[R-sig-ME] Does lmer with default family require normal distribution of IV

[ONKELINX, Thierry]

Jerry,

Neither the response nor the covariates must be normally distributed. The assumption of normality is on the residuals of the model. Although normality is not needed for the response, if it helps to get normally distributed residuals.

Best regards,

Thierry

----------------------------------------------------------------------------
ir. Thierry Onkelinx
Instituut voor natuur- en bosonderzoek
team Biometrie & Kwaliteitszorg
Gaverstraat 4
9500 Geraardsbergen
Belgium

Research Institute for Nature and Forest
team Biometrics & Quality Assurance
Gaverstraat 4
9500 Geraardsbergen
Belgium

tel. + 32 54/436 185
Thierry.Onkelinx at inbo.be
www.inbo.be

To call in the statistician after the experiment is done may be no more than asking him to perform a post-mortem examination: he may be able to say what the experiment died of.
~ Sir Ronald Aylmer Fisher

The plural of anecdote is not data.
~ Roger Brinner

The combination of some data and an aching desire for an answer does not ensure that a reasonable answer can be extracted from a given body of data.
~ John Tukey
  

> -----Oorspronkelijk bericht-----
> Van: r-sig-mixed-models-bounces at r-project.org 
> [mailto:r-sig-mixed-models-bounces at r-project.org] Namens Jerry Zhu
> Verzonden: maandag 7 maart 2011 5:46
> Aan: r-sig-mixed-models at r-project.org
> Onderwerp: [R-sig-ME] Does lmer with default family require 
> normal distribution of IV
> 
> Hi Folks,
> I have repeated measurements for each subject. The 
> DV(response variable) is "Value", a square root 
> transformation of which makes it normally distributed. The 
> IV(predictor variable) is "Delay", which is not normally 
> distributed. Then I ran a model:
> lmer(sqrt(Value)~Delay+(Delay|Subject))
> 
> Does this model require a normally-distributed Delay?
> 
> I feel that lmer is a linear model, so it requires normal 
> distribution of both IV and DV. Am I right?
> 
> Thanks for your reply!
> 
> 	[[alternative HTML version deleted]]
> 
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