# lmerTest Package: Tests in Linear Mixed Effects Models

“lmerTest Package: Tests in Linear Mixed Effects Models” (2017), by Alexandra Kuznetsova et al. Mathematics research paper. Original abstract below, unchanged. A free PDF is available.

- Authors: Alexandra Kuznetsova, Per B. Brockhoff, Rune Haubo Bojesen Christensen
- Published: January 1, 2017
- Field: Mathematics
- DOI: https://doi.org/10.18637/jss.v082.i13
- Free PDF: https://www.jstatsoft.org/index.php/jss/article/view/v082i13/v82i13.pdf

## Abstract

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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