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
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