How do we determine the impact of e-cigarettes on cigarette smoking cessation or reduction? Review and recommendations for answering the research question with scientific rigor

Abstract

Aims:

To propose a hierarchy of methodological criteria to consider when determining whether a study provides sufficient information to answer the question of whether e-cigarettes can facilitate cigarette smoking cessation or reduction.

Design:

A PubMed search through February 1, 2017 was conducted of all studies related to e-cigarettes and smoking cessation or reduction.

Settings:

Australia, Europe, Iran, Korea, New Zealand, United States.

Participants/Studies:

91 articles.

Measurements:

Coders organized studies according to six proposed methodological criteria: 1) examines outcome of interest (cigarette abstinence or reduction), 2) assesses e-cigarette use for cessation as exposure of interest, 3) employs appropriate control/comparison groups, 4) ensures that measurement of exposure precedes the outcome, 5) evaluates dose and duration of the exposure, and 6) evaluates the type and quality of the e-cigarette used.

Findings:

Twenty-four articles did not examine the outcomes of interest. Forty did not assess the specific reason for e-cigarette use as an exposure of interest. Twenty articles did not employ prospective study designs with appropriate comparison groups. The few observational studies meeting some of the criteria (duration, type, use for cessation) triangulated with findings from three randomized trials to suggest that e-cigarettes can help adult smokers quit or reduce cigarette smoking.

Conclusions:

Based on the proposed criteria, few studies claiming to address the effect of e-cigarettes on smoking cessation or reduction are of sufficient quality to inform the scientific question of interest. Studies with stronger measures and methods are needed to better inform the question of e-cigarette use for smoking cessation or reduction.