Re: Questions about ANOVAs and Sphericity

Posted by Bruce Weaver on Apr 12, 2011; 7:11pm
URL: http://spssx-discussion.165.s1.nabble.com/Questions-about-ANOVAs-and-Sphericity-tp4297706p4298951.html

Here is a nice note on sphericity that you may find helpful.

   http://psychologicalstatistics.blogspot.com/2006/05/what-is-all-this-stuff-about.html

HTH.

rohanp16 wrote

Hello everyone !! :)

I had a few questions about ANOVAs and sphericity. I am conducting a 2 way ANOVA with one factor (A) having two levels and the other factor (B) having 21 levels.

Q1) In the 'Within Subjects effects' Table I see there is a main effect of factor B. One should then go to 'planned comparisons' to see where the effect lies right ? However SPSS throws out a 'multivariate tests' output just below the 'planned comparisons' table. What does this table mean ? Below the table it says

"Each F tests the multivariate effect of Factor B. These tests are based on the linearly independent pairwise comparisons among the estimated marginal means"

What does this table mean ? I'm 90% sure there is no need to look at this table, but REALLY want to know what it means.

Q2) I have a significant interaction effect (A*B) and I used the following syntax to see where the difference lied,

  /EMMEANS=TABLES(A*B) COMPARE(B) ADJ(BONFERRONI)
  /EMMEANS=TABLES(B*A) COMPARE(A) ADJ(BONFERRONI)

The output that SPSS throws out, I should first look at the 'Multivariate tests' table and only if that is significant do I see which direction the differences lie in the 'Planned comparisons' table right ?

Q3) While conducting the Mauchly's Test of Sphericity, I realize one requires more than 2 levels of a variable for sphericity to be an issue. So for factor A I get a value of 1 for Mauchly's W which means sphericity is not an issue (and a . in the 'significance' column). However for my other factor, I get a 0.000 and no significance value (i.e - once again there is . in the significance column). Does that mean sphericity is an issue or is not an issue ? If it was an issue, why didn't it just spit out some value <0.05 in the significance column?

Thanks a lot, take care :)