Journal of Statistical Software (Dec 2017)

lmerTest Package: Tests in Linear Mixed Effects Models

  • Alexandra Kuznetsova,
  • Per B. Brockhoff,
  • Rune H. B. Christensen

DOI
https://doi.org/10.18637/jss.v082.i13
Journal volume & issue
Vol. 82, no. 1
pp. 1 – 26

Abstract

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One of the frequent questions by users of the mixed model function lmer of the lme4 package has been: How can I get p values for the F and t tests for objects returned by lmer? The lmerTest package extends the 'lmerMod' class of the lme4 package, by overloading the anova and summary functions by providing p values for tests for fixed effects. We have implemented the Satterthwaite's method for approximating degrees of freedom for the t and F tests. We have also implemented the construction of Type I - III ANOVA tables. Furthermore, one may also obtain the summary as well as the anova table using the Kenward-Roger approximation for denominator degrees of freedom (based on the KRmodcomp function from the pbkrtest package). Some other convenient mixed model analysis tools such as a step method, that performs backward elimination of nonsignificant effects - both random and fixed, calculation of population means and multiple comparison tests together with plot facilities are provided by the package as well.

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