lmerTest Package: Tests in Linear Mixed Effects Models

• Published in: Journal of statistical software Vol. 82; no. 13; pp. 1 - 26
• Main Authors: Kuznetsova, Alexandra, Brockhoff, Per B., Christensen, Rune H. B.
• Format: Journal Article
• Language: English
• Published: Foundation for Open Access Statistics 01.12.2017
• Subjects: denominator degree of freedom, Satterthwaite's approximation, ANOVA, R, linear mixed effects models, lme4
• ISSN: 1548-7660; 1548-7660
• DOI: 10.18637/jss.v082.i13

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.