Two USA TODAY/Gallup polls of 979 U.S. adults each, one in November 2001 and the other in March 2009, asked “Did the United States make a mistake in sending military forces to Afghanistan?” The numbers of affirmative responses in the two polls were 90 and 418, respectively. Determine a 95% confidence interval for the difference between the percentages of all U.S. adults who, during the two time periods, thought sending military forces to Afghanistan was a mistake.
The two-proportions plus-four z-interval procedure as discussed on page 467 to find the required confidence interval. Interpret your results.