Massive IQ gains in 14 nations: What IQ tests really measure.

Data from 14 nations reveal IQ gains ranging from 5 to 25 points in a single generation. Some of the largest gains occur on culturally reduced tests and tests of fluid intelligence. The Norwegian data show that a nation can make significant gains on a culturally reduced test while suffering losses on other tests. The Dutch data prove the existence of unknown environmental factors so potent that they account for 15 of the 20 points gained. The hypothesis that best fits the results is that IQ tests do not measure intelligence but rather a correlate with a weak causal link to intelligence. This hypothesis can also explain differential trends on various mental tests, such as the combination of IQ gains and Scholastic Aptitude Test losses in the United States. Over the last decade, scholars in many countries—largely unknown to one another—have been measuring IQ trends from one generation to the next. In this article their results are collected and analyzed so as to reap the benefits comparative data usually yield. It is also argued that this mass of data poses fundamental problems for developmental psychology, primarily concerning what factors have the most potent effect on IQ, what IQ tests measure, and how IQ tests should be used in making between-groups comparisons.