14.39 A newsletter rates mutual funds. Independent random samples of 12 funds with the highest rating and 12 funds with the lowest rating were chosen. The following figures are percentage rates of return achieved by these 24 funds in the next year.

Highest rated 8.8 10.8 8.4 9.0 5.4 5.0 6.8 11.2 8.2 7.4 4.6 6.0 Lowest rated 4.6 2.7 2.5 1.7 4.0 1.4 4.0 1.7 2.0 2.8 1.2 4.0 Test at the 1% level the null hypothesis of no difference between the central locations of the population distributions of rates of return against the alternative that the highestrated funds tended to achieve higher rates of return than the lowest-rated funds.