If you missed Family Day last Monday, you may have missed an important opportunity to prevent your kids from smoking, drinking and using drugs.

Local governments and a national public-service ad campaign headlined by Jamie Lee Curtis and Barbara Bush told parents to eat dinner with their children on Sept. 26, based on a study that showed frequent family dining reduced the risk of substance abuse in kids by 50%.

"There is no more important thing a parent can do" to reduce the risk of their children using drugs, said Joseph A. Califano, Jr., chairman and president of Columbia University's National Center on Addiction and Substance Abuse, or CASA, the group behind the study. The report's claim was repeated in local media reports in Arizona, Florida and Indiana, among other places.

But before the government takes its war on drugs to the family kitchen, a closer look at the study is warranted. The study, based on a phone survey of 1,000 kids between 12 and 17 years old, and 829 parents, didn't show that family dinners cause a reduction in substance abuse. Instead, it found that teenagers who dined frequently with parents scored 50% lower on a substance-abuse risk assessment than did teenagers who didn't. That alone doesn't prove anything, and other factors could explain that correlation. What's more, the study found that other behavior actually had a greater influence on a teen's decision to use drugs, though those findings didn't fit as easily into a TV commercial.

Finally, the claim that frequent dinners reduce risk by 50% doesn't account for age -- a key failing. You might be unsurprised to learn that 17-year-olds are more likely to use drugs than 12-year-olds. Older teens are also the ones most likely to eat dinner away from their families.