example,
UNIANOVA Y BY B
/CONTRAST(B)=SIMPLE(1).
Suppose that factor B has three levels with values 2, 4, and 6. The specified
contrast compares the other levels to the first level of B, in which B has the
value 2. 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
CONTRAST(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
Orthogonal contrasts are particularly useful. In a balanced design, contrasts are orthogonal
if the sum of the coefficients in each contrast row is 0 and if, for any pair of contrast
rows, the products of corresponding coefficients sum to 0. DIFFERENCE, HELMERT, and
POLYNOMIAL contrasts always meet these criteria in balanced designs.
Example
UNIANOVA DEP BY FAC
/CONTRAST(FAC)=DIFFERENCE
/DESIGN.
• Suppose that the factor FAC has five categories and therefore four degrees of freedom.
• CONTRAST requests DIFFERENCE contrasts, which compare each level (except the first)
with the mean of the previous levels.