Question

Mean of 0.52

Standard deviation of 0.50

Sample size is 25

80% confidence interval is (0.39 to 0.65)

95% confidence interval is (0.32 to 0.72)

How did they get this? Please help!

Answer 1

Confidence interval, CI = Z*

Here, = 0.52

= 0.50

n = 25

For 80% confidence level, Z* = 1.28

80% confidence interval = 0.52 1.28x

= 0.52 0.13

= (0.39 to 0.65)

For 95% confidence level, Z* = 1.96

80% confidence interval = 0.52 1.96x

= 0.52 0.20

= (0.32 to 0.72)