Increasingly, researchers have experimented with the use of CCT and/or CM in preventing HIV and other sexually transmitted infections (STI), with mixed results. Kamb and others (1998) examined the differential impact of small monetary incentives versus other types of incentives (e.g. grocery coupons) on enrolment and participation in an HIV/STD prevention counseling intervention. 55 percent of enrollees offered cash completed the program, compared to only 37% of those offered other incentives. However, regardless of the type of incentive provided, enrollees experienced similar STD rates at follow-up. Petry (2001) experimented with a group based CM intervention offered at increasing frequency at an HIV drop-in center which provided a reward for attending group sessions and completing steps related to treatment goals. Attendance increased significantly in response to the frequency of reward, and the percentage of treatment activities completed rose from 25% at baseline to 65% during intervals of more frequent rewards.

It has also been suggested that CM could be effective at improving adherence to anti-retroviral (ARV) therapy (Haug and Sornesen, 2006). In fact, a U.S.-based study of 56 HIV-positive patients with histories of illicit substance abuse and had shown suboptimal adherence during a baseline assessment found that a brief CM-based intervention was associated with significantly higher adherence and lower viral loads, compared to supportive counseling only. However, by the end of the 16-week follow up phase, differences in adherence and viral load between the two groups was no longer significantly different.

Finally, Thornton (2006) conducted a cluster randomized control trial of individuals who were tested for HIV in a VCT clinic in rural Malawi. Individuals were randomly assigned voucher payments ranging in value between $0 and $3 to be paid when test results became available. The experiment found that participants were very responsive to even small amounts of cash. The cash payment increased the number of individuals returning to collect their test results by a mean of 27 percent, after controlling for distance. In addition, each extra dollar paid resulted in a 9 percent increase in the number of individuals returning to collect test results.

Arguably, each of the above examples used cash incentives to encourage a relatively simple behavioral change – participation in educational sessions, completion of target goals for treatment, adherence to medications, and showing up to retrieve test results. However, the ultimate goal of HIV prevention is to discourage risky sexual practices in order to stop the spread of the AIDS virus. For this, it makes sense to more closely align the incentive with the target behavior. In other words, for maximum effect, the cash incentive should reward safe sexual practices, and discourage risky ones.

Of course, sexual activity, risky or otherwise, is not an observable behavior, so a proxy is required. A cash transfer that is conditional on remaining HIV negative is, perhaps surprisingly, not ideal. It would be ethically questionable to impose this conditionality, as it would represent a “double-whammy” for individuals to be denied the cash payment in conjunction with having been just diagnosed with HIV. In addition, as HIV is a rare event and has a long incubation period, such a contingency is likely to be too far distant from the behavior needing to be reinforced (e.g. safe sexual behavior). Thus, a more reasonable proxy would be the condition of remaining free of sexuallytransmitted infections that are prevalent within the population, have been incontrovertibly linked to risky sexual activity, and can be easily treated and cured. Examples of curable 12