Question

We wish to create a 90% confidence interval for the Variance given that a sample of 30 has a standard deviation of 2. Find the Lower value for the confidence interval.Round to tenths.

Answer 1

Given that, sample size (n) = 30

sample standard deviation (s) = 2

confidence level = c = 0.90

=> significance level = 1 - c = 1 - 0.90 = 0.10

Degrees of freedom = n - 1 = 30 - 1 = 29

Using Excel we get, chi-square critical value as follows:

The 90% confidence interval for population variance is,

Where,

Upper value for the confidence interval is 2.7

Lower value for the confidence interval is 6.6