In: Statistics and Probability
. As health insurance costs and the number of disabled employees increase, more companies are firing these employees. A survey of 723 employers found that 195 dismiss employees as soon as they go on long-term disability.
a) = 195/723 = 0.2697
At 95% confidence interval the critical value is z* = 1.96
The 95% confidence interval for population proportion is
+/- z* * sqrt((1 - )/n)
= 0.2697 +/- 1.96 * sqrt(0.2697 * (1 - 0.2697)/723)
= 0.2697 +/- 0.0324
= 0.2373, 0.3021
b) At 99% confidence interval the critical value is z* = 2.58
The 95% confidence interval for population proportion is
+/- z* * sqrt((1 - )/n)
= 0.2697 +/- 2.58 * sqrt(0.2697 * (1 - 0.2697)/723)
= 0.2697 +/- 0.0426
= 0.2271, 0.3123
c) The 99% confidence interval is wider. Because if the confidence level increases, the margin of error also increases, so that the confidence interval becomes wider.