Be careful when interpreting survey data. People do not always tell the truth about what they know and what they do.
One-in-six (16%) of those who say they “definitely voted” in the 2014 midterm election have no record of voting in commercially available national voter files, according to a Pew Research Center analysis.
One likely reason for at least some of this mismatch is the tendency for people to over-report “good” behaviors, such as voting, giving to charities, or attending religious services, while underreporting unattractive behaviors, such as drug and alcohol abuse. This phenomenon is known as the social desirability bias.
Another likely reason for the mismatch, as past research has found, is that the voting record for some people who actually voted is missed by commercial voter files. This happens most often for people who have recently moved. This error may have implications for campaign pollsters who rely on previous voting history in voter files to draw samples of likely voters or to help predict future voting behaviors.