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The demand for and impact of learning HIV status: Evidence from a field experiment

Rebecca Thornton

Harvard University

11 November 2005

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It is commonly believed that HIV testing is essential for disease prevention. Indeed, spending on counseling and testing accounts for over half of the total expenditures on HIV prevention in some African countries. Despite this, there is evidence that even when testing is available most people do not take advantage of it, and there is virtually no persuasive evidence on the behavioral response to knowing one's status. For this paper, I designed and implemented a randomized experiment to evaluate the demand for learning HIV results and to estimate subsequent behavior change. In the experiment, over 2,700 individuals in rural Malawi were randomly assigned monetary incentives to learn their HIV results after testing. Two months later, they were re-interviewed and given the opportunity to purchase condoms. I find that while less than half of the participants attended clinics to learn their HIV status without any incentive, even a very small incentive (about one-tenth of a day’s wage) increased the share learning their results by 50%. Using the exogenously assigned incentives and distance from results centers as instruments for HIV knowledge, I find that HIV positive subjects with a sexual partner who learn their status purchase significantly more condoms; however, the average number of condoms purchased is low. Using these estimates, I calibrate an epidemiological model of infection that suggests that HIV testing is not as cost-effective as other prevention strategies; however, if testing services already exist, offering incentives may more effectively avert new infections.


Over the past two decades, the HIV/AIDS epidemic has afflicted Africa, with over 2.3 million AIDS related deaths and 25 million adults and children infected with HIV in 2001 (UNAIDS 2001). One suggested intervention to alleviate the spread of the disease is HIV testing, and some have gone so far as to declare that voluntary counseling and testing (VCT) is the “missing weapon” in the battle against AIDS (Holbrooke and Fuhrman 2004)1. Under the assumption that HIV testing is an effective prevention strategy, many international organizations and governments have called for increased investments into counseling and testing, requiring large amounts of monetary and human resources. For example, in South Africa, government expenditures on counseling and testing went from $2.4 million in 2000 to $17.3 million in 2004 and in Mozambique, 55 percent of the total expenditure on HIV/AIDS programs was spent on testing programs in 2000 (Martin 2003)2.

Underlying the emphasis on HIV testing for prevention – and the large expenditures on testing – are three rarely challenged assumptions: first, that there are important benefit to learning HIV results; second, that there are potentially large psychological and social barriers that prevent individuals from learning their HIV status; and third, that after learning HIV results, there are positive effects on sexual behavioral that prevent the spread of the disease, specifically, that those diagnosed negative will protect themselves from infection and those diagnosed positive will take precautions in order to protect others.

In this paper, I evaluate a randomized field experiment in rural Malawi that I designed and implemented to address these claims. I find that any barriers to learning HIV results can be easily overcome by offering small cash incentives. But, while there are significant behavioral effects after learning HIV positive results, the overall magnitude of the effects are small. Relative to other available prevention strategies, HIV testing is not the most cost-effective way to avert the most infections with a given budget. However, if testing services already exist, offering small rewards to encourage people to learn their results may inexpensively reduce the spread of HIV.

Previous studies have attempted to measure the demand for learning HIV status, as well as the subsequent behavioral effects after learning HIV results. Most studies rely on self-reported behavior by asking individuals if they want to know their HIV status (e.g., Day et al. 2003, deGraft-Johnson et al. 2004, Laver 2001 and Yoder 2004) or asking about sexual behavior (e.g., Coates et al. 2000; Kamega et al. 1991, Temmerman et al. 1990, and Weinhardt et al. 1999). Self-selection is also a serious limitation to evaluating the effects of learning HIV results. Most, if not all, studies use a sample of individuals who self-select into knowing their status. One exception to this is a study that randomly phased individuals into being tested (Coates et al. 2000). Their findings that learning HIV results substantially reduced reported risky sexual behavior has since been widely cited within the public health literature and used in subsequent simulations to conclude that counseling and testing is an effective strategy for preventing new infections (Sweat et al. 2000). However, even the study by Coates and his colleagues was conducted among self-selected individuals who choose to have an HIV test at urban health clinics and relied on reported sexual behavior as the measure of behavioral change.

The design of this experiment avoids the usual complications of selection bias and reporting errors because it measured actual attendance and condom purchases, randomized the location of centers giving results, and randomized individual incentives to learn HIV status. This is important because factors impacting the decision to learn HIV results are generally correlated with behavioral outcomes, leading to biased estimates of the impact of learning HIV results on sexual behavior.

Respondents in rural Malawi were offered a free HIV test and were given randomly assigned vouchers between zero and three dollars, redeemable upon learning their results. I find that the demand for HIV information without incentives was moderate: 39 percent of those given no monetary incentive attended centers to learn their results. However, learning HIV results was highly elastic and those receiving positive-valued incentives were, on average, twice as likely to learn their HIV status as those receiving no incentive. Although the average incentive was worth about a day’s wage, even the smallest amount, one-tenth of a day’s wage, resulted in large attendance gains. The location of each results center was also randomly placed to evaluate the impact of distance on attendance: living over one kilometer from the VCT center reduced attendance by eight percent. There is also evidence of strategic complementarities of neighbors’ and spouses’ attendance with respondents own attendance.

Several months later, follow-up interviews were conducted and respondents were given the opportunity to purchase condoms. Using the random allocation of incentives and distance as exogenous instruments for learning HIV status, I find that receiving an HIV positive diagnosis significantly increased the likelihood of purchasing condoms among those with a sexual partner. Learning HIV status had no impact among those that were HIV negative or those who were not sexually active, and there are no additional effects when both members of a married couple learn their HIV status.

Given the estimated effects of learning HIV results on the demand for condoms and epidemiological parameters determining disease transmission, I estimate the cost-effectiveness of HIV testing in terms of expected new infections averted and associated costs. Compared to cheaper prevention programs, I find that testing is not a cost-effective strategy for averting infections. However, if governments or organizations do choose to adopt HIV testing as a prevention strategy, or if there are existing testing services, offering small rewards to encourage people to learn their results may be effective.

The paper proceeds as follows: Section 2 discusses the study design. Section 3 presents the impact of incentives and distance on learning HIV status. Section 4 presents the effects of learning HIV status on sexual behavior. Section 5 evaluates cost-effectiveness. Section 6 concludes.

  1. Several organizations such as the Global Business Coalition, WHO, UNAIDS, Viacom, the Henry J. Kaiser Family Foundation, and the Bill and Melinda Gates Foundation have begun investing in large-scale international media campaigns to increase testing (Global Business Coalition 2005; 2005).
  2. Although testing is currently conducted among voluntary clients, mandatory testing has been widely discussed as a prevention strategy (Reporter 2004, Lafraniere 2004, Nyathi 2003).

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