As stated in the preceding pages, the country was divided into four exclusive and exhaustive zones for the purpose of the survey, each having approximately the same population. The survey in each zone was conducted independently keeping the methodology same in all the zones. The sampling methodology as well as the sample size within each zone was decided with the objective of providing an independent estimate of prevalance of infection among children 1-9 years of age for each zone with the corresponding standard error. The estimation of prevalance of infection to compute ARTI at the national level is a post survey exercise and hence may have its inherent limitations. The national estimate of prevalance has to be obtained by pooling the zonal estimates by providing appropriate weights. In this context, the sampling methodology adopted for the survey on the whole approximates to a stratified sampling strategy. The four zones of the country, considered as the strata, together constitute the nation and the zones have been so formed that each one constitute a compact stratum.

where si is the standard error for the ith zone.

The prevalence of infection with standard error in urban areas of the four zones were also estimated in the same manner.

 The rural and urban estimates of prevalence of infection at the national level were similarly pooled to obtain the overall national estimate.

The estimates were carried out as above, by pooling the zonal level estimates that were obtained by cut-off point method (Method I) as well as by mirror-image technique (Method II). The resultant national estimates are as under:

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