get_ddf_Lb function

Adjusted denominator degrees of freedom for linear estimate for linear mixed model.

Get adjusted denominator degrees freedom for testing Lb=0 in a linear mixed model where L is a restriction matrix.

get_Lb_ddf(object, L)

## S3 method for class 'lmerMod'
get_Lb_ddf(object, L)

get_ddf_Lb(object, Lcoef)

## S3 method for class 'lmerMod'
get_ddf_Lb(object, Lcoef)

Lb_ddf(L, V0, Vadj)

ddf_Lb(VVa, Lcoef, VV0 = VVa)

Arguments

• object: A linear mixed model object.
• L: A vector with the same length as fixef(object) or a matrix with the same number of columns as the length of fixef(object)
• Lcoef: Linear contrast matrix
• V0, Vadj: The unadjusted and the adjusted covariance matrices for the fixed effects parameters. The unadjusted covariance matrix is obtained with vcov() and adjusted with vcovAdj().
• VVa: Adjusted covariance matrix
• VV0: Unadjusted covariance matrix

Returns

Adjusted degrees of freedom (adjustment made by a Kenward-Roger approximation).

Examples

(fmLarge <- lmer(Reaction ~ Days + (Days|Subject), sleepstudy))
## removing Days
(fmSmall <- lmer(Reaction ~ 1 + (Days|Subject), sleepstudy))
anova(fmLarge, fmSmall)

KRmodcomp(fmLarge, fmSmall)  ## 17 denominator df's
get_Lb_ddf(fmLarge, c(0, 1)) ## 17 denominator df's

# Notice: The restriction matrix L corresponding to the test above
# can be found with
L <- model2restriction_matrix(fmLarge, fmSmall)
L

References

Ulrich Halekoh, Søren Højsgaard (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., https://www.jstatsoft.org/v59/i09/

See Also

KRmodcomp, vcovAdj, model2restriction_matrix, restriction_matrix2model

Author(s)

Søren Højsgaard, sorenh@math.aau.dk