The documentation on Proc Mixed is very thorough when it comes to describing methods for calculating denominator degrees of freedom (DDFM=CONTAIN, or BETWITHIN, or RESIDUAL, or SATTERTH, or KENWARDROGER), but it doesn't give any guidance on which method to use and when. Over the years I've used Proc Mixed in the pharmaceutical industry, this is all I've been able to gather on this topic:
- At a previous job, the conventional wisdom was DDFM=KENWARDOGER is preferable, but there was nothing concrete to support this statement.
- The FDA's guidance on individual bioequivalence (2001) provides sample Proc Mixed code which uses DDFM=SATTERTH. Is there anything more current?
- At one time, for _nonlinear_ mixed effects models, Doug Bates eschewed computing the denominator degrees of freedom altogether, and instead relied on bootstrapping for inference.
Any insights that anyone might have on this issue would be very welcome. Thanks!
ZardozJr