become acquainted with some of the tests. In such cases it is a
great convenience to have a few substitutes available.

It is necessary, however, to warn against a possible misuse of
alternative tests. _It is not permissible to count success in an
alternative test as offsetting failure in a regular test._ This would
give the subject too much leeway of failure. There are very exceptional
cases, however, when it is legitimate to break this rule; namely, when
one of the regular tests would be obviously unfair to the subject being
tested. In year X, for example, one of the three alternative tests
should be substituted for the reading test (X, 4) in case we are testing
a subject who has not had the equivalent of at least two years of
school work. In year VIII, it would be permissible to substitute the
alternative test of naming six coins, instead of the vocabulary test, in
the case of a subject who came from a home where English was not spoken.
In VII, it would perhaps not be unfair to substitute the alternative
test, in place of the test of copying a diamond, in the case of a
subject who, because of timidity or embarrassment, refused to attempt
the diamond. But it would be going entirely too far to substitute an
alternative test in the place of every regular test which the subject
responded to by silence. In the large majority of cases persistent
silence deserves to be scored failure.

Certain tests have been made alternatives because of their inferior
value, some because the presence of other tests of similar nature in the
same year rendered them less necessary.

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 ba