Longitudinal studies follow the same group of people over a very long time. By doing this researchers can see which factors earlier in life are linked to problems later. Danish researchers managed to track 110 people from birth to the age of 40 and looked into the links between attention-deficit hyperactivity disorder (ADHD) and conduct disorder in childhood, and the later development of drink problems. They found that people who scored above average for both ADHD and conduct disorder were six times more likely to develop alcohol dependence by the age of 40. Both ADHD and conduct disorder independently increased the risk of developing a drink problem even if children only scored highly for one of these factors.
Knop, Joachim ... [et al] - Childhood ADHD and conduct disorder as independent predictors of male alcohol dependence at age 40 Journal of studies on alcohol and drugs March 2009, 70(2), 169-177