getDDFM function

Degrees of Freedom for Testing Linear Contrasts of Fixed Effects and Least Square Means

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.

getDDFM(
  obj,
  L,
  ddfm = c("contain", "residual", "satterthwaite"),
  tol = 1e-12,
  method.grad = "simple",
  opt = TRUE,
  items = NULL
)

Arguments

• obj: (VCA) object
• L: (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

Returns

(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'.

See Also

test.fixef

Author(s)

Andre Schuetzenmeister andre.schuetzenmeister@roche.com