# **S.1 Cost-effectiveness analysis of solar lanterns on school attendance**

To further assess the estimated impacts on school attendance, we carried out a cost-effectiveness analysis, following the method used by Dhaliwal et al. (2013) and Evans and Popova (2016). Table S.15 in this supplemental appendix reports on additional years of education per 100 USD, based on the estimated treatment effects reported in columns (d) and (h) in Table 6 in the article. To simplify the analysis, we considered only the cost (prices) of the solar lanterns, ignoring other factors such as research administration costs, reduced kerosene expenditure, and product maintenance opportunity costs. Assuming that the life of a solar lantern is five years, the minimum length of time for which products function effectively in normal conditions, we divided the product prices by five to estimate annual product costs. Table S.15 shows that our intervention raised student participation by 0.59 and 0.64 years per 100 USD spent with and without baseline control.<sup>23</sup> This table also shows that providing a bundle of three lanterns is more cost effective than providing only one solar lamp; however, the estimated solar impacts were only marginally different between the two cases at 10―15% significance levels, as reported in Table 6 in the article. While the impact of our intervention did not last long, this increase of 0.59―64 years per 100 USD still seems remarkable. Referring to Evans and Popova (2016) (Table 3 in p. 268), this increase can be compared with that revealed in Evans et al. (2008)’s study, which involved distributing school uniforms in Kenya.

# **S.2 Discussion: does complementarity matter?**

A growing body of empirical research has suggested that relaxing only one educational constraint may not result in children’s improved school outcomes in the developing world (e.g., Glewwe et al. 2004; Glewwe et al. 2009; Mo et al. 2013). Given that solar lamps were also expected to address only one factor that encouraged children’s human capital acquisition, i.e., better nighttime lighting for home study, our findings are consistent with those provided by recent studies. Our findings are also in line with the experimental study conducted in Uganda by Furukawa (2014), who also revealed no improvement in school exam outcomes despite the increased study time induced by the provision of solar lanterns.<sup>24</sup> Complementarity across educational inputs (e.g., textbooks, teacher quality, and home-study support) may play an important role in determining academic performance. For example, in the estimations of school attendance performed in Table 6 in the article, we saw statistically significant increases in school attendance in the first two visits for the treated students (mainly for those who received all three solar products). However, during the final visit in August,

> 23More precisely, these figures came to:

> (solar impacts _×_ no. of treated students) _÷_ ( <u>product5pyearsrices (USD)</u> _×_ no. of treated students) _×_ 100 USD.

> 24Furukawa (2014) indicated that the malfunctioning of the solar products (due to flickering and failure to fully recharge the unit) might have made nighttime study virtually impossible for the treated students, thus resulting in an insignificant impact. However, our counterpart NGO, which had continuous contact with the subjects in the studied area, did not report this problem.

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