Question

determine the 99% confidence interval estimate for the population of a noaml distributed given

n= 81 s(d)= 104 x= 1,200

show formulas in excel

Answer 1

By Hand calculation:

Standard error = s(d) / = 104 / = 11.55556

z value for 99% confidence interval is 2.575829

Margin of error = Standard error * z

= 11.55556 * 2.575829

= 29.76515

99% confidence interval estimate

(Mean - Margin of error, Mean + Margin of error)

(1200 - 29.76515, 1200 + 29.76515)

(1170.235, 1229.765)

Using Excel, the margin of error is found by the below function,

=CONFIDENCE.NORM(0.01,104,81)

1st input is = 1 - Confidence level = 1 - 0.99 = 0.01

2nd input is s(d) (Standard deviation)

3rd input is sample size n.

So, 99% confidence interval estimate is Excel can be forund by below formula,

=1200 - CONFIDENCE.NORM(0.01,104,81)

and

=1200 + CONFIDENCE.NORM(0.01,104,81)