Lying or confused respondents is a common challenge that social scientists have consistently had to deal with over the decades. The very best psychology or sociology studies actually don’t rely on self-reported analysis and instead try to rely on direct observation because of a phenomenon known as “social desirability bias,” or the tendency of people in any social situation to give what they believe to be the viewpoint that is the most popular.

Social desirability bias was first noted by political science researchers in the 1982 California governor’s race. Days before the election, most polls reported that black candidate Tom Bradley was ahead of his white opponent, George Deukmejian. Surveys conducted on the day of the vote also indicated that Bradley would win. That proved untrue, however, because a least some white respondents appear to have falsely told pollsters that they would be supporting Bradley. Thereafter, the idea that white support for a black candidate might be lower than surveys indicated was colloquially called the “Bradley Effect.”

In the UK, social desirability bias is called the “Shy Tory Factor” because supporters of the Conservative Party have been observed for many decades to be less willing to tell pollsters that they would be voting for it. In 10 of the last 12 British elections, polls underrated the Tory vote. A similar skew was observed in the recent Brexit vote when the average of the final surveys indicated that “Leave” support stood at 44.3 percent. In the actual tally, Leave won with 51.9 percent. In France, a similar accuracy problem has been observed as well where polling has overstated the support of left-leaning parties and understated the support of nationalist parties.