Participants and sampling
SECONDARY
The population of interest for the study was children 0–35 months old and their caregivers. We focused on this population because children 0–35 months old at the time of endline data collection in early 2019 would have been exposed to the project during at least part of the 1000‐day window, given the project was largely implemented between 2014 and 2018. Because the key project outcomes were focused on populations at a particular stage in life, we used a repeated cross‐sectional approach, drawing a different random sample of children 0–35 months old at baseline and endline.To identify the villages for household sampling, we randomly selected four villages in each treatment and control subdistrict as the primary sampling units (PSU), a total of 760 villages. In a small number of subdistricts, we added an additional village at baseline because the original four were insufficient to meet sample targets, resulting in a total of 767 villages in the baseline sample. All children 0–35 months old and their caregivers in the sampled villages were eligible for the study sample. The original 760 villages selected at baseline remained the PSUs for the endline data collection. However, we added 26 randomly sampled villages at endline to bring us closer to sample size targets, resulting in a total of 786 villages in the endline sample. To mitigate the costs of conducting a household listing in large villages, if the population of a sampled village was larger than a preestablished cutoff based on sample size targets (250 households at baseline and 400 at endline), we determined the appropriate administrative level to use as the secondary sampling unit (SSU) and developed a list of these SSUs with the help of the village head. We then randomly selected one SSU in each PSU; in a few cases, we selected an additional SSU because the selected one was insufficient to meet sample size targets. The baseline and endline surveys were therefore conducted mostly in the same villages (PSUs) but in different SSUs.Because many expected synchronicities in project activities did not materialize due to implementation delays, project exposure varied substantially across cohorts of children. The primary sample of interest comprised children who were 24–35 months old at endline, because they would have received the most exposure to the project activities in the 1000‐day window, as we discuss below. The endline sample therefore included 4560 children 24–35 months old at endline, which we complemented with a smaller sample of 3040 children 0–11 months old (to capture pregnancy and newborn care behaviours, which were unlikely to be accurately recalled for older children) and 1520 children 12–23 months old (to round out the sample of children to cover the full 0–35‐month age range with at least partial exposure). This amounted to a total sample size of 9120 households (about 12 per village). We estimated that this sample size would enable us to be able to detect stunting impacts of about 5pp or greater for the full 0–35‐month range (6pp for the 24–35 age group) and impacts on behavioural outcomes ranging between 2 and 9pp for the 0–11‐month cohort. These statistical power calculations used estimated means and intra‐cluster correlation coefficients from the baseline survey. The baseline sample size was lower; 3040 children were uniformly distributed over the 0–35‐month age range because we used it only to assess baseline equivalence and provide controls for the endline impact analysis.