An automobile manufacturer employs sales representatives who make calls on dealers. The manufacturer wishes to compare the effectiveness of four different call-frequency plans for the sales representatives. Thirty-two representatives are chosen at random from the sales force and randomly assigned to the four call plans (eight per plan). The representatives follow their plans for six months, and their sales for the six-month study period are recorded. These data are given in the file P09_53.xlsx.
a. Do the sample data support the hypothesis that at least one of the call plans helps produce a higher average level of sales than some other call plan? Perform an appropriate statistical test and report a p-value.
b. If the sample data indicate the existence of mean sales differences across the call plans, which plans appear to produce different average sales levels? Use 95% confidence levels for the differences between all pairs of means to answer this question.