Bigelow, 1983, 1984), at least during the treatment period; the effect appears to weaken during follow up (Higgins and others, 2007). However, the magnitude of incentive required for shaping sexual behavior is unknown. Preliminary assessments can be obtained through focus group discussions, survey data, and discrete choice experiments, but these are no substitute for direct measures of impact achieved by randomly assigning different sized payments to individuals participants, as was done in the Malawi study (Thornton, 2006).

A separate but related consideration is the frequency and immediacy in which the cash incentive is paid out. Given the unplanned and spontaneous nature of many sexual encounters, the incentive needs to be offered frequently enough to keep it ever-present in the minds of the target group, and as immediately as possible to reinforce the link between the payment and the target behavior. It seems reasonable to assume, and the CM literature has confirmed (Stizer and Petry, 2006), that larger cash payments given frequently have greater impact than smaller payments given less frequently, but it is nevertheless unclear how these two dimensions of magnitude and frequency interact.

Of additional interest is whether the cash incentive should be paid directly to individuals, to a couple, or some other social grouping. CCT programs for poverty alleviation have tended to target households and communities, but the incentive is actually paid to the mothers of young children, rather than the fathers or the legal headof-household. This design feature has been a nod to a series of findings that women are more likely to use the money on food for the family rather than on alcohol or other purchases (Rawlings and Rubio, 2005, Schady and Rosero, 2007). However, some studies of CM interventions have found that the effect size of incentive was greatest if the payment was made to a pre-designated group rather than the individual (Jeffrey 1983). This may be due to the social support provided by the group, or peer pressure, or some combination, and the question is whether such a mechanism can or should be applied to the sexual relationship.

Relatedly, there is the question of whether the cash incentive should be given alone or in conjunction with a psycho-social or counseling component. A study of California teens on welfare found that teens who received counseling in addition to cash were slightly more likely to complete high school than those receiving either cash or counseling alone (UCDATA). Several studies of CM interventions offered singly and in conjunction with counseling also found that the combination appeared to have greater impact (Krishnan-Sarin and others 2006). However, the effects were small, and the question of whether the additional programmatic costs involved in adding a counseling component were justified was not resolved.

# _Implementation_

CCT programs for poverty alleviation have already been brought to scale in several different settings, and therefore have broken the credibility barrier by proving that it can be done. Of course, this has not eliminated concerns about whether CCT programs will be equally effective in other settings, particularly those where initial infrastructural investments in schools and health clinics are very low, as in many countries in SubSaharan Africa (Lagarde, Haines, and Palmer, 2007). However, some important initial groundwork has been laid, such as assessments of the type of infrastructural support that is needed to administer these programs, and associated costs. Nonetheless, the cost14