In: Statistics and Probability
A recent survey showed that 65% of U.S. employers were likely to require higher employee contributions for health care coverage. Suppose the survey was based on a sample of 600 companies. Find the 98% confidence interval for the proportion of all companies likely to require higher employee contributions for health care coverage.
Find left endpoint and right endpoint.
Solution :
Given that,
n = 600
Point estimate = sample proportion = = 0.65
1 - = 1 - 0.65 = 0.35
At 98% confidence level the z is ,
= 1 - 98% = 1 - 0.98 = 0.02
/ 2 = 0.02 / 2 = 0.01
Z/2 = Z 0.01 = 2.326
Margin of error = E = Z / 2 * (( * (1 - )) / n)
= 1.96 * (((0.65 * 0.35) / 600)
= 0.045
A 98% confidence interval for population proportion p is ,
- E < p < + E
0.65 - 0045 < p < 0.65 + 0.045
0.605 < p < 0.695
Left endpoint = 0.605
right endpoint = 0.695