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Unformatted text preview: IV test (Table 1, panel B). See also Francis Obare (2006). Among the main sample who
agreed to be tested, 18 percent reported having been tested previously for HIV, although only
half of these individuals reported actually receiving their results. Those who reported having a
previous test were 6 percentage points more likely to agree to be tested by the MDICP nurses
(Table 1, panel B). Not all spouses of respondents were offered a test: men who divorced or whose
spouse died and spouses of the newly sampled adolescents were ineligible for testing.
While attrition from the panel across years suggests that the sample has disproportionately
fewer mobile individuals—perhaps leading to a downward bias in the HIV prevalence rate and
posing a potential threat to external validity—the sample who accepted an HIV test is relevant
from a policy perspective in that it represents those who would be present during an HIV testing
campaign in rural areas.
The follow-up interviews were conducted among 75 percent of those in the main sample in
Balaka and Rumphi. Learning HIV results and HIV status itself are both separately associated 1838 THE AMERIcAN EcONOMIc REVIEW DEcEMBER 2008 with attrition from the follow-up survey. Being HIV-positive increases the likelihood of attrition
by 17 percentage points, which could be due to death or sickness (Table 1, panel C). Having
obtained HIV results from the VCT center decreases the likelihood of attrition by 24 percentage points, which to a certain extent is mechanical since those who were available to attend the
VCT center were also more likely to be available for the follow-up interview (if, for example,
they had not temporarily migrated). Importantly, all exogenously assigned variables (receiving
an incentive, the amount of the incentive, and the distance from home to the VCT center) have no
significant direct effect on likelihood of attrition at the follow-up. Thus, while sample attrition
and HIV test refusals may pose a potential threat to the external validity of the study, the lack of
differential attrition associated with incentives or distance minimizes risk to the internal validity
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