People who attended ninth grade in Finland with more than 1 peer who had been diagnosed with a mental disorder were 5% more likely to later receive a mental disorder diagnosis themselves compared with those with 1 or no classmates who’d been diagnosed, according to data from a population-based study involving more than 713 800 participants. The researchers enrolled participants when they were about 16 years old and followed them until they were either diagnosed with a mental health condition, left the country, or died.
