# **Interpretation**

Many child health studies of water, sanitation, and hygiene interventions have been smallscale, short-duration efficacy trials [41]; these trials are an essential step in documenting the potential for interventions to impact child health, but ultimately the external validity of such studies remains open to debate. This study was designed to measure the impacts of one of the largest public health interventions in human history: India’s TSC has touched the majority of rural Indian households since its inception in 1999. Effectiveness studies that measure the impact of large-scale government programs face numerous challenges compared to tightly controlled efficacy trials. A central challenge is ensuring good compliance and high fidelity of intervention implementation. In this study, we found evidence of TSC activities in 10 of 40 control villages, and in no case did intervention villages achieve “Open Defecation Free” status. Although a finding of incomplete implementation is an important finding in itself, ITT estimates of program impacts with imperfect compliance will tend to underestimate the effect possible under perfect compliance. If the effects of rural toilet promotion campaigns are heterogeneous with villagelevel toilet coverage, then this study provides information only about conditions where toilet coverage is < 80% (with most villages closer to 40%). In theory, the effects of similar interventions on child health could be larger if intervention campaigns achieve higher levels of toilet coverage, but the question can only be answered empirically in future studies that achieve higher levels of toilet coverage in intervention villages and allow for a longer duration of program exposure.

A second challenge in studying large-scale programs that are not implemented by evaluation investigators is that implementation timelines may differ greatly from the original evaluation timeline. The follow-up measurement in this study (21 months following baseline) was the latest possible point we could measure outcomes under the grant timeline and our expectation that the program would soon expand into control villages. Although it is possible that impacts on diarrheal disease could begin relatively soon after intervention, as documented in short-duration efficacy trials [41], we would expect impacts on intestinal parasite infection and growth to potentially accrue more slowly. _Ascaris_ ova are viable in the environment for many months (possibly years) [42]; for this reason, the hygienic disposal of feces may require many months to measurably reduce the quantity of viable helminth eggs in the village environment and subsequent parasite infection. Similarly, we would expect any benefit of sanitation interventions to child height to require many months of exposure to improved conditions since the causal mechanism is thought to work through a cumulative reduction of symptomatic and asymptomatic infections over the first years of life [13,43]. Given the large improvements in toilet construction documented in this study, an additional child health follow-up measurement in the study villages would yield valuable information over a longer period of exposure to improved sanitation conditions.

To provide some context to our results, we reviewed findings from recent studies of similar sanitation programs. Our findings contrast with the preliminary results reported in two working 18 / 41