P = P1 + Po = 0.83 + 0.64 = 0.72 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(0.72)(1-0.72) + 0.84√0.83(1-0.84) + 0.60(1-0.60))2 (0.75 - 0.50 )2 n = 54 Therefore sample size = 108 + 20 % drop out = 130 By using PS software - sample size : 130