Message-ID: <1727864569.64791379940746607.JavaMail.www@wwinf7130>
Date: 2013-09-23T12:52:26Z
From: v_coudrain at voila.fr
Subject: Variance structure in mixed models
Dear all,
I modelled my data with a quasi-poisson error distribution using glm: glm(response~variable1 + factor1 , family=quasipoisson). Looking at the plot of residuals vs
factor 1, I noticed a large heterogeneity in residual variance between the different levels of my factor. With a linear regression, there is the option of using a
different variance structure for different levels using the option "varIdent" (funtion gls, package nlme). I could not find any equivalent for mixed models. Could
anybody explain me why and if there is another possibilty to account for variance heterogeneity?
Thank you very much
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