The increasing use of data collection online (instead of off line) creates a need for research on the factors that affect compliance and data quality in web based surveys. In general, surveys should be clean, concise and appealing (Dillman, 2000) so that participants’ motivation to complete the survey increases or at least not decreases over the course of the survey. Intuitively, one would argue that a progress bar is such a motivating factor: it gives the participant insight into the length of time the survey will take, and in particular a sense that the survey will not ask for too much of their time. Nevertheless, the few studies that have tried to corroborate this hypothesis found mixed results. Both Couper et al. (2001) and Crawford et al. (2001) even found a negative effect of the existence of a progress bar on completion rates, although there were some methodological issues that may have been the reason for this surprising finding (as they mention themselves, Couper et al. did not control for download times and Crawford et al. may have made a miscalculation in the prediction of the remaining questions). Recent research by Boehme (2003) shows no effect of the progress bar on completion, but does find some effects when comparing progress bars that are either degressive or progressive. We continue this line of research, focusing on the length of the survey as an intervening variable. Using a sample of 3556 respondents of the Dutch PanelClix online panel, we compare the effects of different kinds of progress bars on survey compliance and data quality. We indeed find that the length of the survey is an important factor when it comes to determining the usefulness of progress indicators. Boehme, R. (2003) Fragebogeneffekte bei Online-Befragungen. Master’s Thesis in Communication Science. University of Dresden. Couper, M. P., Traugott, M. W. & Lamias, M. J. (2001). Web survey design and administration. Public Opinion Quarterly, 65 (2), 230-253. Crawford, S. D., Couper, M. P. & Lamias, M. J. (2001). Web surveys: Perceptions of burden. Social Science Computer Review, 19 (2), 146-162. Dillman, D. A. (2000). Mail and internet surveys: The tailored design method (2nd edition). New York: Wiley.