RE: Decrease in OFV with a fixed effect

From: "Serge Guzy" GUZY@xoma.com Subject: RE: [NMusers] Decrease in OFV with a fixed effect Date: Tue, August 24, 2004 12:18 pm You are right about V1 not being fixed and therefore you speak about two different models. The issue was that without covariate, V1 does not have random effect associated with it (eta is very very small). This seems to suggest that V1 is the same across all individual and therefore we should not expect a correlation between weight and V1. However, confounding factors that flip flop random effects with covariate effect is not uncommon. When there are no covariate, most of the interindividual variability can be found in some of the parameters and not in V1(may be by chance only). When assuming a correlation (without random effect), a flip flop between 2 different effects occur. I am pretty sure that at least one random effect from all other parameters (except V1) is different in the covariate model and the one without covariate. Serge Guzy _______________________________________________________