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For nearly a century, human intelligence kept climbing. Each generation scored a little higher on standardized tests than the one before it, a trend so consistent that psychologists gave it a name. Then, sometime in the last twenty years, the climb stopped. In several countries, scores started sliding backward. Now a large-scale study of American adults has found the same pattern taking hold in the United States, and the researcher who ran the numbers didn’t believe her own results at first.
The ‘Flynn Effect’ Explains Why Your Grandparents Tested Lower Than You
The story starts with the Binet IQ test, developed in France and brought to the U.S. in the early 1900s, where it was given to schoolchildren, physicians, and immigrants arriving at Ellis Island. Starting in the 1930s, scores began creeping upward with each new generation. Educator James Flynn documented the pattern in 1984, and it became known as the Flynn Effect. Average scores rose by roughly three points per decade for most of the 20th century, regardless of which test was used.
Rising IQ Scores Were Linked to Longer Lives and Better Jobs
Researchers floated several explanations for the rise: improved nutrition, smaller families, earlier schooling, and more mentally demanding environments. Genetics was ruled out, since meaningful genetic shifts take far longer than a few generations. The trend mattered because higher IQ scores correlated with more education, stronger job prospects, and even longer, healthier lives. Scientists assumed the upward march would continue indefinitely, even if it eventually slowed. That assumption didn’t hold.
Europe Reported Falling Intelligence Scores First
Several European countries began reporting a reversal, with average test scores dropping instead of rising. The pattern raised an obvious question for researchers on the other side of the Atlantic: was the same thing happening in the United States? Northwestern University social scientist Elizabeth Dworak decided to find out, making it the subject of her graduate research. She and her colleagues set out to analyze cognitive test data collected from hundreds of thousands of American adults over more than a decade.
394,378 Americans’ Test Scores Went Under the Microscope
Dworak’s team pulled data from the Synthetic Aperture Personality Assessment (SAPA) Project, a free online personality survey that also scores users on cognitive ability. The analysis covered nearly 400,000 adults aged 18 to 90 who completed questions from the International Cognitive Ability Resource between 2006 and 2018. Rather than relying on one overall score, the researchers broke performance down into separate categories: matrix reasoning, letter and number series, verbal reasoning, and 3D spatial rotation.
Dworak Spent Weeks Checking Her Own Math
The results surprised even the lead researcher. “I spent weeks going back through all the code,” Dworak told New York magazine. “I thought I’d messed something up and would have to delay submitting. But then I showed my adviser, and he said, ‘Nope, your math is right.'” Composite scores declined across the 13-year period, and the drop showed up across every age group, education level, and gender. Adults aged 18 to 22 and those with less formal education saw the steepest declines.
Three of Four Cognitive Skills Declined, One Went Up
The breakdown revealed a more complicated picture than a simple across-the-board drop. Scores on matrix reasoning, letter and number series, and verbal reasoning all declined over the study period, pointing to weaker performance in abstract reasoning, logic, and vocabulary-based tasks. One category moved in the opposite direction: 3D rotation scores, which measure the ability to mentally manipulate objects in space, improved. Researchers floated a theory involving video games as a possible driver.
SAT and ACT Scores Have Also Been Sliding for Years
The pattern isn’t isolated to one study. Average scores on the ACT and SAT have both declined steadily over the past decade, a trend that predates generative AI tools and began before the pandemic, ruling out lockdowns or COVID-19 as the sole culprit. The timing lines up instead with the rise of smartphone use in the late 2000s. Times of London columnist James Marriott argues that the shift from print reading to scrolling has degraded how people process information.
Print ‘Privileges’ Logical Thinking, Columnist Argues
Marriott laid out his theory on a recent UnHerd podcast episode, arguing that books force readers to follow a logical case from start to finish in a way that short-form video doesn’t. He contrasted that with platforms like TikTok, where claims can be asserted without building an argument. Dworak’s study can’t confirm or rule out this theory. Because it relied on repeated snapshots of different people rather than tracking the same individuals over time, it can identify a trend but not pinpoint its cause.
A Mixed Verdict on America’s Changing Minds
The findings resist a tidy headline. Three cognitive domains slipped over 13 years while a fourth, spatial reasoning, climbed, suggesting the human mind isn’t simply getting weaker but adapting to a different set of daily demands. Dworak and her colleagues are now pursuing a follow-up study using four decades of data to dig deeper into what’s driving the shift. For now, the evidence points to a mind in transition, gaining in some areas while losing ground in others, not a straightforward decline.