[R-sig-ME] FW: linear mixed model for non-normal negative and continous data

[Simon Blomberg]

You could try using the Yeo-Johnson transformation in the car package.

Cheers,

Simon.

On 28/04/14 21:31, Caroline Lustenberger wrote:
> Dear all
>   
> I try to fit a linear mixed model to my data. In short, my dependent variable reflects changes of the bone level (Knmn, in mm), thus this variable is continous and provides negative values. I have two different groups (factor Group) that were measured 3 times each (thus repeated measures, factor Timepoint). I used the following model:
>   
> mod_Knmn<-lmer(Knmn~Group*Timepoint+(1|VPnr),data=data)
>   
> When performing a qq-plot my residuals are clearly deviant from the norm (long-tailed). Due to negative values I cannot perform classical transformation methods (e.g. log transformation). How could I proccede with this data. Is there a possibility to use a generalized linear model?
>   
> Thanks and all the best
> Caroline
>
>   		 	   		
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>
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-- 
Simon Blomberg, BSc (Hons), PhD, MAppStat, AStat.
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