Strengths and Limitations
This study has several strengths. Use of the app for randomization ensured that the researchers and participants had neither foreknowledge of treatment allocation nor the risk of identification during the intervention. Baseline demographic and smoking-related characteristics were well balanced between groups. The rigorous measurements of abstinence with biochemical verification suggested by the Russell Standard were applied in this study. Participants who declined to be involved in subsequent data collection were counted as smokers; therefore, the outcome findings in this study reflected somewhat conservative estimates. The transparency and clear framework of the intervention may allow future researchers to take advantage of our experiences.The study also has limitations. First, although efforts were made to ensure that both researchers and participants remained blinded to the randomization, a risk of breaking the blinding was present. For example, if a participant reported a problem with his or her program, the researchers needed to contact the information technology staff to investigate the problem, and they had the opportunity to identify the participant’s allocated group. Second, expired air carbon monoxide testing is the common method of detecting recent smoking and is recommended as a standard for the assessment of smoking cessation in trials. However, these biochemical tests are not perfect; expired air carbon monoxide can be detected only for approximately 24 hours after tobacco use. Bias can occur if a smoker stops smoking before providing a sample for testing, then resumes smoking after testing but reports that they have stopped smoking. Third, most of the participants were male and older than 18 years; therefore, caution should be used when generalizing our findings to the population level, as heterogeneity may exist. Fourth, although both groups had the same intervention period, the intervention group occasionally received 2 messages per day (vs 1 message per day in the control group) based on the framework of the intervention design. Therefore, the positive outcome of this study may be due to the different frequencies of contact. Fifth, there were only 6 female smokers in the cohort. Therefore, the study’s results might not be fully representative of female smokers.