Fig 1. Survey timeline, sampling strategy, data collection methods and outcomes measured for the 2012 survey of the impact evaluation of Zimbabwe’s Accelerated PMTCT program.

* In each catchment area, we used one of the following sampling fractions (so that we enroll an average of 50 mother-infant pairs per catchment area, which was one of the assumptions of our power calculations): 1) 1 in 4 eligible mother-infant pairs if the catchment area had over 300 eligible infants, 2) 1 in 2 infants if the catchment area had 150 to 300 eligible infants, or 3) all the mother-infant pairs if the catchment area had fewer than 150 eligible infants.