Question

A sample of 169 observations showed an average of 15 and a standard deviation of 26. Construct the 88% confidence interval for the population mean. What is the upper limit of this interval

Answer 1

18.11

Explanation:

The formula for Confidence Interval is given as:

Confidence Interval = μ ± z × σ /√n

μ = the population mean/average = 15

σ = the population standard deviation = 26

z = z score of 88% confidence interval = 1.5548

= 15 ± 1.5548× 26/√169

= 15 ± 1.5548 × 26/13

= 15 ± 1.5548 × 2

= 15 ± 3.11

Hence,

Confidence Interval = 15 ± 3.11

Lower Limit

= 15 - 3.11

= 11.89

Upper limit

= 15 + 3.11

= 18.11

Therefore, the upper limit of the 88% confidence interval is 18.11