Downtown with Sky

Answers to Applied PhD Comprehensive Question #2

I’ve been busy with teaching, so I’m only now getting around to posting the answers to the second applied statistic comprehensive exam question that I posted (here).

Originally, I’d thought that posting the answer would be simply a matter of extracting the answer I’d already written before.  But looking it over before posting, I noticed that I’d made an additional unintentional error in the analysis that the question asks you to critique! Of course, one could say that the more errors the better, but I did need to update my answer to reflect this.

The error is that in the first analysis presented, I had intended to include interaction terms between treatment and covariates such as sex in the regression shown.  Due to some sort of momentary brain failure, I instead just put these covariates in by themselves.  When writing up my answer later (which students who wrote the exam got), my mind was set on the idea that I’d put in interaction terms, so this error wasn’t reflected in that answer.  I don’t think this had any significant effect on the marking, fortunately, since the comments on the later analyses aren’t really affected.  It does show how easy it is to keep seeing what you expect to see.

Here’s the PDF file with the answers.  The questions are included as well, so no need to refer back to them.