Refer to the U.S. Army Corps of Engineers study of contaminated fish in the Tennessee River. The Corps of Engineers has collected data for a random sample of 144 fish contaminated with DDT. (The engineers made sure to capture contaminated fish in several different randomly selected streams and tributaries of the river.) The fish weights (in grams) are saved in the DDT file. The Army Corps of Engineers wants to estimate the true variation in fish weights to determine whether the fish are stable enough to allow further testing for DDT contamination.

a. Use the sample data to find a 95% confidence interval for the parameter of interest.

b. Determine whether the confidence interval, part a, is valid.