The formula for sample size calculation for prevalence in community based studies is:

n = (z x z x p x q)/(dxd)

= (1.96)2(0.5)(0.5)/0. 12

= (3.84)(0.25)/0.01 = 96

Taking design effect =2, the total sample size becomes 96 x2 i.e. 192

For a 30 cluster technique, number of subjects to be selected per cluster = 192/30 = 6.4 (rounded up to 7)

That means we have to select 30 clusters, each with 7 units making a total sample size of 30 x 7 = 210 !!!

Interesting, isn't it ??

## Thursday, April 8, 2010

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