After having risen steadily since Wold War Two, generations born since 1975 have seen their scores drop, signalling the end of a trend – known as the Flynn effect.
The Flynn effect describes the rise in average IQs over the past 60 to 70 years by roughly three points a decade.
Scientists have described the results as “pretty worrying”, according to The Times of London.
The decline is attributed to how languages and maths are taught in schools, scientists have suggested, but it may also be due to increased immigration.
A psychologist at the University of Edinburgh, Stuart Ritchie, told the newspaper: “This is the most convincing evidence yet of a reversal of the Flynn Effect.”
IQ scores have fallen since the turn of the millennium, according to two previous British studies suggesting a drop of between 2.5 and 4.3 points every ten years. Their results were however dismissed as inconclusive.
Ole Rogeburg and Bernt Bratsberg, of the Ragnar Frisch Centre for Economic Research in Oslo, found that Norwegian men’s IQs were lower than the scores of their fathers when they were the same age.
They analysed the score results of a standard IQ test from a huge sample of over 730000 men – those who had reported for national service between 1970 and 2009. Their findings were published in the Proceedings of the National Academy of Sciences of the United States of America Journal (PNAS).
In December 2017, scientists revealed in a seperate study that fish regularly included in a diet, improves children’s intelligence as well as helping them to sleep better. Nine to 11-year-olds who eat fish at least once a week scored almost 5 points higher in IQ tests to those who do not.
Done by US researchers, more than 500 children took an IQ test which also considered verbal and written communication skills. “After taking into consideration factors such as their parental education, occupation and marital status, it found children who eat fish least once a week score 4.8 points higher than those who never do,” the Daily Mail reported.
Even those whose meals sometimes include fish scored 3.3 points higher.