Chong et al.

14

**Table 6.** Friendship Networks Summary Statistics

|||**Cases**|**Percent**|
|---|---|---|---|
|**Treatment students with:**|No friends treated|366|21.2%|
||1 friend treated|277|16.0%|
||2 friends treated|266|15.4%|
||3 friends treated|227|13.1%|
||4 friends treated|286|16.6%|
||5 friends treated|183|10.6%|
||6 friends treated|123|7.1%|
|**Spillover students with:**|No friends treated|1482|88.8%|
||1 friend treated|133|8.0%|
||2 friends treated|11|0.7%|
||3 friends treated|7|0.4%|
||4 friends treated|7|0.4%|
||5 friends treated|13|0.8%|
||6 friends treated|15|0.9%|

_Source_ : Authors’ analysis from student surveys. _Note_ : Friendship link treatment status is established by matching self-reported list of friends with list of names of students answering the survey at (either) follow-up survey. The number of friends treated for students in control schools is equal to zero.

students, a 55 percent increase in redemption ( _p_ = 0.07). The study puts substantial weight on this result as it provides objective evidence of an increase in condom demand. In unreported results, the estimated coefficient is basically unchanged when controlling for distance to the health clinic.

As a robustness check, bounding exercises were performed with differing assumptions on attrition, as in Karlan and Valdivia (2011), and found that the positive effect on condom voucher in table 5 (0.099 percentage points; standard error = 0.055 percentage points) still holds after imputing the mean minus 0.10 standard deviations of the observed treatment distribution to the nonrespondents in the treatment group, and after imputing the mean plus 0.10 standard deviations of the observed control distribution to nonrespondents in the control group.<sup>20</sup>

# Friendship Network Spillovers and Reinforcing Interactions

Next the study takes advantage of the fact that in the surveys students were asked to identify their closest friends by name, and indicate if they were in the same school and/or classroom. This information is used to match each student’s social network to the list of students in the treatment and spillover groups. This makes it possible to analyze treatment and spillover effects differentiating between students for whom a small or a large percentage of friends was also treated.

Table 6 presents summary statistics about the network treatment distribution. For 21 percent of students in a treated classroom their list of friends does not contain anyone from their own classroom. The analysis will consider these students as having a network of friends that is not treated at all. In contrast, 79 percent of students in a treated classroom have at least one friend in their own classroom (who was hence also treated). The table shows substantial variation in the number of friends that are located in the same classroom as a treatment student. The lower panel in the table shows that for students in a spillover classroom, there are few links to students taking the course (in the treatment classroom). Indeed, 89 percent of spillover students have no friends in the treatment classroom—this will affect the precision of the spillover estimates.

20 Results of these simulations are not presented here but are available upon request.