Question

A Gallup Poll of American adults in February 2009 asked the following question. “Which of the following presidents would you regard as the greatest: Washington, Franklin Roosevelt, Lincoln, Kennedy, or Reagan?” The order of the presidents was rotated to avoid bias. Based on the sample, a 95% confidence interval for the actual proportion American adults who choose Lincoln as the greatest is given by (0.1505, 0.2214).

What is the margin of error? Give the exact answer as a decimal.

Answer 1

Solution :

A 95% confidence interval = (0.1505, 0.2214)

Point estimate = = (Lower confidence interval + Upper confidence interval ) / 2

Point estimate = = (0.1505 + 0.2214) / 2

Point estimate = = 0.1859

Margin of error = E = Upper confidence interval -

Margin of error = E = 0.2214 - 0.1859

Margin of error = E = 0.0355