Okay, parents, here's some ammunition to use when your 14-year-old daughter falls for the 16-year-old player who just moved into the neighborhood. A national survey of 1,000 teens, released yesterday by Columbia University, confirms what you already suspect: It's dangerous for teenage girls to date older boys, particularly boys two or more years older.
It's also dangerous for girls or guys to spend a lot of time with a boyfriend or girlfriend, and to hang out with a group of sexually active friends.

The relationships teens keep are associated with risky behavior -- including smoking and illegal drug use -- according to a survey by Columbia University.
(Thad Allender -- Lawrence Journal-world Via AP)
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Why?
Because these pastimes are tightly connected to a slew of risks -- not only early sexual intercourse, but also drinking, smoking and illegal drug use, according to Columbia's National Center on Addiction and Substance Abuse.
The center is careful to say that risky dating patterns do not necessarily cause other negative behaviors. They simply signal that those other behaviors may be present -- if not always visible.
It's what scientists call the cluster effect, or what Mom and Dad mean when they look over the new friend and say, "He [or she] is bad news."
"There is a clear message for parents of 12- to 17-year-olds," says Joseph A. Califano Jr., the center president. "Make sure you are aware of the dating practices of your child and get to know your child's friends."
A striking number of the teens surveyed -- 45 percent -- said they knew friends who regularly use the Internet to view or download pornography. "I haven't seen that before. That's substantial and worth exploring," said Brett Brown, a sociologist and director of Child Trends, a research organization.
If their friends watched a lot of porn, the teens were more than three times as likely to smoke, drink and use illegal drugs than teens who had no such friends.
Other findings included:
Older boyfriends were common. Among 12-year-old girls who said they had a boyfriend, more than half said their boyfriends were older; among 17-year-old girls, three-fourths said the same thing. (One-third of all the teens polled said they had a boyfriend or girlfriend.)
Girls whose boyfriends were two or more years older were six times as likely to get drunk as girls who dated boys closer to their age. They were also six times as likely to have tried marijuana and more than four times as likely to smoke cigarettes. This finding, like the others, was controlled for age.
Fifty-six percent of those surveyed said they knew kids in their "close circle of friends" who were sexually active. More than a quarter of 12-year-olds said so; more than three-quarters of the 17-year-olds did.
Other organizations, notably the National Campaign to Prevent Teen Pregnancy, have reported that teens are more likely to have sex if they believe their peers are having sex. The Columbia report goes beyond that to say that teens who believed half or more of their friends were sexually active were more than six times as likely to drink; 31 times as likely to get drunk; 22 times as likely to have tried marijuana; and more than five times as likely to smoke.