We will use a two-stage spatial sampling design for the main survey to measure outcomes on prevalence, coverage and morbidity.
Stage 1 sampling
We use a centric systematic area sampling approach using a non-overlapping hexagonal grid that divides the cluster into about 12 distinct sampling areas. In each of these hexagonal areas, sampling locations are selected from the nearest village / community / settlement from the centre of the hexagons. This stage 1 sampling plan is presented in Figure 1.
We will most likely choose 2 to 3 villages per hexagonal grid (for a total of 24 to 36 villages in total) so as to be able to achieve enough sample size for the PLW group. This is because we estimate there to be on any given day about 7 PLW in a village with a population of 200 persons in Sudan . This number of villages will most likely be enough as well to provide adequate number of MAM cases for the programme coverage indicator.
Stage 2 sampling
Because of the nature of the nested surveys, it would be most efficient that a full enumeration of children under 5 years and of PLW be done in each of the selected sampling villages in stage 1. This ensures that the sample sizes needed for the PLW and for programme coverage are reached. For large sampling locations (i.e., urban towns, large villages), a systematic sampling approach will be implemented to collect data on children under 5 for the prevalence, coverage and morbidity surveys. An active and adaptive case-finding approach will then be used to find all of the PLW in the sampling location.