Because of costs and time reduction, the Internet is more and more used to conduct surveys. However, moving from traditional modes of data collection to the Internet may threaten the comparability of the data (longitudinally or across groups) if the mode of data collection has an impact on the way of answering the questions of the respondents. In previous research, Revilla and Saris (2010) find similar average quality for several survey questions when asked in a face-to-face interview or when asked in a Web questionnaire. But does that mean that the mode of data collection does not have an impact on the quality? Or may it be that for some respondents the quality is higher in Web whereas for others it is lower, such that in average the quality for the complete sample is similar? To answer these questions, this paper compares the quality for different groups of respondents (depending on age, gender, education) both of a face-to-face survey (European Social Survey round 4) and a Web survey (LISS panel).