Different Surveys, Different Results? A Comparison of Two Surveys on the 2009 European Parliamentary Election

Abstract

The European Election Survey (EES) is carried out in all member states at the time of each European Parliament election. The mode of data collection (mainly telephone interviews) and the sampling procedure (achieving 1,000 interviews in each country) raise doubts about the data quality. Until now knowledge has been lacking about the extent to which the mode of data collection and the sampling procedure bias the results. In one European country an independently designed election survey is carried out: The Swedish National European Parliament Election Study (SNES). The survey consists of face-to-face interviews of a random net sample of 2,682 individuals (response rate 67 per cent compared to 11.2 in the Swedish EES survey). In addition, SNES includes a large number of variables from official register data (including validated voting) that facilitates analyses without any non-responses generating missing data. This quasi-experimental methodological set up is used to compare the data from the two surveys for voter turnout, left–right placement and party choice. Results show that EES overestimates turnout levels more than SNES. EES also has a large overrepresentation of highly educated respondents, and thus underestimates differences in turnout between highly and less educated citizens. As for left–right placement, respondents in EES place both themselves and the parties on more extreme positions. Regarding party choice, the main difference between the surveys is that the EES largely underestimates the share of Social Democratic voters.