[UPDATE: I have been unable to find any information on Andrew Carson, so I wonder if this is a real person or a pseudonym. I also hope that at one point the data will be released to interested parties, so we can check for accuracy; for all I know this is a hoax.--ES]
I haven't had a chance to look at his approach, so I will just report his bottom line:
If you are applying to graduate schools in philosophy and are trying to decide which schools you want to apply to or attend, and if you are concerned about your placement prospects after graduation, you need to consider (1) how a school ranks in your chosen specialty and (2) how well that school places students overall. You cannot just rely on overall faculty rankings, for these bear no relationship to how well a school places, although many will find these rankings important for other reasons. What does appear to matter as far as placement is concerned is the school's ranking in your area of specialty. If it ranks well, then you have a much higher chance of getting a tenure track or permanent position in academic philosophy. And some schools just appear to have better placement rankings than others. For example, both Northwestern University and University of Massachusetts, Amherst are not ranked above a 3 in any category (except Continental philosophy and Social and Political Philosophy, respectively), but they have some of the best placement records.
Why is that? I wish I knew. That is a question worthy of further exploration...[Emphasis in original--ES.]