Are based on a report of a Field poll printed in the Sacramento Bee on July 7, 2000 (Dan Smith, p. A4), with the headline, "Ratings Up for Boxer, Feinstein in New Poll." The results were reported with a graphical display containing the information that "results are based on a statewide survey of 750 adults conducted June 9-18. The sample includes 642 voters considered likely to vote in the Nov. 7 general election. The margin of error is 3.8 percentage points."
The report stated that the margin of error was 3.8 percentage points. This value is based on the 642 voters who were considered likely to vote and uses the precise formula you will learn in Chapter 10.
a. Compute the conservative margin of error for this poll based on those likely to vote, and compare it to the precise margin of error presented.
b. For this sample, 57% reported that they approve of Dianne Feinstein's job performance. What is an approximate 95% confidence interval for the percent of all likely voters who approve of her performance?