Sadly, the answer is:

The methods of the study were as follows: "Individuals were recruited at e-cigarette retail locations in a large metropolitan city in the midwestern portion of the United States in July 2013. A total of 159 participants completed a brief 29-item self-report measure that assessed behaviors and perceptions of use."

The Rest of the Story

The study finds that e-cigarette use is associated with smoking status. In addition, e-cigarette use is associated with heavier smoking and with fewer periods of smoking abstinence.

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