How's the economy? A pollster wants to construct a 95% confidence interval for the proportion of adults who believe that economic conditions are getting better. Part: 0 / 2 Part 1 of 2 (a) A poll taken in July 2010 estimates this proportion to be 0.39. Using this estimate, what sample size is needed so that the confidence interval will have a margin of error of 0.03? A sample of adults is needed to obtain a 95% confidence interval with a margin of error of 0.03