Bioequivalence and Bioavailability Forum

Dear Shuanghe!

❝ […] I was stuck in boundy, and consequently, critbound.

❝ So my question is, how to calculate this "CINV" in Phoenix? I mean, I can get the value from SAS, or even from Excel, but that would mean I have to do it manually everytime.

❝ Is there any easy way to do it? or I have to import a table of the inverse chi-square distribution to match the dfd I got from linear mixed effect model?

You discovered an important point. Although both noncentral t and χ² are used internally in Phoenix, they are not accessible as a function in a custom transformation.
I discussed that at Pharsight’s Extranet, in e-mails with the developers, and filed two bugs at the support site. Since you succeeded in getting boundx you have noticed that min() and max() are not available as well (bug 11570). Instead of simply using
  (max((abs(Lower_CI)), (abs(Upper_CI))))^2
I had to workaround
  if(abs(Lower_CI)>=abs(Upper_CI), (abs(Lower_CI))^2, (abs(Upper_CI))^2)

Bug 11571 (inaccessible distributions) will not ‘make it’ in the next release 1.3 – which is already in the final testing stage and scheduled for release end of the first quarter 2012.

❝ How did you do it, if I may ask?

My workaround was essentially your last suggestion. I generated the values in R

options(digits=16)
for (dfd in 1:200) {
  Cinv <- qchisq(0.95, df=dfd)
  cat(paste(dfd, "\t", Cinv, "\n"))
}

and imported the table with column headers dfd and Cinv. In the Estimates of Intermediate Dlat I renamed Denom_DF to dfd, merged with the χ²-table (sort on dfd) and filtered for empty rows (Exclude where [Dependent] is NULL Entire Row). Another option would be a ‘Phoenix Connect’ license. Then it should be possible to obtain the value from one of the following programs: SAS, S-plus, R. I got a trial license and didn’t succeed yet – but I’m not sure whether it is really worth the efforts.

Pharsight is considering to internally code both EMA’s and FDA’s models in a future release (QC_PHX6269). Right now my workflow is rather lenghty (if you want I can send you the project file off-list). Time allowing I will prepare another whitepaper. Since the bug giving slightly different CIs from ABE and LME was fixed in v1.3 probably I will wait for the final release.