Dear Rohan, Bert Gunter has already made several general useful suggestions. In addition, why did you make the variable on the left-hand side of the model a factor? Shouldn't it be a numeric variable? I hope this helps, John -- John Fox, Professor Emeritus McMaster University Hamilton, Ontarion, Canada web: https://socialsciences.mcmaster.ca/jfox/ On 4/7/2022 6:30 AM, Rohan Richard via R-help wrote:> Dear Help Desk, > > I am trying to perform a non-linear regression (Sigmoid curves) using the R package nlme. My field trial is a randomised complete block design (RCBD) with 3 blocks and I would like to assess the block effect in the model. Do you know how I can incorporate the block term in nlme function? > > So far I tried the following code and it did not work and I an error error message: > > # code > minitab$NDVI<-as.factor(minitab$NDVI) > modnlme1 <- nlme(NDVI ~ a + d / (1 + exp(-b * (DegreeDay - m)) ), data = minitab, > random =a + d + b + m~ 1|Block, > fixed = list(a ~ Lines1, d~Lines1,b ~ Lines1, m ~ Lines1), > weights = varPower(), > start=c(b=0.5,c=3,d=0.4, e=700), control = list(msMaxIter = 200)) > > #Error message > Error in `contrasts<-`(`*tmp*`, value = contr.funs[1 + isOF[nn]]) : > contrasts can be applied only to factors with 2 or more levels > > Could you please kindly help me? > > Thank you in advance, > > Best wishes, > > Rohan > > Sent from Mail<https://go.microsoft.com/fwlink/?LinkId=550986> for Windows > > > Rothamsted Research is a company limited by guarantee, registered in England at Harpenden, Hertfordshire, AL5 2JQ under the registration number 2393175 and a not for profit charity number 802038. > > [[alternative HTML version deleted]] > > ______________________________________________ > R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see > 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.