Minimum detectable effect size for main outcomes (accounting for sample
design and clustering)
We base our power calculations on five measures: household food consumption scores (FCS, mean 45.5 and standard deviation 17.39), household food expenditures (mean 8.46 and standard deviation 9.55), an indicator for whether the household is worried about lack of food (mean 0.61 and standard deviation 0.49), weight-for-age (mean -1.43 and standard deviation 1.64), and height-for-age (mean -0.64 and standard deviation 1.22). Assuming 44 schools per treatment arm, 20 children per school, one follow-up
observation, and power of the test of 80%, yields a minimum detectable effect (MDE) of 0.19 standard deviations for FCS, food expenditures, weight-for-age, and height-for-age, and of 0.20 standard deviations for the worry indicator. With two follow-up measurements
and assuming a correlation of 0.2 between follow-up measurements, our experiment is powered to detect an effect of 0.14 standard deviations for FCS and food expenditures, 0.15 for weight-for-age and height-for-age, and 0.16 for the worry indicator. Increasing
the correlation between follow up rounds to 0.5 yields an MDE of 0.16 for all indicators excluding weight-for-age, whose MDE is 0.17 standard deviations.
Household FCS, food expenditure, and the worry indicator come from the 2015-2016 wave of the Malawi Living Standard Measurement Survey (LSMS). Weight-for-age and height-for-age data come from the 2019 wave of the Malawi Demographic and Health survey (DHS).