1. Testing and Estimating a Single Variance or Standard Deviation
Section 3
Testing and Estimating a Single Variance or Standard Deviation

2. Formulas
df = n – 1

3. Example
A store has been using the independent lines procedure to check out customers and found that the standard deviation of the waiting times is 7 minutes. When the single line procedure was introduced, the standard deviation of the waiting times of 25 customers was found to be 4 minutes. Use a 5% level of significance to test the claim that the variance of waiting times has been reduced.

4. Hypotheses
Ho: = 49
H1: < 49

5. Confidence Interval for
= critical value using df = n – 1 and = (1 – c)/2
= critical value using df = n – 1and = (1 + c)/2

6. Example
A random sample of 30 plants has a sample standard deviation of 3.4 days for maturity. Find a 95% confidence interval for the population variance.