COM3710 - Section 1 - Homework 4




riosjosh
Homework 4 (10 points possible, Due 10-27) Comm 3710
Standard Error of Percentage Hand-Calculations

  1. In a recent survey of PR firms in Salt Lake City, 57 out of 100 firms reported a preference for hiring communication graduates from the University of Utah over graduates of the program down south. Calculate the margin of error (confidence interval) for this polling result at the 95% confidence level. Circle your answer.

Standard Error of Percentage = Ö((P*Q)/N)
P = 57/100 = 0.57
Q = 1 – 0.57 = 0.43
N = 100

s = Ö((P*Q)/N) = Ö((.57*.43)/100) = Ö((0.25)/100) = Ö(0.0025) = 0.05 or 5%

95% confidence level = ± 10

The margin of error at the 95% confidence level then is 47-67, which is two standard errors away from the population parameter.

  1. In a recent survey of 1000 undergraduate business students, asking whether the August 2011 downgrading of the United States credit rating was a significant impediment to the economy, 340 students said they “strongly disagreed,” and 660 said they “strongly agreed”. Calculate the margin of error (confidence interval) for this polling result at the 95% confidence level. Circle your answer.

Standard Error of Percentage = Ö((P*Q)/N)
P = 340/1000 = 0.34
Q = 1 – 0.34 = 0.66
N = 1000

s = Ö((P*Q)/N) = Ö((.34*.66)/1000) = Ö((0.22)/1000) = Ö(0.00022) = 0.01 or 1%

95% confidence level = ± 2

The margin of error at the 95% confidence level for those who “strongly disagree” then is 32-36, which is two standard errors away from the population parameter.

The margin of error at the 95% confidence level for those who “strongly agree” then is 64-68, which is two standard errors away from the population parameter.