Addendum to my previous answer : In that special case, the limited range of the asin(sqrt()) transformation, which is a shortcoming, turns out to be useful. The fixed-effect doefficients seem semi-reasonable (except for stageB) :
> (sin(coef(lm(asin(sqrt(MH.Index))~0+stage, data=similarity))))^2 stageA stageB stageC stageD 0.6164870 0.3389430 0.5083574 0.5672021 The random effects being nested in the fixed efect, one can't afford to be lazy in the parametrization of the corresponding random effect : > summary(lmer(asin(sqrt(MH.Index))~stage+(stage|site), data=similarity)) Linear mixed model fit by REML Formula: asin(sqrt(MH.Index)) ~ stage + (stage | site) Data: similarity AIC BIC logLik deviance REMLdev 155.3 199 -62.65 111.8 125.3 Random effects: Groups Name Variance Std.Dev. Corr site (Intercept) 0.043579 0.20876 stageB 0.033423 0.18282 -0.999 stageC 0.043580 0.20876 -1.000 0.999 stageD 0.043575 0.20875 -1.000 0.999 1.000 Residual 0.128403 0.35833 Number of obs: 136, groups: site, 39 Fixed effects: Estimate Std. Error t value (Intercept) 0.93036 0.08431 11.035 stageB -0.30879 0.10079 -3.064 stageC -0.13660 0.09981 -1.369 stageD -0.07755 0.14620 -0.530 Correlation of Fixed Effects: (Intr) stageB stageC stageB -0.836 stageC -0.845 0.707 stageD -0.577 0.482 0.487 > v<-fixef(lmer(asin(sqrt(MH.Index))~stage+(stage|site), data=similarity)) > v[2:4]<-v[1]+v[2:4] > names(v)[1]<-"stageA" > (sin(v))^2 stageA stageB stageC stageD 0.6429384 0.3390903 0.5083574 0.5672021 But again, we're exploiting a shortcoming of the asin(sqrt()) transformation. HTH, Emmanuel Charpentier Le vendredi 16 avril 2010 à 00:15 -0800, Kay Cichini a écrit : > thanks thierry, > > i considered this transformations already, but variance is not stabilized > and/or normality is neither achieved. > i guess i'll have to look out for non-parametrics? > > best regards, > kay ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.