Measuring treatment coverage for neglected tropical disease control programs: analysis of a survey design.

Monitoring of treatment coverage following mass drug administration is essential to ensure program success. Coverage results reported by drug administrators are often validated by using population surveys. This study evaluates the design of a multistage cluster sample survey conducted in 2007-2008 and implemented at the district level to assess drug coverage in the 4 African countries of Burkina Faso, Ghana, Niger, and Uganda. Estimates of precision of coverage were calculated, and factors contributing to the observed variance were analyzed. Precision of +/- 5 percentage points was obtained in 39% (n = 12) of cases, and precision of +/- 10 percentage points was obtained in 77% (n = 24) of cases. The factor having the largest impact on the actual precision obtained in these surveys was the high level of clustering, the impact of which is incorporated in the design effect. Key recommendations are made for the design and analysis of future surveys; guidelines are presented for thinking through the number of clusters that should be selected and how a cluster should be designed.