A First Course in Statistics, 12th Edition

5.6 Confidence Interval for a Population Variance (Optional)

In the previous sections, we considered interval estimation for population means or proportions. In this optional section, we discuss a confidence interval for a population variance, ${\sigma }^2$.

Recall Example 1.4 (p. 10) and the Consider a U.S. Army Corps of Engineers study of contaminated fish in the Tennessee River, Alabama. It is important for the Corps of Engineers to know how stable the weights of the contaminated fish are. That is, how large is the variation in the fish weights? The keyword “variation” indicates that the target population parameter is ${\sigma }^2$, the variance of the weights of all contaminated fish inhabiting the Tennessee River. Of course, the exact value of ${\sigma }^2$ will be ...