e, for the question is one which
should be understood. Besides, explanations and coaxing are too often
equivalent to answering the question for the child. It is almost
impossible to impress this danger sufficiently upon the untrained
examiner. One who is not familiar with the psychology of suggestion may
put the answer in the child's mouth without suspecting what he is doing.

ADHERING TO FORMULA. It cannot be too strongly emphasized that unless we
follow a standardized procedure the tests lose their significance. The
danger is chiefly that of unintentionally and unconsciously introducing
variations which will affect the meaning of the test. One who has not
had a thorough training in the methods of mental testing cannot
appreciate how numerous are the opportunities for the unconscious
transformation of a test. Many of these are pointed out in the
description of the individual tests, but it would be folly to undertake
to warn the experimenter against every possible error of this kind.
Sometimes the omission or the addition of a single phrase in giving
the test will alter materially the significance of the response.
Only the trained psychologist can vary the formula without risk of
invalidating the result, and even he must be on his guard. All sorts of
misunderstandings regarding the correct placing of tests and regarding
their accuracy or inaccuracy have come about through the failure of
different investigators to follow the same procedure.

One who would use the tests for any serious purpose, therefore,
must study the procedure for each and every test until he knows it
thoroughly. After that a considerable amount of practice is necessary
before one learns to avoid slips. During the early stages of practice it
is necessary to refer to the printed instructions frequently in order to
check up errors before they have become habitual.

The instructions hitherto available are at fault in not defining the
procedure with sufficient definiteness, and it is the purpose of this
volume to make good this deficiency as far as possible.

It is too much, however, to suppose that the instructions can be made
"fool-proof." With whatever definiteness they may be set forth,
situations are sure to arise which the examiner cannot be formally
prepared for. There is no limit to the multitude of misunderstandings
possible. After testing hundreds of children one still finds new
examples of misapprehension. In a few such cases the instruction