South Korea had the highest average IQ worldwide, while the United States was below the global average, according to the International IQ Registry data.
South Korea ranked first with an average IQ of 107.54, up from the global average of 100. China and Iran were close behind, with 106.99 and 106.84, respectively.
The U.S. ranked 46th, with an average IQ of 98.99, just below the global average, behind countries like the United Kingdom, France, Spain, Italy, Germany and Canada.
The reliability of IQ tests has been debated. Cultural and socioeconomic backgrounds can affect the test's outcomes, as those designed in one cultural context may not translate effectively to others, psychologist Kathleen J. Ruby wrote for Medium in May.
Other factors, like test conditions and educational quality, can also affect the test results. Educational opportunity can enhance or impair IQ test performance, meaning that the test can reveal educational background as much as it shows cognitive capability.
However, despite these concerns, IQ tests have a "high proven degree of reliability and validity," according to the Brain Assessment Center.
"These studies are always difficult, divisive and contentious to interpret. It is difficult to factor out biases due to education and, more generally, to familiarity with the whole idea of tests," Professor John Hardy, the chair of Molecular Biology of Neurological Disease at the UCL Institute of Neurology, told Newsweek.
"This is not to say there are not differences, but I think the interpretations need to be taken with a pinch of salt."
The International IQ Registry explained that one reason some countries are below the global average is that China makes up around 18 percent of the world's population.
This means that China's high IQ sways the average slightly above what many other countries are calculated to have.
The countries with the lowest IQ included Angola, Congo, Gabon, and several other African nations. The International IQ Registry said this could be because Africa is the continent with the highest rate of infectious diseases, and those diseases "negatively affect cognitive development."
It also noted that countries with good dietary habits and lower levels of food poverty typically had higher average IQs.
The International IQ Registry conducted the same IQ tests in 2023 and found that 80 percent of the countries had similar IQ scores to those of the previous year, with a change of less than two points.
The countries with the largest changes included Honduras, Puerto Rico, Costa Rica, Qatar, Ireland, France, Israel and Canada, with a change of more than three points.
Israel's IQ changed the most, by over five points, meaning it went from ranking below the global average to above it at 102.18.
The data was collected through an IQ test based on Raven's Matrices technique, a non-verbal test used to measure general human intelligence and abstract reasoning.
Within the U.S., Massachusetts was found to have the highest average IQ out of all the states, with an average IQ of 104.3, six points above the national average.
As the state is well-known for its academic institutions like Massachusetts Institute of Technology and Harvard, it raises the question posed earlier: whether IQ tests also show a region's educational quality and opportunity.
The same can be said for the state at the bottom of the rankings, Mississippi, which had an average IQ of 94.2, as it ranks low on WalletHub's list of the nation's best school systems and is America's poorest state.
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