Stratified anova vs interaction effect

Posted by parisec on Dec 05, 2014; 10:45pm
URL: http://spssx-discussion.165.s1.nabble.com/Stratified-anova-vs-interaction-effect-tp5728125.html

Hi all,

Study design: 2 groups (T1, T2), fixed factor: sex (M, F)

We hypothesized that T1 would have a stronger effect in Men versus women. I plotted means and they  clearly indicated an interaction. i stratified the analysis by sex and ran separate ANOVAs, it was clear that there was an effect in Men (p <0.02) but not in Women. I should have quit there!

But i didn't,  i ran a factorial anova that included group, sex, and the group*sex interaction term. I added the simple effects of group within sex.

  /EMMEANS=TABLES(sex*group) COMPARE (group) ADJ(LSD)

The main effect was just above significance (0.056) and interaction term was not significant, yet the simple effects term showed strong statistical significance, which i know should not be interpreted without a significant interaction.

Now i'm at a loss. The stratified analysis clearly indicates an interaction yet the formal test for interaction didn't pan out.

Is it wrong to just report the results of a stratified analysis?

Thanks for your thoughts.
Carol