[R-sig-ME] degree of freedom is non-integer from lmerTest

[Yuqi Liu]

Dear R-experts,

  I am using lmerTest to do mixed model analysis on one of my experiments. There are two factors, each with 2 levels, resulting in 4 experiment conditions.  It was repeated measures design, and each experiment condition was conducted once for each individual. The model is thus very simple, with each factor as a fixed effect and subjects as a random effect: model <- lmerTest (DV~IV1*IV2+(1|subject),data).

 When I looked at the result using summary(model), the Dfs are non-integers, is it because we had to exclude some of the trials, so that some participants had missing data? In general, I am wondering how t-tests are performed in lmerTest, and how degree of freedom was calculated.

Thank you for your help!
Yuqi

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