A proxy is an indirect measure. Sometimes a measure can have two functions; for example, you can measure X in order to (or accidentally) indirectly track Y (where X is something interesting in its own right). Something is a decent proxy (X) if it will co-vary with Y. Unless one has very well confirmed background theory, it’s very hard to tell if a proxy is reliable (accurate, etc.). Absent such background theory, one way to tell if your proxy (X) is reliable, is to measure the target system Y directly, say, periodically (and – let’s stipulate – with greater difficulty and expense). Of course, if one can measure Y directly and reliably without a proxy measure, then the proxy measure becomes dispensable unless X holds out independent interest. Ideally, direct and indirect measures work in tandem so that lacunae in each become visible and modelers and end-users of the models get a clearer sense of social reality. Of course, among intentional systems with feedback loops the measures themselves become part of the causal nexus and may well play some role in shaping the evolution of the system. So, that a measure X can be a proxy for Y, and play some role in the future development of social ecology (Z).
With that jargon, let’s turn to professional philosophy (recall this post, in particular).
The Philosophical Gourmet rankings (hereafter PGR) are said to be "primarily measures of faculty quality and reputation" of selected institutions and indirectly measures of employability. The PGR aggregates expert judgments by way of a survey of selected, expert faculty. In addition to measuring quality, one of the main purposes is to guide student choices in graduate education. Several tabs in the report are directly related to and informative about graduate education, choosing graduate departments, as well as job placement (and "employment"). They are, thus, also a proxy for employability. This was reiterated during the past weeks by Brian Leiter, who claimed in a series of (partly polemical) posts that there is “much correlation” between “PGR rank and overall tenure-track placement” (here), and that the PGR is an indispensable measure if one is interested in “academic employment” (here, read also Leiter’s important and sensible caveats).
As an aside, if the PGR indeed measures quality, and if it indirectly tracks (even predicts) hiring patterns, then we might also be inclined to think that the labor market for professional philosophers functions very well. One explanation for this may then well be the existence of the PGR, which provides prospective employers with crucial information (that would otherwise have been left un-aggregated) and, hence, becomes part of the causal nexus. One need not be a Hegelian (or Leibnizian, or Smithian) to appreciate the cunning of history that a self-proclaimed admirer of Marx is, in part, responsible for guiding the invisible hand of the market-place by aggregating expert judgments. Only in America, as my grandmother used to say. (I return to this below.)