The prevalence of asthma was found to be 6.6 % and the difference of asthma prevalence between the urban centers was statistically non-significant (p = 0.059).

Inverse Gaussian distribution, Sequential test, Group sequential test,

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No abstract

Group sequential designs are widely used in Phase II clinical trials, which are usually undertaken to evaluate the response probability of specific treatment regimen. In most randomized clinical trials with sequential patient entry, fixed sample size design is unjustified on ethical grounds and sequential designs are often impractical. However group sequential designs are generally more practical and they provide much of the saving possible from sequential designs. Optimal restricted two-stage design is the simplest form of a group sequential design. In this study, group sequential design obtained by () t * α functions characterized using the type-I error probability and optimal restricted two stage design has been compared for the cases that the group sizes are equal. Furthermore, their efficiency regarding fixed sample size design has been calculated and the results have been discussed.