The Effect of Survey Mode and Sampling on Inferences about Political Attitudes and Behavior: Comparing the 2000 and 2004 ANES to Internet Surveys with Nonprobability Samples

Since the inception of the American National Election Study (ANES) in the 1940s, data have been collected via face-to-face interviewing in the homes of members of area probability samples of American adults, the same gold-standard approach used by the U.S. Census Bureau, other federal agencies, and some nongovernment researchers for many of the most high-profile surveys conducted today. This paper explores whether comparable findings about voters and elections would be obtained by a different, considerably less expensive method: Internet data collection from nonprobability samples of volunteer respondents. Comparisons of the 2000 and 2004 ANES data (collected via face-to-face interviewing with national probability samples) with simultaneous Internet surveys of volunteer samples yielded many differences in the distributions of variables and in the associations between variables (even controlling for differences between the samples in reported interest in politics). Accuracy was higher for the face-to-face/probability sample data than for the Internet/volunteer sample data in 88% of the possible comparisons. This suggests that researchers interested in assuring the accuracy of their findings in describing populations should rely on face-to-face surveys of probability samples rather than Internet samples of volunteer respondents.