longitudinal

In the new study, researchers analyzed data from the Avon Longitudinal Study of Parents and Children, a long-running study in the U.K. that has followed women and their children. The study began when the women were first pregnant, all in 1991 or 1992.
For the new report, the researchers looked at questionnaires that more than 5,300 of the children completed. The kids were surveyed at least three times between ages 13 and 18, and asked about the frequency of their use of drugs, alcohol and tobacco in the previous three months. They were also sent a follow-up survey by mail to measure these behaviors at age 21.
Researchers found that teenagers in the study who regularly used marijuana were 26 times more likely to have used other illegal drugs, such as cocaine, amphetamines or hallucinogens, by the time they reached early adulthood, compared with teens who hadn't smoked pot, according to the findings published online today (June 7) in the Journal of Epidemiology and Community Health.