Thank you, I have a question nobody around me can answer so I'm à bit stuck : I did a mancova in spss (with a 3-group indépendant variable, 6 dépendant variables and two covariates), asking for estimated marginal means as well as saving the predicted (unstandardized) scores for all my individuals in the data file. From what I understand, these scores are calculated based on the marginal means (taking into account the covariates). And indeed, they are quite different from the initial scores. But what I don't understand is that, when I then do a simple manova using these new scores (and no covariates, just a manova), not only the results (F) are not the same as the mancova's corrected model, but the marginal means are also different. Would you know where I am mistaken please? Sorry for the length of this question (and probably my English since I'm French !)
Levenes test indicates a problem with heteroscedasticity (or lack of constant residual variances) when significant. It is not used to test for heterogeneity of regression slopes. Heterogeneity of regression slopes is tested by including a group x covariate interaction term in your model. If that term is significant, it is an indication that the linear relationship between covariate and dv varies across groups.
