Bioequivalence and Bioavailability Forum

Hi ElMaestro,

❝ There is still no option to do the equivalent of DDFM=Satt in R for any of the available packages, as far as I know.

Yep. Some background here, especially:

• Because the primary authors of lme4 are not convinced of the utility of the general approach of testing with reference to an approximate null distribution, and because of the overhead of anyone else digging into the code to enable the relevant functionality (as a patch or an add-on), this situation is unlikely to change in the future.

No Satterthwaite approximation; at least the Kenward & Roger approximation^{1 (why not 2?)} is available in the package pbkrtest (reference). But this is not what FDA wants…

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References:
1. Kenward MG, Roger JH. Small Sample Inference for Fixed Effects from Restricted Maximum Likelihood. Biometrics. 1997;53(3):983–97.
   
2. Kenward MG, Roger JH. An Improved Approximation to the Precision of Fixed Effects from Restricted Maximum Likelihood. Comp Stat Data Anal. 2009;53(7):2583–95.