CLAYTON, Mo. (AP) _ About half of Missouri's youth have placed a bet by age 20, according to a new survey by a Washington University professor.

The survey of about 350 people age 14 to 25 from Missouri households found nearly 40 percent in that age span had already gambled for money or something of personal value. The survey defined gambling as taking part in at least one type of gambling activity more than five times.

Youth gambled a variety of ways, but those surveyed said the lottery, card games and betting on sports were the most common.

The survey was done by Renee Cunningham-Williams, an associate professor at the George Warren Brown School of Social Work at Washington University.

The average age for gambling on casino-type games was 19 to 20, she said. And by age 20, she estimated 50 percent of Missouri youth would have placed a bet or gambled based on the survey findings.

Cunningham-Williams presented her research Friday at the Midwest Conference on Problem Gambling and Substance Abuse, which brought together about 200 participants to talk about addiction, treatment and related research in the St. Louis suburb of Clayton.

It wasn't clear precisely how much illegal gambling the youths engaged in, since the survey involved both children too young to legally gamble and young adults old enough to legally make wagers. In Missouri, people must be 18 to play the lottery and 21 to get onto the gaming floor in a casino.

Cunningham-Williams found 11 percent of those surveyed could be considered at-risk gamblers, 2.5 percent could be considered problem gamblers and 0.1 percent could be deemed compulsive gamblers.

Because she had not surveyed the same youths over time, Cunningham-Williams said, it's not yet clear if the youth engaging in risk-taking behavior might pass out of it as they grow older. They may develop a better understanding of the consequences, she said.

Cunningham-Williams said early intervention could be helpful in reducing risk-taking gambling behaviors. "If we intervene now, we may prevent problems down the road," she said.

The conference was partially funded by the Substance Abuse and Mental Health Services Administration and involved agencies in Iowa, Missouri, Kansas, Nebraska and Oklahoma, event organizers said.

Cunningham-Williams' research was supported by the Greater Kansas City Community Foundation, with funds provided by the Port Authority of Kansas City.

Phone calls to seek outside comment on the research were not immediately returned.