Question: One reads that a business school graduate with an undergraduate degree earns more than a high school graduate with no additional education, and a person with a master’s degree or a doctorate earns even more. To investigate we select a sample of 25 mid-level managers of companies with less than 200 employees. Their incomes, classified by highest level of education, follow.

Test at the .05 level of significance that there is no difference in the arithmetic mean salaries of the three groups. If the null hypothesis is rejected, conduct further tests to determine which groups differ.