Note 2 — Chapter II

To make clear the way in which these figures are secured, and to show concretely what they mean, suppose that the twenty photographs are lettered A, B, C, D, etc. They are to be arranged in an order by each judge according to his judgment of the intelligence of the individuals, the individuals being unknown to the judges. Suppose that the ten judges place photograph A respectively in the following positions: 9, 11, 5, 8, 9, 12, 7, 8, 7, 14. The average of these ten positions is 9, which we then take as the standard or most probable position of photograph A. Only two of the judges actually place A in the ninth position. The other eight judges all vary more or less from this position. We then find how much each judge varies from the average of the group, and the ten variations are respectively 0, 2, 4, 1, 0, 3, 2, 1, 2, 5 positions. The average of these individual variations is 2.0 positions. This figure indicates how closely the ten judges agree in their estimates of photograph A, a small average deviation indicating close agreement. In this way we find for each of the twenty photographs its average deviation; and if the twenty figures thus secured are in their turn averaged we secure an approximate measure of the disagreement of the judges when estimating the intelligence suggested by the photographs. Similarly we may compute average deviations for any other trait which is judged. These final figures are the ones which are given in the table, each of them being the average of twenty photographs as judged by ten persons.