The quality of data in surveys is affected by response burden and questionnaire length. With an increasing number of questions, respondents can become bored, tired, and annoyed and may take shortcuts to reduce the effort needed to complete the survey. In this article, direct evidence is presented on how the position of items within a web questionnaire influences respondents' focus of attention. In two experiments, part of an eye-tracking study and an online survey, respectively, a variety of indicators show that data quality is lower if the experimental question is positioned at the end rather than at the beginning of a questionnaire. Practical implications are discussed.