Statistical inference of risk difference in K correlated 2 x 2 tables with structural zero

K correlated 2 x 2 tables with structural zero are commonly encountered in infectious disease studies. A hypothesis test for risk difference is considered in K independent 2 x 2 tables with structural zero in this paper. Score statistic, likelihood ratio statistic and Wald-type statistic are proposed to test the hypothesis on the basis of stratified data and pooled data. Sample size formulae are derived for controlling a pre-specified power or a pre-determined confidence interval width. Our empirical results show that score statistic and likelihood ratio statistic behave better than Wald-type statistic in terms of type I error rate and coverage probability, sample sizes based on stratified test are smaller than those based on the pooled test in the same design. A real example is used to illustrate the proposed methodologies.