ck 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

One other point: If one or more tests of a year group have been omitted,
as sometimes happens either from oversight or lack of time, the question
arises how the tests which were given in such a year group should be
evaluated. Suppose, for example, a subject has been given only four of
the six tests in a given year, and that he passes two, or half of those
given. In such a case the probability would be that had all six tests
been given, three would have been passed; that is, one half of all.
It is evident, therefore, that when a test has been omitted, a
proportiona