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Unformatted text preview: ; Elaine Sieff, Robyn M. Dawes, and Loewenstein 1999).
Not controlling for this simulated average term would ignore the fact that each VCT zone is bounded and that, in
expectation, more central households have shorter distances to travel from any randomized location (although including
this term does not significantly change any of the estimates).
The VCT centers were placed throughout the study site such that many villages were assigned to the same center—this ranged from as few as 3 villages at one center (in Balaka) to as many as 14 villages attending another center
(in Rumphi). Clustering standard errors by VCT center, rather than village, reduces the standard errors on the impact
of incentives, but increases the standard error of the effect of distance on attendance. The results are not significantly
different when using larger clusters. Also, because there were only 16 VCT centers, there may be omitted variables
correlated with the center location that may be systematic, despite the randomized design. The results do not change
significantly, however, if VCT center fixed effects are included (not shown). 1840 DEcEMBER 2008 THE AMERIcAN EcONOMIc REVIEW
1 Percentage learning HIV results 0.9
0 No incentive Some incentive A. Effects of receiving some incentive 1 Percentage learning HIV results 0.9
0 0 0.1– 0.2 0.3 –0.5 0.5 –1.0 1.0–1.5 1.5–2.0 2.0– 2.5 2.5–3.0 B. Effects of the total amount of the incentive
Figure 3. Percentage Returning for HIV Results
Notes: Sample includes 2,812 individuals who tested for HIV; 0.05 percent error bars are presented. Figures present the
percentage of individuals attending HIV results centers. incentive, a difference of 43 percentage points (Table 4, column 1). Moreover, the probability of
center attendance increased by an additional 9.1 percentage points with every additional dollar of
incentive (Table 4, column 2), with the nonlinear effect of the incentive also imp...
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