21.25 68% confidence. We used the 95 part of the 68–95–99.7 rule to give a recipe for a 95% confidence interval for a population proportion p.
(a) Use the 68 part of the rule to give a recipe for a 68% confidence interval.
(b) Explain in simple language what “68% confidence’’ means.
(c) Use the result of the Gallup Poll (Example 3, page 499) to give a 68% confidence interval for the proportion of adult Americans who reported actively trying to avoid drinking regular soda or pop in 2015. How does your interval compare with the 95% interval in Example 3?