[R-sig-ME] Justification to exclude random effect

[Baldwin, Jim -FS]

I'm not seeing enough information to make such a decision - although in any event, I don't see that the slight additional complexity of a single random effect would warrant the need to re-run the analysis without it.  Plus, if the random effect was part of the experimental layout, then (other than maybe having too few levels to be able to estimate adequately it as a random effect) it ought to be in the model.

Does this deal with count data or something more continuous?  Are the residuals well behaved?

Jim


-----Original Message-----
From: R-sig-mixed-models [mailto:r-sig-mixed-models-bounces at r-project.org] On Behalf Of Reuben Smit
Sent: Monday, May 09, 2016 4:16 PM
To: r-sig-mixed-models at r-project.org
Subject: [R-sig-ME] Justification to exclude random effect

Hello,

The results of my mixed model show the single random effect variance and standard deviation equal to zero. A statistician reviewed my results and suggested the random effect is not explaining any additional variance apart from the fixed effects. I'm asking the list to support or refute this claim based on the aforementioned variance and standard deviation estimate. If indeed the random effect is not contributing to the model, is it justified to exclude the random effect and may I use a more simple generalized linear model with fixed effects only?

Also, the random effect is the effect of Site from a random nested study design. My conjecture is that a longitudinal/spatial fixed effect is accounting for relatedness between sample points located in the same Site (block).

Thanks in advance,
Reuben

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