Using its nationally representative American Trends Panel, Pew Research Center conducted a large-scale experiment that tested the effects of the mode of survey interview – in this case, a telephone survey with an interviewer vs. a self-administered survey on the Web – on results from a set of 60 questions like those commonly asked by the center’s research programs. This report describes the effort to catalog and evaluate mode effects in public opinion surveys.
The study finds that differences in responses by survey mode are fairly common, but typically not large, with a mean difference of 5.5 percentage points and a median difference of five points across the 60 questions. The differences range in size from 0 to 18 percentage points. The results are based on 3,003 respondents who were randomly assigned to either the phone or Web mode and interviewed July 7-Aug. 4, 2014 for this study.
Where differences occurred, they were especially large on three broad types of questions: Items that asked the respondent to assess the quality of their family and social life produced differences of 18 and 14 percentage points, respectively, with those interviewed on the phone reporting higher levels of satisfaction than those who completed the survey on the Web.
Questions about societal discrimination against several different groups also produced large differences, with telephone respondents more apt than Web respondents to say that gays and lesbians, Hispanics and blacks face a lot of discrimination. However, there was no significant mode difference in responses to the question of whether women face a lot of discrimination.
Web respondents were far more likely than those interviewed on the phone to give various political figures a “very unfavorable” rating, a tendency that was concentrated among members of the opposite party of each figure rate