Pooled Effects: Plus Sign (MANOVA: Univariate command)

To pool different effects for the purpose of significance testing, join the effects with a plus sign (+). A single test is made for the combined effect of the pooled terms.

• The keyword BY is evaluated before effects are pooled together.
• Parentheses are not allowed for changing the order of evaluation. For example, it is illegal to specify (A + B) BY C. You must specify /DESIGN=A BY C + B BY C.

Example

MANOVA Y BY A(1,3) B(1,4) WITH X
 /ANALYSIS=Y
 /DESIGN=A, B, A BY B, A BY X + B BY X + A BY B BY X. 

• This example shows how to test homogeneity of regressions in a two-way analysis of variance.
• The + signs are used to produce a pooled test of all interactions involving the covariate X. If this test is significant, the assumption of homogeneity of variance is questionable.