The rule thumb for eta-squared effect size is .01 for small, .06 for medium and .14 for large according to Cohen (1988)
The calculation of Eta Squared for Mixed design based on SPSS output-- which is sort of different from the general ANOVA models- can be found here.
Essentially:
eta squared for within=(ss within effect)/(ss within total)
eta squared for between=(ss between effect)/(ss between total)
One thing worth mentioning is that-- say you have one between variable called group, you will see on your between-factor output 3 sources: Intercept, Group, Error. The SS total for between factor= SS Group+SS Error. Let go of the intercept.
The calculation of Eta Squared for Mixed design based on SPSS output-- which is sort of different from the general ANOVA models- can be found here.
Essentially:
eta squared for within=(ss within effect)/(ss within total)
eta squared for between=(ss between effect)/(ss between total)
One thing worth mentioning is that-- say you have one between variable called group, you will see on your between-factor output 3 sources: Intercept, Group, Error. The SS total for between factor= SS Group+SS Error. Let go of the intercept.
