Implementation of Self-Initiated Event-Contingent Ecological Momentary Assessment for Environmental Exposures: Prospective Observational Study.

Background: Retrospective questionnaires are commonly used to assess exposure to unpleasant environmental stimuli, such as sounds and odors, but they are vulnerable to recall and salience biases. Ecological momentary assessment (EMA) is often proposed as a superior alternative because it captures experiences close in time to their occurrence. However, self-initiated, event-contingent EMA protocols require sustained participant engagement, and little is known about their feasibility, reporting completeness, and implementation challenges under naturalistic conditions. Objective: This study aims to evaluate a self-initiated smartphone-based EMA protocol for documenting unpleasant sound and odor exposures and to examine the implications of observed EMA use, the time between the first and last report, and reporting completeness for interpreting data obtained using the self-initiated EMA. Methods: Participants completed a 3-month study using a self-initiated, event-contingent smartphone-based EMA protocol alongside baseline and follow-up retrospective questionnaires. Individuals with and without self-reported environmental sensitivity to sounds or odors were offered access to a web-based EMA app for self-initiated reporting of exposure events. Reporting behavior measures included observed EMA use, the number of submitted reports, the time between the first and last submitted reports, reporting completeness (self-reported missed events), and barriers to app use. Analyses were primarily descriptive. Results: Of 104 participants (environmentally sensitive [ES], n=42; nonenvironmentally sensitive [NES], n=62), EMA reporting was limited, with 15 (36%) ES participants and 22 (35%) NES participants submitting at least one report ( Conclusions: Under naturalistic conditions, this 3-month self-initiated, event-contingent EMA protocol demonstrated limited observed use, declining report submissions over time, and substantial self-reported incompleteness. These findings arise from 1 specific implementation and should not be generalized to self-initiated EMA protocols using different sampling procedures, onboarding, participant support, reminders, incentives, or technologies. Nevertheless, they highlight the importance of reporting implementation characteristics when interpreting data from self-initiated, event-contingent EMA studies.