21. Ranking the Presidents. A study asked a randomly selected group of liberal historians and a randomly selected group of conservative historians to rank the presidents of the United States since George Washington.¹² Interestingly, both groups agreed on the top five presidents, but the rankings were not exactly the same. The rankings for the top five are shown here. Test whether a rank correlation exists between the liberal ranks and the conservative ranks, using level of significance . Note that you need not calculate the ranks, as the ranks are given.