Developmental psychology.pdf

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Tests and Measurement 357
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Figure 13.11
Scattergram of Reliability. In this
test-retest reliability, the results of
two administrations of the same test
to the same subjects show a high
correlation.
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25 50 75 100 125 150
First test administration
Whenever a test is evaluated for reliability, the same procedures must be employed
on all occasions, and then the sets of scores are compared. The relationship
between each subject's scores, or each judge's scores, is expressed as a degree of correlation
or agreement (Figure 13.11).
Reliability Coefficients Perfect agreement is seldom found, but in general the more
extensive the test, the higher is the consistency. As more test items are included, the
less likely it is that the final score will be disrupted by one or two items that are
unsuccessful or misunderstood. However, as the time interval between testings increases,
reliability becomes lower, for the subjects' responses may be influenced by changes in
mood, setting, age, and cultural factors.
A numerical measure of a test's consistency, or reliability, is indicated by a
reliability coefficient, which may range from .00 to ± 1.00. A coefficient of zero means
that the test is completely unreliable, giving a totally unpredictable result on each occasion.
A coefficient of one is equally improbable, for it means that the test gives exactly
the same result every time it is administered to the same subject. Instead, a
worthwhile test is highly consistent but not perfect.
It is not uncommon to have reliability coefficients for mechanical aptitude in
the vicinity of .90. Coefficients for personality tests are lower because the results are
more likely to be influenced by temporary states, such as mood. Tests of perceptual
and motor skills for Air Force personnel have shown a range of reliability coefficients
from .64 to .95 (Hunter, 1975; Figure 13.12).
Test
Kinesthesis
Perceptual speed
Stress reactions
Associative learning
Memory
Concept identification
Divided attention
Coefficient
.93
.84
.92
.64
.95
.81
.95
Figure 13.12
Reliability Coefficients. These
coefficients indicate the reliability of a
series of tests of perceptual and
motor skills (Hunter, 1975).
Assessment of Validity
Perhaps Captain Holmgren, approaching some turbulence, has asked the passengers
to obey the no-smoking and seat-belt signs. In any case, we now encounter some special
difficulty ourselves, and it lies with the issue of validity. It is one thing for a test to be
reliable, giving the same result over and over again. It is another for the test to be
valid. A test that has validity measures the quality that it is intended to measure. It is
a potentially successful test. This issue of validity is the most crucial in the entire field
of psychological testing and the most difficult to assess satisfactorily.
A reliable test might or might not be valid, depending upon whether it measures
the intended trait. A test of running speed may give a highly reliable result, but
it is not a valid measure of flying ability. A test that has high validity, accurately measuring
flying ability, must be reliable, giving the same result from one time to the next,
unless the characteristic being measured itself changes. Certain flight-simulator tests,
for example, have been shown to have high validity as pilot-selection devices (Fowler,
1981).