According to a group of Norwegian researchers, spending more time at school may possibly increase ones intelligence. Through looking into the data of more than 107,223 students, researchers found that students' IQ were raised after the regional governments in Norway increased the schooling years of compulsory education. Between 1955 and 1972, the regional governments have increased compulsory schooling from seven to nine years, meaning that young adults left school at the age of 16 rather than 14. It is found that "An unusually large increase in both average education and average IQ is apparent at the same time as the reform was introduced." In addition, researcher said one additional year in school raised IQ by 3.7 points. Even though the link between a higher IQ and more education seems to be established, researchers say that its more difficult in determining whether spending more time in school actually improves IQ, because it is possible that children with a naturally higher IQ are those who choose to spend more time in the education system.