“1.11 Why Do Myths About Intelligence Definitions and Measurement Persist?
Given all this strong empirical evidence that intelligence test scores are meaningful, why does the myth persist that scores have little if any validity? Here is an informative example. From time to time, a college admissions representative will assert that in their institution they find no relationship between grade point average (GPA) and SAT scores. Such observations are virtually always based on a lack of understanding of a basic statistical principle regarding the correlation between two variables. To calculate a correlation between any two variables, there must be a wide range of scores for each variable. At a place like MIT, for example, most students fall in a narrow range of high SAT scores. This is a classic problem of restriction of range. There is little variance among the students, so in this case, the relationship between GPA and SAT scores will not be very strong. Sampling from just the high end or just the low end or just the middle of a distribution restricts range and results in spuriously low or zero correlations. Restriction of range actually accounts for many findings about what intelligence test scores “fail” to predict.”