CRITERIA OF VOCATIONAL SUCCESS 43
of them should not be combined or averaged. The series
of measures will have to be adjusted before averaging in
order to avoid giving undue weight to any one of the criteria.
The investigator may weight each of the contributing criteria
 in accordance with its importance as he judges it.
Statistical precautions to be borne in mind are discussed
in Chapter XVII.
A test may predict one sort of vocational accomplishment
 and not another. Hence, when more than one criterion
 is available, the better procedure is to correlate the
tests with each of the several criteria independently. If the
criteria are themselves not closely related, the probability of
finding a high correlation between a test and a criterion is
increased. If several criteria are used independently it will
be necessary to make for each of them a list of essential
abilities before constructing tests.
The care demanded in the choice of a criterion of success
is well demonstrated in Snow’s study of tests for the selection
 of taxicab chauffeurs (170). His problem was to cut
down the number of accidents by devising tests that would
predict relative freedom from accidents. So he turned to
the accident record for his criterion. He found that accidents
 could be classified according to the following types:
1. A type due to recklessness. (In this article we distinguish
between carelessness and recklessness. Carelessness is a general
word; it implies a lack of care for one reason or another, such as
driving without the brakes in proper condition. But recklessness
connotes a more or less deliberate lack of care. It is the type of
behavior for which we tend to say there is no excuse.) The reckless
 accident is one such as is caused by speeding, passing traffic
lights, or running on the left side of the street.
2. A type due to carelessness. This is one which results, for
example, when the driver goes out with a car which has a faulty
steering apparatus or too much play in the wheels. He does not
do so deliberately, but merely does not take the pains to learn the
condition of his car.
3. A type due to emotional instability. This is the type of
accident in which another car suddenly careens around the corner.
The driver could avoid an accident by immediately applying the

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