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 :) >

----- -- Bruce Weaver bweaver@lakeheadu.ca http://sites.google.com/a/lakeheadu.ca/bweaver/

"When all else fails, RTFM."

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