“The very best way to help them quit is to offer them money,” Dr. Scott Halpern, associate professor at the University of Pennsylvania and lead author of the study told CBS News.

The study, published by The New England Journal of Medicine, looked at 6,006 smokers at 54 U.S. companies.

Of those, the researchers classified 1,191 as “willing to quit,” according to Reuters, then gave them different tools to help.

One group received literature about the benefits of quitting along with positive encouragement to quit smoking (less than 1% of those quit for six months). Another group was given free stop-smoking aids like gum, patches, and lozenges (2.9% of those quit). A third group received free e-cigarettes — electronic devices that vaporize nicotine — of the flavor of their choice (4.8% of those stopped smoking).

Two other groups received an added bonus: cash.

One group received both stop-smoking items and a cash reward: $100 after the first month, a $200 bonus at the three month mark, and $300 more at the six month mark. In the end 9.5% of them quit.

The other was given any stop-smoking product they wanted, and the threat that $600 in an account would be taken away if they smoked. A whopping 12.7% made it to the six month mark.

Half of those who reached the six month mark continued to abstain from smoking for a year.

“People are much more motivated to avoid losing $100 than they are to gain $100, even though, economically, they are flip sides of the same coin,” Halpern told Reuters.

The study comes at a time when the effectiveness of e-cigarettes in helping people quite smoking is being debated. While the Centers for Disease Control and Prevention say that e-cigarettes are less harmful than traditional cigarettes, it warns that there are still risks associated with them because they contain “cancer-causing agents.”

“E-cigarettes are not currently approved by the FDA as a quit smoking aid,” according to the CDC. “The U.S. Preventive Services Task Force, a group of health experts that makes recommendations about preventive health care, has concluded that evidence is insufficient to recommend e-cigarettes for smoking cessation in adults, including pregnant women.”

In Halpern’s view, the results of the study show that “we cannot detect any evidence that [e-cigarettes] are better than offering free conventional smoking cessation aids or just providing information.”

Critics of the study told CBS News that the study didn’t actually show that e-cigarettes weren’t useful, but just compared it to other methods.

The results also gives employees a better sense of how much it would cost to get employees to stop smoking.

“The best estimates are, it costs $3,000 to $6,000 more per year to employ a smoker rather than a non-smoker,” Halpern told Reuters. “So even if these programs cost $800 to $1000, they would be highly cost-saving from the standpoint of the employer and the insurer.”

The study was sponsored by employee wellness company Vitality Group.