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.

High School Undergraduate Master’s Degree or Less Degree or More 45 49 51 47 57 73 53 85 82 62 73 59 39 81 94 43 84 89 54 89 89 92 95 62 73

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.