The only objection to this method is that it requires a great many experiments in order to get an average result.

To be reliable, an average must be secured, seeing that, for one or two or a few trials, the student may guess right without remembering the original square at all.

By taking a large number of persons, such as the three hundred students, this objection may be overcome.

Comparing the averages, for example, of the results given by the men and women respectively, we found practically no difference between them.
This last point may serve to introduce a distinction which is important in all work in experimental psychology, and one which is recognised also in many other sciences--the distinction between results obtained respectively from one individual and from many.

Very often the only way to learn truth about a single individual is to investigate a number together.