Error in IQ Test Scores
By Inderbir Kaur Sandhu, Ph.D
Q:
Our daughter took the WPPSI at age 4 years and 6 mos. She is
now 9 years 5 months. What is the % of error in the test
scores? Does an individual IQ score change? Why do school
districts not recognize IQ as an appropriate measure of
giftedness? Any information would be helpful.
A: Usually, the percentage of
error in standardized tests is taken into account in the
percentile band. The error of measurement here refers to the
amount by which the score that is actually observed differs
from a hypothetical true score. A standard error of
measurement is the amount an observed score that is expected
to fluctuate around the true score. For example, the
obtained score will not differ by more than plus or minus
one standard error from the true score about 68% of the
time. For about 95% of the time, the obtained score will
differ by less than plus or minus two standard errors from
the true score.
A score without error is a true score, which is entirely
free of error; a hypothetical value that can never be
obtained by testing, since a test score always involves some
measurement error. A true score may be thought of as the
average of an infinite number of measurements from the same
or exactly equivalent tests, assuming no practice effect or
change in the person taking the test during the testing. The
standard deviation of this infinite number of scores is
known as the standard error of measurement.
Gifted programs in schools usually have their own measures
in determining students who will benefit most from such
programs. Achievement tests are perhaps more reliable in
screening students for such programs. Some students may have
very high IQ, but the gifted program may not suit them very
well. My feel is that school districts need to practice some
kind of standardization in screening children for gifted
programs; hence only results/scores from certain tests taken
in certain centers may be accepted. In your daughter's case,
the test has been taken five years ago; hence there may be a
slight change in IQ on a revised version. It is best to take
another standardized IQ test if you need to place her in
certain programs. You should also speak to the school
authorities as they may be the best source for information
in this case.
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