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7.5 Average ARTI in India


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 19 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. 

The estimates of prevalence of infection from the rural areas of four zones were pooled together to obtain a national level estimate for rural areas, as under:  


where
P is the prevalence at national level, pi is the estimated prevalence for
the ith zone and wi is
the corresponding weight – proportion of the rural population in the ith
zone out of the total rural
population in the country. The Standard Error (S) was estimated as under: 



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 cutoff point method (Method I) as well as by mirrorimage
technique (Method II). The resultant national estimates are as under: 


