Notice: On April 23, 2014, Statalist moved from an email list to a forum, based at statalist.org.
From | Ana Beatriz FS <nutrianabeatriz@gmail.com> |
To | statalist@hsphsun2.harvard.edu |
Subject | Re: st: Mixed effects model for asymmetric data |
Date | Wed, 26 Sep 2012 15:15:45 -0300 |
Thanks, JVVerkuilen, Unfortunately my variable is not a count one, I work with levels of hormones. Following your suggestion, I assessed the quality of the model by the residuals and it's really really bad. With respect to the transformations, they produce quite different distributions. I haven't find one that would fit all my points in time, even if not perfectly. I do think I have a problem here! Best regards, Ana Beatriz 2012/9/26 JVerkuilen (Gmail) <jvverkuilen@gmail.com>: > On Wed, Sep 26, 2012 at 1:13 PM, Ana Beatriz FS > <nutrianabeatriz@gmail.com> wrote: >> Dear Statalisters, >> >> I was performing multilevel mixed-effects linear regression but I >> realized my data is not normally distributed. Is there an equivalent >> model for asymmetric data in stata? >> >> I've tried to transform my data but I could not accomplish because my >> data require different transformations in each point of follow-up. My >> sample is composed by pregnant women in the three trimesters of >> pregnancy, but values of my dependent variable in first trimester >> require log transformation for normalization, in the second, sqrt >> transformation and so on. > > What are the measures? For instance, if they are counts, you might be > better off with -xtmepoisson-, which assumes that you have multilevel > Poisson distributed data. If the transformations are all fairly close, > you can probably get away with choosing one, so if the right answer is > sqrt and you log instead it won't be *that* far off. Also keep in mind > that the marginal distribution before conditioning on regressors can > be rather far from normal, so it's not really clear you need to do any > transformation. What do the residuals look like? > > > -- > JVVerkuilen, PhD > jvverkuilen@gmail.com > > "Out beyond ideas of wrong-doing and right-doing there is a field. > I'll meet you there. When the soul lies down in that grass the world > is too full to talk about." ---Rumi > * > * For searches and help try: > * http://www.stata.com/help.cgi?search > * http://www.stata.com/support/statalist/faq > * http://www.ats.ucla.edu/stat/stata/ * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/