In: Statistics and Probability
In a school district, all sixth grade students take the same standardized test. The superintendant of the school district takes a random sample of 22 scores from all of the students who took the test. She sees that the mean score is 160 with a standard deviation of 28.2396. The superintendant wants to know if the standard deviation has changed this year. Previously, the population standard deviation was 28. Is there evidence that the standard deviation of test scores has increased at the α=0.005 level? Assume the population is normally distributed. Step 2 of 5 : Determine the critical value(s) of the test statistic. If the test is two-tailed, separate the values with a comma. Round your answer to three decimal places.