[R] Mac/PC differences in lmer results

[Nicolas Schuck]

Dear fellow R coders, 

I am observing differences in results obtained using glmer when using a Mac or Linux computer versus a PC. Specifically, I am talking about a relatively complex glmer model with a nested random effects structure. The model is set up in the following way: 
gcctrl = glmerControl(optimizer=c('nloptwrap'), optCtrl = list(maxfun = 500000), calc.derivs = FALSE)

glmer_pre_instr1 = glmer(
      formula = cbind(FREQ, NSAMP-FREQ) ~ FDIST_minz + poly(RFREQ,2) + ROI + (1 + FDIST_minz + RFREQ + ROI|ID/COL), 
      data = cdf_pre_instr, 
      family = binomial, 
      control = gcctrl)

Code and data of an example for which I find reproducible, non-negligible differences between Mac/Win can be found here: https://gitlab.com/nschuck/glmer_sandbox/tree/master <https://gitlab.com/nschuck/glmer_sandbox/tree/master>
The differences between the fitted models seem to be most pronounced regarding the estimated correlation structure of the random effects terms. Mac and Linux yield very similar results, but Windows deviates quite a bit in some cases. This has a large impact on p values obtained when performing model comparisons. I have tried this on Mac OS 10.14, Windows 10 and Ubuntu and Debian. All systems I have tried are using lme 1.1.21 and R 3.5+. 

Does anyone have an idea what the underlying cause might be? 

Thanks, 
Nico 
 



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