Measures of Intelligence (continued)

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How to interpret an IQ score.

An IQ score represents how far the adolescent’s raw score (number of items answered correctly) differs from the typical performance of same-aged individuals. To develop the norms for the WISC-IV, thousands of children and adolescents were given the test; their performance created a bell-shaped curve.   The highest point of the curve represents the average performance of a particular age group and accounts for the scores of the largest number of adolescents. Adolescents who are represented to the right of the highest point answered more items correctly, and adolescents who are represented to the left of the highest point answered fewer items correctly. The bell-shaped, or normal, curve has at its center the mean, or average, score on this intelligence test (100) and a standard deviation of 15, which shows how spread out the scores are from the mean. also displays the intellectual labels that are applied to the various ranges of scores. An IQ of 100 can be interpreted to mean that an adolescent scored higher than 50% percent of adolescents who took this test and is in the “average” range.

The stability of IQ.

Stability refers to the consistency of performance over time. In other words, is an IQ score achieved at age 10 related to IQ at age 20? Research on the stability of IQ shows that the older the individual is at the first test-taking session, the better that score predicts IQ at later points in time. Correlations between IQ scores achieved after age 6 and those taken later are quite high (e.g., .70s–.80s). IQ scores obtained during preschool are less predictive of later scores (Humphreys & Davey, 1988). In addition, the less time between test-taking sessions produces stronger relationships between IQ scores. IQ tests taken several years apart yield IQ scores that are more similar than those from tests taken 20 years apart.