The Emerging Workforce Study conducted by Harris Interactive on behalf of Spherion, a leader in providing value-added staffing, recruiting, and workforce solutions, utilized a random sample of 502 senior human resources executives. The survey asked which methods the executives felt led them to find their best candidates. The file titled Referrals contains the responses indicating those that chose "referrals" as their best method.
a. Determine the margin of error that would accrue with a confidence level of 95%.
b. Calculate a 95% confidence interval for the proportion of executives who chose "referrals" as their best method.
c. Determine the sample size required to decrease the margin of error by 25%.