Norwegian IQ Study Finds Decline Since 1975, Not Attributed to Genes

A study of 730,000 Norwegian male conscripts born between 1962 and 1991 shows that average IQ scores, which had risen steadily throughout the 20th century, began to fall after 1975. The decline amounts to roughly seven points per generation. Researchers Bernt Bratsberg and Ole Rogeberg, working at the Centre Ragnar Frisch in Oslo, found that the drop occurs even among brothers, indicating that genetic factors are unlikely to explain the trend. They suggest environmental changes as the more plausible cause.

An American study cited by the authors reported a mixed pattern: verbal reasoning scores decreased while spatial abilities improved, highlighting that the phenomenon may vary across populations.