IQ Score Trends Over Time — The Flynn Effect & Beyond

What Is the Flynn Effect?

The Flynn Effect refers to the well-documented observation that IQ test scores have been rising in virtually every country where data has been collected, at an average rate of roughly 3 points per decade. The phenomenon is named after New Zealand political scientist James R. Flynn, who first brought it to widespread academic attention in the 1980s.

Flynn analyzed military conscription records and standardized test data from over a dozen countries, including the United States, the Netherlands, Belgium, France, and Japan. In every case, he found that people who took the same IQ test in a later decade scored higher than those who took it in an earlier decade. The gains were not small: over the course of the 20th century, average IQ scores in many countries rose by 15 to 20 points, which is equivalent to one full standard deviation.

This means that someone who scored 100 (average) in 1950 might score only around 80 to 85 on the norms of a test standardized in 2020. The reverse is also true: a person scoring 100 today would likely have scored 115 or higher on 1950 norms. This has profound implications for how we interpret historical IQ data.

James Flynn's Research and Key Findings

James Flynn (1934–2020) was a professor at the University of Otago in New Zealand. Although he was a political scientist by training, his meticulous analysis of intelligence test data made him one of the most influential figures in IQ research. His key findings include:

• Universal gains: IQ score increases were found in every country with available data, not just wealthy Western nations.
• Largest gains on abstract reasoning: The biggest score increases occurred on tests of fluid intelligence—abstract reasoning and pattern recognition—rather than on tests of vocabulary or general knowledge (crystallized intelligence). Raven's Progressive Matrices, a nonverbal pattern-matching test, showed some of the most dramatic gains.
• Gains were not due to genetics: The changes happened far too quickly (within a single generation) to be explained by genetic evolution. Flynn argued that environmental factors must be responsible.
• Real cognitive improvement, not just test sophistication: While some critics suggested people simply became better at taking tests, Flynn presented evidence that the gains reflected genuine improvements in certain types of abstract thinking.

Flynn's work fundamentally changed how psychologists think about IQ. Before his research, many assumed intelligence was largely fixed and stable across generations. His findings showed that the environment plays a far larger role than previously thought. You can read more about the interplay between genetics and environment in our guide on IQ: genetics vs. environment.

Possible Causes of Rising IQ Scores

Researchers have proposed several explanations for the Flynn Effect, and the reality is likely a combination of multiple factors:

• Better nutrition: Improved diets, particularly in early childhood, have been linked to brain development. The near-elimination of severe malnutrition and iodine deficiency in developed countries correlates with IQ gains.
• More and better education: Over the 20th century, average years of schooling increased dramatically worldwide. Schools increasingly emphasize abstract and analytical thinking, which is precisely what IQ tests measure.
• Smaller families: With fewer children per household, parents can devote more time and resources to each child's intellectual development.
• More cognitively stimulating environments: Modern life exposes people to far more complex visual information, technology, and abstract problem-solving than previous generations faced. Video games, computers, and even television require more cognitive processing than many activities of the past.
• Reduced exposure to toxins: The removal of lead from paint and gasoline, better prenatal care, and reduced childhood illnesses have all contributed to healthier brain development.
• Improved healthcare: Better medical care, vaccinations, and lower infant mortality rates mean more children reach their full cognitive potential.

The Reverse Flynn Effect: Are Scores Now Declining?

Starting in the 1990s, researchers began noticing something unexpected: in several highly developed countries, IQ score gains were slowing down, stalling, or even reversing. This phenomenon has been called the reverse Flynn Effect or negative Flynn Effect.

Studies from Norway, Denmark, Finland, France, and the United Kingdom have reported declining average IQ scores among cohorts born after roughly 1975. A notable 2018 study by Bratsberg and Rogeberg, using Norwegian military conscription data, found a decline of about 0.2 IQ points per year among those born after 1975, reversing the gains seen in earlier decades.

Proposed explanations for the reversal include:

• Diminishing returns of environmental improvements: Once a society has largely eliminated malnutrition and provides universal education, the gains from further improvements may plateau.
• Changes in education: Some researchers argue that shifts in teaching methods, reduced emphasis on certain types of analytical thinking, or increased screen time may play a role.
• Environmental factors: New environmental exposures, such as microplastics or endocrine disruptors, have been speculatively linked to cognitive changes, though evidence is still limited.
• Immigration and demographic shifts: Some analyses have found that the decline is present even within families (comparing siblings), suggesting it is not simply a compositional effect.

It is important to note that the reverse Flynn Effect has not been found everywhere. In many developing countries, IQ scores continue to rise as nutrition, healthcare, and education improve.

What This Means for Comparing Scores Across Eras

The Flynn Effect has several practical implications for anyone interpreting IQ scores:

• Old test norms produce inflated scores: If you take an IQ test that was normed 20 years ago, your score may be artificially high because the comparison group's average was lower. This is why test publishers periodically re-standardize their instruments.
• Historical comparisons are misleading: Claims that a historical figure "had an IQ of 160" are speculative. The testing standards, reference populations, and even the definition of intelligence have changed over time.
• Legal and clinical implications: In the United States, the Flynn Effect has been cited in legal cases involving intellectual disability determinations, particularly in capital punishment cases. A score of 71 on an outdated test might actually be equivalent to a score below 70 on current norms, which has significant legal consequences. Learn more about what a 70 IQ score means clinically.
• Your score reflects your generation: An IQ of 100 today represents a different level of cognitive performance than an IQ of 100 did in 1960. You can only meaningfully compare your score to people tested with the same version of the same test, normed in the same era.

For a deeper understanding of how IQ scores are calculated and normed, see our guide on how IQ is calculated. If you are curious about where your own score falls today, you can take our free IQ test to get a current estimate.