3. Pregnancy rate between letrozole and CC From Mosammat Rashida Begum 2008 Letrozole 2.5mg - pregnancy rate - 40.6% CC 100mg - pregnancy rate - 18.7% ( Po ) = 0.18 (P1) = 0.41 P = P1 + Po = 0.41 + 0.18 = 0.30 zα = 1.96 zβ = 0.84 for 80% power 2 2 Significance level (α) = 5% (0.05) Power of study ( 1 - β )= 80% β =20% ( 0.2 ) n = (zα√2P(1-P) + zβ√P1(1-P1)+Po(1-Po))2 (P1-Po)2 n = ( 1.96√2(0.30)(1-0.30) + 0.84√0.41(1-0.41) + 0.18(1-0.18))2 (0.41-0.18 )2 n = 61 Therefore sample size = 120 + 20 % drop out n= 146