FINDING MENTAL AGE. As there are six tests in each age group from III to X, each test in this part of the scale counts 2 months toward mental age. There are eight tests in group XII, which, because of the omission of the 11-year group, have a combined value of 24 months, or 3 months each. Similarly, each of the six tests in XIV has a value of 4 months (24 ÷ 6 = 4). The tests of the "average adult" group are given a value of 5 months each, and those of the "superior adult" group a value of 6 months each. These values are in a sense arbitrary, but they are justified in the fact that they are such as to cause ordinary adults to test at the "average adult" level. The calculation of mental age is therefore simplicity itself. The rule is: (1) Credit the subject with all the tests below the point where the examination begins (remembering that the examination goes back until a year group has been found in which all the tests are passed); and (2) add to this basal credit 2 months for each test passed successfully up to and including year X, 3 months for each test passed in XII, 4 months for each test passed in XIV, 5 months for each success in "average adult," and 6 months for each success in "superior adult." For example, let us suppose that a child passes all the tests in VI, five of the six tests in VII, three in VIII, two in IX, and one in X. The total credit earned is as follows:-- _Years__Months_ Credit presupposed, years I to V 5 Credit earned in VI, 6 tests passed, 2 months each 1 Credit earned in VII, 5 tests passed, 2 months each 10 Credit earned in VIII, 3 tests passed, 2 months each 6 Credit earned in IX, 2 tests passed, 2 months each 4 Credit earned in X, 1 test passed, 2 months 2 ---- ---- Total credit 7 10 Taking a subject who tests higher, let us suppose the following tests are passed: All in X, six of the eight in XII, two of the six in XIV, and one of the six in "average adult." The total credit is as follows:-- _Years__Months_ Credit presupposed, years I to IX 9 Credit earned in X, 6 tests passed, 2 months each 1 Credit earned in XII, 6 tests passed, 3 months each 1 6 Credit earned in XIV, 2 tests passed, 4 months each 0 8 Credit earned in "average adult," 1 success, 5 months 5 ---- ---- Total credit 12 7