Use the expression in the accompanying discussion of sample size to find the size of each sample if you want to estimate the difference between proportions of men and women who own smartphones. Assume that you want 90% condence that your error is no more than 0.04. 0 Click the icon to view the discussion of sample size. The sample should include :| men and :| women. (Type whole numbers.) Sample size discussion The sample size needed to estimate the difference between two population proportions to within a margin of error E with a condence level of 1 - or can be found by using the following expression: Replace n1 and n2 by n in the preceding formula (assuming that both samples have the same size) and replace each of p1 , q1, p2, and :12 by 0.5 (because their values are not known). Solving for n results in this expression: 2 za/Z n= 2 2E