The authors tested whether questions about sexuality showed "evidence of social desirability bias even when asked in a self-administered, computer-assisted survey."

Their findings: Yes, even in 2012, and "even under extreme privacy and anonymity."

The veiled method increased self-reports of non-heterosexual identity by 65 percent, same-sex sexual experiences by 59 percent, and directionally same-sex attraction by 9.4 percent. We combine all own-sexuality questions into an index, and find that the Veiled Report treatment significantly raises the number of sensitive answers overall. The veiled method also increased the measured rates of anti-gay sentiment. Respondents were 67 percent more likely to express disapproval of an openly gay manager at work, 71 percent more likely to say it should be legal to discriminate in hiring on the basis of sexual orientation, 22 percent less likely to support the legality of same-sex marriage, 46 percent less likely to support adoption by same-sex couples, and 32 percent less likely to state they believe homosexuality is a choice. We again combine all the opinion questions into an index, and find that the Veiled Report treatment significantly raises the overall number of intolerant answers. Taken together, these results indicate that both non-heterosexuality and anti-gay sentiment are substantially underestimated in existing surveys.

Those results would seem to be mutually reinforcing and suggest that people know that there is more anti-gay bias than is generally admitted these days and so are extremely reticent to admit to having had same-sex experiences, especially if they do not identify as gay or lesbian.

The sample was not a representative one and so can't be taken to show the full extent of opinion or behavior in these areas—only that traditional survey methods aren't picking them up accurately, even among a fairly young and not wildly conservative sample. Those surveyed had a median age of 26, and less than 16 percent said they were Republicans.

Because they were measuring stigma, the authors postulated that "under reporting of non-heterosexuality in the Direct Report treatment ... should be larger for demographic groups with social norms that are perceived as less LGBT-friendly: Christians, older respondents, and Black/African Americans." And that's in fact what they found:

Among Christians in our sample, the Veiled Report condition raises reports of non-heterosexuality by 13 percentage points (from 8 to 21 percent) in Question 1 and same-sex sexual experience s by 14 percentage points (from 11 to 25 percent) in Question 3, compared to the Direct Report. These are increases of 163 and 127 percent, respectively. Among participants with no religious affiliation, the Veiled Report treatment produces much smaller differences in these questions.

In short, though surveys show growing support for LGBT rights, there's still plenty of bias below the surface.

We want to hear what you think about this article. Submit a letter to the editor or write to letters@theatlantic.com.