PSYCHOLOGICAL TESTS ;
as it is supposed to compensate for the effect of guessing.
If a person goes through the test and indicates his answers
at random, or by guessing, about half of the answers will
be correct. If the number wrong is subtracted from the
number right, his score will be zero. Those solutions which
represent mere guesses cancel each other. In theory this
method of scoring eliminates the factor of guesswork. It
is true that by guessing, a score of zero on this basis will
be more probable than any other score, but the majority of
scores obtained by guesswork will not be zero, just as in a
normal distribution curve although the modal score is the
most probable score, most persons do not make this score.
The chief recourse is to increase the number of items. The
greater the number of items in a two-choice test, the more
restricted the range of scores that can be obtained purely by
guessing as compared with scores representing knowledge.
Several experimental studies of this method of scoring
have been made. Ruch and Stoddard (15 5) and Paterson
and Langlie (131) both discovered that the R-W method of
scoring was less reliable than R alone. Wood (223) found
that the validity of R-W was greater than R alone in four
out of five examinations when the number of items in the
examination was above fifty.
Thurstone gives an exact method of arriving at a proper
weighting of right and wrong answers. (See page 187.)
Another method of scoring is the difference between true
values and guesses or estimates which the subject is required
 to make.
The number of times a standardized prompting must be
given in order to make the individual carry on the task to
its successful completion has been used.
Various ratios may be treated as scores, such as the ratio
of an estimate to the true value, the ratio of one score to
another, or the ratio of scores in one part of a test to scores
in another part.

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