Ulrich Halekoh, S<c3><b8>ren H<c3><b8>jsgaard (2014).,
A Kenward-Roger Approximation and Parametric Bootstrap Methods for Tests in Linear Mixed Models - The R Package pbkrtest.,
Journal of Statistical Software, 58(10), 1-30., http://www.jstatsoft.org/v59/i09/
See Also
KRmodcompPBmodcompvcovAdj
Examples
data(beets, package='pbkrtest')
lg <- lmer(sugpct ~ block + sow + harvest + (1|block:harvest),
data=beets, REML=FALSE)
sm <- update(lg, .~. - harvest)
xx<-KRmodcomp(lg, sm)
getKR(xx, "ddf") # get denominator degrees of freedom.