According to Pew Research Center surveys, 79% of U.S. adults were using the Internet in January 2011 and 83% were using it in January 2012 (USA TODAY, January 26, 2012). Suppose that these percentages are based on random samples of 1800 U.S. adults in January 2011 and 1900 in January 2012.
a. Let p1 and p2 be the proportions of all U.S. adults who were using the Internet in January 2011 and January 2012, respectively. Construct a 98% confidence interval for p1 – p2.
b. Using a 1% significance level, can you conclude that p1 is lower than p2? Use both the critical-value and the p-value approaches.