This report examines the possible bias in national estimates of standard Roll Back Malaria (RBM) indicators of insecticide-treated mosquito net (ITN) ownership and use. The analysis uses GPS data for 18 sub-Saharan African countries to correlate these measures with levels of malaria endemicity and seasonality and to recalculate coverage estimates based on the population at risk. The report proposes an approach to identifying populations at risk of malaria that countries could use to produce subnational estimates that account for variations in malaria endemicity or seasonality.