4. Unbiased Estimators What is an unbiased estimator? Is the sample variance an unbiased estimator of the population variance? Is the sample standard deviation an unbiased estimator of the population standard deviation?

Finding Critical Values. In Exercise 5–8, find the critical values and that correspond to the given confidence level and sample size.

5. 95%; n 5 27 6. 95%; n 5 7 7. 99%; n 5 41 8. 90%; n 5 91 Finding Confidence Intervals. In Exercises 9–12, use the given confidence level and sample data to find a confidence interval for the population standard deviation In each case, assume that a simple random sample has been selected from a population that has a normal distribution.