getDDFM: Degrees of Freedom for Testing Linear Contrast of Fixed Effects and Least Square Means.
Description
There are three methods implemented, which are all available in SAS PROC MIXED, namely
"contain", "residual", and "satterthwaite" approximations. See the documentation of SAS
PROC MIXED for details on this topic.
(numeric) vector specifying the linear combination of the fixed effect or
LS Means
ddfm
(character) string specifying the method used for computing the denominator
degrees of freedom for tests of fixed effects or LS Means. Available methods are
"contain", "residual", and "satterthwaite".
tol
(numeric) value specifying the numeric tolerance for testing equality to zero
method.grad
(character) string specifying the method to be used for approximating the gradient
of the variance-covariance matrix of fixed effects at the estimated covariance parameter
estimates (see function 'grad' (numDeriv) for details)
opt
(logical) TRUE = tries to optimize computation time by avoiding unnecessary computations
for balanced datasets (see test.fixef).
items
(list) of pre-computed values
Value
(numeric) vector with the specified type of degrees of freedom
Details
The implementation of the Satterthwaite approximation was inspired by the code of function
'calcSatterth' of R-package 'lmerTest'.