Intelligence: In Pursuit of Rational Thought and Effective Action 145
(a) Research has demonstrated that the IQ score is a variable.
(b) What are the two other names of the bell-shaped curve?
(c) What percent of subjects fall within an IQ range of 90 to 109, the Normal, or Average,
classification?
(d) What percent of subjects fall within an IQ score of 130 or above, the Very Superior clas-
sification?
Answers: (a) random; (b) The normal curve and the Gaussian curve; (c) 50 percent;
(d) 2.2 percent.
Validity and Reliability: Two Big Problems in Any Kind
of Testing
Let’s say that a confused auto mechanic gets certain important wires crossed on
the display panel in your car. You are driving merrily along and your gas gauge
reads “Full.” However, soon you are forced to pull over to the side of the road.
Your car has overheated and it’s also out of gas. What has gone wrong? The gas
gauge, unfortunately, was giving information on temperature, not fuel in the tank.
Under these conditions, the gas gauge had lost its validity as a measuring instru-
ment. Interestingly, it was functioning in a reliable manner. It was reliably giving
you the wrong information! As you can see, validity and reliability, although
related, are not the same thing.
Validity and reliability are important aspects of any kind of measurement and
testing. Intelligence tests are—like gauges, clocks, and rulers—measuring instru-
ments. Consequently, before they can be used to measure intelligence with any
degree of confidence, their validity and reliability must be assessed.
A valid testis one that measures what it is supposed to measure. If an intelli-
gence test really does in fact measure intelligence, then it is valid. But how can one
ascertain that the test is valid? Just because the questions in a test seemvalid does
IQ Categories
IQ Classification Percent
130 and above Very Superior 2.2
120–129 Superior 6.7
110–119 Bright Normal 16.1
90–109 Normal (or Average) 50.0
80–89 Dull Normal 16.1
70–79 Borderline 6.7
69 and below Cognitively Deficient 2.2
