At least 5 percent of American men, I estimate, are predominantly attracted to men, and millions of gay men still live, to some degree, in the closet. Gay men are half as likely as straight men to acknowledge their sexuality on social networks. More than one quarter of gay men hide their sexuality from anonymous surveys. The evidence also suggests that a large number of gay men are married to women.

There are three sources that can give us estimates of the openly gay population broken down by state: the census, which asks about same-sex households; Gallup, which has fairly large-sample surveys for every state; and Facebook, which asks members what gender they are interested in. While these data sources all measure different degrees of openness, one result is strikingly similar: All three suggest that the openly gay population is dramatically higher in more tolerant states, defined using an estimate by Nate Silver of support for same-sex marriage. On Facebook, for example, about 1 percent of men in Mississippi who list a gender preference say that they are interested in men; in California, more than 3 percent do.

Are there really so many fewer gay men living in less tolerant states? There is no evidence that gay men would be less likely to be born in these states. Have many of them moved to more tolerant areas? Some have, but Facebook data show that mobility can explain only a small fraction of the difference in the totally out population. I searched gay and straight men by state of birth and state of current residence. (This information is available only for a subset of Facebook users.) Some gay men do move out of less tolerant states, but this effect is small. I estimate that the openly gay population would be about 0.1 percentage points higher in the least tolerant states if everyone stayed in place.