according to collegehelp, one can calculate a college's PA score quite accurately from knowing things like a proxy for overall faculty research quality, financial status of the college, and some measures of student preparation and graduation rates.
http://talk.collegeconfidential.com/...eer+assessment
For universities, the formula explained 94% of the variance in PA scores. For LAC's a similar formula, that omitted faculty research, explained 84%
So these appear to be what the academics are really looking at when they generate the PA scores.