Usability testing is a critical tool for evaluating computerized data collection instruments. Usability testing is especially informative for self-administered instruments used to collect data on the Web, since Web survey design is often motivated by demands for quick turnaround data collection and the needs of programmers, rather than needs of survey respondents. Many of the standard tools for Web survey design, such as drop-down menus and radio buttons, may make answering questions difficult for respondents and contribute to measurement error. This paper will analyze the results of usability tests of three different types of self-administered Web data collection instruments: a web survey, a time and activities diary, and a food diary. Based on these results, we will suggest techniques to improve the usability of Web data collection instruments.