Page:Popular Science Monthly Volume 63.djvu/164

160 do graduate. It is evident that a few students graduating in a class above forty years of age—by no means an unheard-of state of affairs—would unfairly raise the average age of that class, since it is manifestly impossible to graduate twenty years below the normal age. Again, a class, or series of classes, may graduate a considerable number of its members below twenty, while a still larger number graduates above twenty-four or twenty-five. The curve of distribution of the ages of graduation will then resemble the letter M. Manifestly, in such a case, which occurs several times, the arithmetical average tells us nothing of value. Finally, the median age gives us the exact information that one half the students in question graduated at or above the given age, and the other half at or below it. The curves of distribution, moreover, given in the plates for all graduates and all colleges for the years 1850-59 and 1890-99, show exactly what percentage graduated at each age.

We now come to a consideration of Table I. The most obvious and surprising thing that strikes us at first sight is the fact that our