Two recent post by Jim and Jens ponder the holy grail of manipulability via the exchange between Holland and Heckman. Can non-manipulable things like gender or race cause things in the potential outcomes framework?
Holland (1986) says no because it’s hard to conceive of changing the unchangeable. Fair enough. But this argument has been carried too far in some quarters and not far enough in others. Here’s why:
Invoking Holland, some population scientists now go so far to claim that we can’t conceive of things like marriage or divorce as causes because the decision to marry or divorce is beyond the direct control of an experimenter. Please. At most we need some exogeneity, a little speck of indifference, a tipping point to make them amenable to coherent causal thinking (and estimation). Heckman goes even farther than this, and he is right: the issue is not whether I, personally, can wreck all marriages in my study, but whether we can coherently conceive of a counterfactual world where things are different as a matter of theoretical speculation ("mental act"). In this, however, even Heckman seems to yield: A minimum requirement for thinking about counterfactual worlds would appear to be the possibility of conceiving of these worlds in a coherent fashion. And this, I believe is the underlying unease of the statisticians whom Heckman criticizes: whether one can even coherently imagine counterfactual worlds in which gender is changed.
On the other hand, social scientists love to talk about the effects of gender and race, which – pace Michael Jackson and Deidre McCloskey – are really hard to think of as manipulable, ceteris paribus. What Holland’s dictum contributes in this respect is the entirely appropriate call for getting the question straight.* For what most of these studies look for is evidence of discrimination. Thinking about discrimination within the potential outcomes framework makes it clear that the issue really isn’t whether we can manipulate the race or gender of a specific person, but rather whether we can manipulate the perception of the person’s race or gender in the eyes of the discriminator. Cases in point: Goldin and Rouse’s study on discrimination in symphony orchestras, where the gender of applicants was obscured (i.e. perceptions manipulated) by staging auditions behind an opaque gauze barrier. Similarly, Grogger and Ridgeway’s paper in the latest issue of JASA uses natural variation in the perceptibility of driver’s skin color (dusk, the veil of darkness) to test for racial profiling in traffic controls. In either case, the causal question was not, what would happen if we changed the musician/driver from female/black to male/white, but, What would happen if we could change knowledge/perception of race and gender.
In other words, there are important causal questions to be asked about race and gender, but these questions don’t necessarily require the manipulability of race and gender. Not even within the potential outcomes framework of causality.
* My pet peeve: Much of social science is so busy providing answers that it forgets to ask well-formulated questions.