Refer to the Applied Psychology in Criminal Justice (Sept. 2009) study of the personality characteristics of convicted drug dealers, Exercise. A random sample of 100 drug dealers had a mean Wanting Recognition (WR) score of 39 points, with a standard deviation of 6 points. The researchers also are interested in σ2, the variation in WR scores for all convicted drug dealers.
a. Identify the target parameter, in symbols and words.
b. Compute a 99% confidence interval for σ2.
c. What does it mean to say that the target parameter lies within the interval with “99% confidence”?
d. What assumption about the data must be satisfied in order for the confidence interval to be valid?
e. To obtain a practical interpretation of the interval, part b, explain why a confidence interval for the standard deviation, σ, is desired.
f. Use the results, part b, to compute a 99% confidence interval for σ. Give a practical interpretation of the interval.