[R-sig-ME] PIECEWISE MIXED-EFFECT MODELING

[Dimitris Rizopoulos]

the '*' operator has a special meaning inside a formula statement -- 
have a look at function I() if you'd like to use '*' in the standard 
way. Try the following (untested):

CD40 <- lme(cd4 ~ I(rt*(rt<25)) + I(rt*(rt>=25)), data = frame1,
   random = ~ rt | id, na.action = na.omit)


I hope it helps.

Best,
Dimitris


On 3/6/2011 12:33 AM, Federico Bonofiglio wrote:
> Hi Folks,
> I'd really really appreciate if anyone could give me a quick advise for this
> one:
>
> I want to fit a piecewise mixed effect model, but it seems I'm not getting
> around it
>
>> CD40<-lme(cd4~rt*(rt<25)+rt*(rt>=25),data=frame1,
> +   random= ~rt|id, na.action=na.omit)
> *
> Errore in MEEM(object, conLin, control$niterEM) :
>    Singularity in backsolve at level 0, block 1
> *
> Would anyone have a clue of the matter ?
>
> Huge thanks.
> Federico Bonofiglio

-- 
Dimitris Rizopoulos
Assistant Professor
Department of Biostatistics
Erasmus University Medical Center

Address: PO Box 2040, 3000 CA Rotterdam, the Netherlands
Tel: +31/(0)10/7043478
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