PIECEWISE MIXED-EFFECT MODELING
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 Fax: +31/(0)10/7043014 Web: http://www.erasmusmc.nl/biostatistiek/