The effectiveness of incentives is well-documented in the literature (e.g., Church, 1993; Singer, 2002). Cash incentives are both cost-effective and easy to deliver in face-to-face surveys, or as prepaid incentives enclosed with advance letters. For larger amounts—typically used with conditional incentives—checks are often used. The cost of processing and mailing a check can be relatively expensive, especially for small incentive amounts delivered frequently.  In online panels, the use of lotteries or rewards points is common, in part because of the cost of delivering repeated incentives of small value (Göritz, 2006). Unfortunately these incentives are often less effective than cash.