Hi, I use the package "nlme" to fit linear regression on data that has 27 groups (subjects). The following is my scripts. lw <- groupedData( y ~ x | group, data = read.table("lw.d",header=T)) lw1 <- lme(y~x,data=lw,random= ~x | group) Everaything o.k. up to this point. However, the next one, lw2 <- lme(y~x+sex,data=lw,random= ~x | group), where sex is classification factor with M=male and F=female, gives the following message: Error in MEEM(object, conLin, control$niterEM) : Singularity in backsolve at level 0, block 1 Is any fix to this problem? Cheers! Han -.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.- r-help mailing list -- Read ci.tuwien.ac.at/~hornik/R/R-FAQ.html Send "info", "help", or "[un]subscribe" (in the "body", not the subject !) To: r-help-request at stat.math.ethz.ch _._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._