Participant attrition is a major concern for the validity of longer or complex surveys. Unlike paper-based surveys, which may be discarded even if partially completed, multi-page online surveys capture responses from all completed pages until the time of abandonment. This can result in different item response rates, with pages earlier in the sequence showing more completions than later pages. Using data from a multi-page online survey administered to cohorts recruited on Reddit, this paper analyses the pattern of attrition at various stages of the survey instrument and examines the effects of survey length, time investment, survey format and complexity, and survey delivery on participant attrition. The participant attrition rate (PAR) differed between cohorts, with cohorts drawn from Reddit showing a higher PAR than cohorts targeted by other means. Common to all was that the PAR was higher among younger respondents and among men. Changes in survey question design resulted in the greatest rise in PAR irrespective of age, gender or cohort.