Search code examples
rlme4gamma

error message when performing Gamma glmer in R- PIRLS step-halvings failed to reduce deviance in pwrssUpdate

I am trying to perform a glmer in R using the Gamma error family. I get the error message: "Error: (maxstephalfit) PIRLS step-halvings failed to reduce deviance in pwrssUpdate"

my response variable is flower mass. My fixed effects are base mass, F1 treatment, and fertilisation method. My random effects are line and maternal ID nested within line.

When I perform the same analysis using an integer as the response (ie. flower number) This error does not occur.

Here is a sample of my data:

LINE MATERNAL_ID  F1TREAT  SO   FLWR_MASS  BASE_MASS
17   81           stress   s    2.7514     9.488
5    41           control  o    0.3042     1.809
37   89           control  o    2.3749     6.694
5    41           stress   s    3.6140     9.729
9    5            control  s    0.5020     7.929
13   7            stress   s    0.4914     0.969
35   88           stress   s    0.4418     1.840
1    57           control  o    2.1531     6.673
13   7            stress   s    3.0191     7.131

Here is the code I am using:

library(lme4)
m <- glmer(data=mydata,
           FLWR_MASS~BASE_MASS*F1TREAT*SO+(1 |LINE/MATERNAL_ID),family=Gamma)

(I am using r 3.0.3 for windows)

Solution

  • @HongOoi answered this question in the comments, but I will repeat it here for anyone else having this issue. He suggested changing

    family=Gamma

    to

    family=Gamma(link=log)