New York, Dec 18 (IANS): Researchers have now claimed that kids who use e-cigarettes are more likely to take up smoking or smokeless tobacco.

The study, published in the journal Addictive Behaviors, says teenage boys who vaped were almost three times as likely to start smoking as other teen boys with similar risk profiles and more than two times as likely to try smokeless tobacco.

"For an ideal study, from a purely scientific perspective, we'd give everybody an e-cigarette, follow them for a few years and see if they start smoking, then rewind the clock and don't give them an e-cigarette," said study author Brittney Keller-Hamilton from Ohio State University in the US.

"Or we'd randomly assign kids to vape or not to vape. We can't do either of those things, obviously," Keller-Hamilton added.

So they looked to an advanced statistical approach -- "causal inference" -- in which they compared users and non-users of e-cigarettes who started the study with similar known risk factors for vaping based on a variety of factors, including alcohol use, marijuana use, impulsivity and their parents' education levels and tobacco history.

The research team identified two groups of young people who were equally likely to start vaping based on a number of factors, and then compared the outcomes over the course of the study.

They found that e-cigarette users were 2.7 times as likely to try smoking.

This research followed more than 1,200 boys from urban Franklin County and nine rural Appalachian counties in Ohio for two years. They were 11 to 16 years old when they entered the study.

The new findings support continued efforts to restrict access to tobacco products to those 21 and older and actions to discourage vaping among kids, including measures that make e-cigarettes harder to obtain and less appealing.

"I hope that our findings provide policymakers and others stronger evidence of the connection between e-cigarette use and tobacco use," the study authors wrote.