Sep 10, 2025·Advanced Topics & ResearchFlynn Effect
Explore the Flynn effect, the rise of IQ scores in the 20th century, misconceptions about its meaning, and the recent reverse trends seen in some countries.
Dr. Russell T. WarneChief Scientist
One of the most fascinating concepts in intelligence research is the Flynn effect. This is the tendency throughout the 20th century for average IQ test performance to improve over time. Philosopher James Flynn published two articles in the 1980s documenting this trend, first in the United States, and later in 13 additional industrialized countries. The increase was substantial: an average of 3 points per decade. This means that every generation, IQ would rise about 15 points. If taken at face value, the implications were hard to believe: the average person from your grandparents’ generation would be as intelligent as someone in the bottom 2% of intelligence today (around the cutoff for an intellectual disability). Projecting back even further, Flynn’s findings implied that the average person 100 years earlier would be unable to learn language or go to the bathroom by themself. Clearly this couldn’t be true. What was going on???
Understanding the Flynn effect
There are a lot of misconceptions about the Flynn effect. So, before explaining it further, it is important to correct common misunderstandings. First, James Flynn did not discover the Flynn effect, nor did he ever claim to. It was first noticed in the 1930s, long before Flynn started his career. He certainly popularized it, but psychologists studying IQ at the time were aware of the phenomenon of increasing performance on IQ tests. The most well known example of the pre-Flynn Flynn effect was the higher performance on IQ tests in World War II, compared to World War I soldiers. Second, Flynn did not name the Flynn effect after himself. Richard Herrnstein and Charles Murray gave it that name in their bestseller book The Bell Curve. Third, the Flynn effect does represent a real increase in intelligence. It can’t because of the level of disability in the past that it would imply. But it does reflect an increase in IQ test performance. That’s not the same thing as intelligence. Some people (including Flynn originally, though he changed his mind later) believe that this proves that IQ tests don’t really measure intelligence. That is not correct. IQ measures a mixture of g (which many scientists consider to be the same as general intelligence) and non-g cognitive abilities. The Flynn effect operates on the non-g contributions to IQ. These range from mundane contributions, like increased guessing on IQ tests, to important causes of higher performance, such as higher levels of education and literacy. Fourth, the changes to the non-g contributions to IQ mean that IQ scores cannot be compared across different time periods. This explains the paradox that Flynn pointed out: the IQ tests were supposed to measure intelligence, but that interpretation breaks down when comparing historical scores to current ones. The changes in performance on the non-g abilities over time meant that earlier and later scores weren’t measuring the same mix of cognitive abilities -- but scores from different people taking an IQ test at the same time don’t have this problem. That means it makes sense to say that Examinee A is smarter than Examinee B when both took the same IQ test in the same year. But if Examinee A took the test this year and Examinee B took the test 30 years ago, then it is not justifiable to say that Examinee A is smarter than Examinee B. Now, about 40 years after Flynn first brought attention to the phenomenon, it is clear that the Flynn effect is caused by changes to the non-g abilities that the environment emphasizes. Sometimes, this is due to changes in the school curriculum, and sometimes it is not. As tests measure tasks that people have improved over time, then the overall IQ will increase without the core intelligence level changing at all. In essence, society -- whether intentionally or not -- trained people to perform in the tasks and abilities that the IQ tests measure.
Reverse Flynn effect?
Some countries, including Germany, France, and Norway, have seen a decline in IQ scores in the 21st century. This has led some people to worry that intelligence in these countries is decreasing and that it might decrease in other countries. These fears are not justified; just as the Flynn effect’s increase was caused by society training examinees in the tasks that the IQ tests measure, the reverse is true. When society does not emphasize the abilities IQ tests measure, IQ scores stabilize or even reverse. For example, in Norway, performance on an IQ test’s mathematics calculation subtest has decreased since schools started allowing students to use calculators in math classes. In another study in Kuwait, implementation of an Islamic education curriculum may have led to a decrease in IQs. This shows that no one is getting stupider in these countries; rather, what people are being taught and what the tests measure is less aligned than in the past.
While the Flynn effect is fascinating (as shown by the hundreds of studies on the topic), it is not as profound in its implications as James Flynn believed in the 1980s. People are not massively smarter than their grandparents, but they do have a different mix of cognitive strengths and weaknesses. This has implications for the education system and research, but the Flynn effect does not invalidate IQ tests at all.
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AuthorDr. Russell T. WarneChief Scientist
