eCigTracker™: assessing the validity of a smartphone app for estimating nicotine intake from electronic cigarettes.

BACKGROUND: Electronic Nicotine Delivery System (ENDS) use, particularly among young adults, is increasingly more popular than combustible cigarettes. Despite concerns over potential harm, standardized methods to assess ENDS device and liquid characteristics are lacking in behavioral surveillance and clinical studies. We adapted a dietary assessment method to develop the eCigTrackerTM app, which uses image-based tracking and app-based reminders (i.e. ecological momentary assessments) to prompt participants to capture device characteristics and estimate nicotine intake in real time. PURPOSE: This study reports on the development and validity testing of the eCigTrackerTM app. METHODS: ENDS users participated in two study phases: an in-lab phase and a 14-day in-field phase. For the in-lab phase, we estimated nicotine concentration and liquid volume consumed by comparing rater assessment vs. laboratory measurements. Image uploads and EMA were used to assess the feasibility of determining device use patterns and liquid consumption by device type during the in-field phase. T-tests and Cohen's d were used to evaluate rater vs. lab assessments, while ANOVA and Tukey HSD tested differences in ENDS liquid consumption by device type. RESULTS: Rater vs. lab assessments closely matched, with mean differences of -0.70 mL (t=-1.08, P=.28, -3.2% mean error) for liquid volume and 0.66 mg/mL (t = 0.50, P=.62, 3.0% mean error) for nicotine concentration. In-field assessments effectively captured device use patterns, showing significant differences in nicotine intake by device type (F(2,36)=18.71, P<.001). User satisfaction was high, with 82% reporting ease of use and 86% disagreeing the app complex. CONCLUSION: The eCigTracker™ app, developed primarily as a research tool to support real-time, image-based data collection in behavioral and epidemiological studies, is an accurate tool for measuring ENDS usage and estimating nicotine intake across diverse settings.