To answer this question, we must first explain what IQ tests measure and then examine what an IQ score means.
Background
In 1955, American psychologist David Wechsler published a new intelligence test that became known as the Wechsler Adult Intelligence Scale (WAIS). He defined intelligence as “the global capacity of a person to act purposefully, to think rationally, and to deal effectively with his environment.” To measure this faculty, he created two sub-tests: one measuring “verbal intelligence” and the other, “non-verbal (performance) intelligence”.
Wechsler’s departure from a single measure of intelligence offered by the Stanford-Binet test evolved from his recognition that intelligence may have more than one dimension. Growing recognition of these multiple dimensions led to subsequent revisions of the Wechsler tests to include measures of verbal comprehension, perceptional reasoning, working memory, and processing speed. WAIS-IV, the fourth edition of the Wechsler tests, released by Pearson in 2008, has 10 subtests and 5 supplemental tests that summarize intelligence with two measures–a final IQ score and a General Ability Index, along with scores on the four dimensions described above It is the most widely-used test for adolescents and adults. The cognitive skills measured by the WAIS-IV is shown in the diagram below from Intelligence, IQ & Perception.
Meaning of an IQ Score
Assuming that intelligence is normally distributed, Wechsler mapped his test scale onto a normal distribution with mean 100 and standard deviation 15. By standardizing his tests in this way, Wechsler linked his scale directly to percentiles, allowing for immediate comparisons to average intelligence.
For example, the area of the shaded region left of IQ 115 is 84% (i.e., 50% + 34%) of the total area under the curve. So, someone with an IQ of 115 scored higher than 84% of the population and ranks in the 84th percentile. This is called the percentile ranking. Table 2–2 gives the percentiles that match familiar IQs.
Meaning of an IQ score
Your IQ score is a measure of the kinds of cognitive skills that are required in higher education and is therefore the best indicator of how easily you will learn academic subjects. However, it does not measure creativity, long-term problem solving, imagination or intellectual tenacity. Consequently it should not be interpreted as a complete measure of your intelligence. It’s the best measure of cognitive skills that we have (other than achievement) but it is limited in its prediction of your future success.
