Thread:Comments:Report finds teen substance abuse is top public health problem in US/correlation and causation

"CASA found that 90% of adults who have addictive disorders started using substances before the age of 18. In comparison, only 4% of Americans who abuse as adults started using these drugs when 21 or older."

This seems like a classic example of correlation &ne; causation (or at least not necessarily). The type of people who don't use drugs until 21, are also the type of people who have good self-control. If the addicts waited until 21, they might still have equally poor self-control, and still get addicted later in life.