NCBI ROFL: Apparently, you can't bribe doctors with candy.

Randomized trial of 5 dollars versus 10 dollars monetary incentives, envelope size, and candy to increase physician response rates to mailed questionnaires. "BACKGROUND: The validity of the results of mailed surveys is often threatened by nonresponse bias, which is made more likely when response rates are low. However, the effectiveness and cost-effectiveness of several strategies to increase response rates are uncertain. OBJECTIVES: To assess three strategies to increase response rates to mailed physician surveys: including a 10 dollars versus a 5 dollars cash incentive in the initial mailing, including a mint candy or not, and using a large versus small outgoing envelope. RESEARCH DESIGN AND SUBJECTS: Using a 2 x 2 x 2 factorial design, a randomized trial of these strategies was conducted in a survey of 1200 physicians randomly selected from the American Medical Association's Master File RESULTS: Including a 10 dollars incentive yielded a significantly higher response rate ...