Middle and high school students who used electronic cigarettes were more likely to smoke real cigarettes and less likely to quit than students who did not use the devices, a new study has found. They were also more likely to smoke heavily. But experts are divided about what the findings mean.

The study’s lead author, Stanton Glantz, a professor of medicine at the University of California, San Francisco, who has been critical of the devices, said the results suggested that the use of e-cigarettes was leading to less quitting, not more.

“The use of e-cigarettes does not discourage, and may encourage, conventional cigarette use among U.S. adolescents,” the study concluded. It was published online in the journal JAMA Pediatrics on Thursday.

But other experts said the data did not support that interpretation. They said that just because e-cigarettes are being used by youths who smoke more and have a harder time quitting does not mean that the devices themselves are the cause of those problems. It is just as possible, they said, that young people who use the devices were heavier smokers to begin with, or would have become heavy smokers anyway.