Question

A study with 100 observations gave a mean of 70. Assume that the normal standard deviation is 15. Plot the 90%, 95%, and 99% confidence intervals above the line and comment on the effect of the confidence level on the width of the interval.

Answer 1

a) For 90% confidence, z = 1.645

Hence,

90% confidence interval will be:

(67.53, 72.47)

b) For 95% confidence, z = 1.96

Hence,

95% confidence interval will be:

(67.06, 72.94)

c) For 99% confidence, z = 2.576

Hence,

99% confidence interval will be:

(66.14, 73.86)

d) As we increase the confidence level, the width of confidence interval increases.