RESUMO
BACKGROUND: Ecological momentary assessment (EMA) is a popular method for understanding population health in which participants report their experiences while in naturally occurring contexts in order to increase the reliability and ecological validity of the collected data (as compared to retrospective recall). EMA studies, however, have relied primarily on text-based questionnaires, effectively eliminating low-literacy populations from the samples. OBJECTIVE: To provide a case study of design of an EMA mobile app for a low-literacy population. In particular, we present the design process and final design of an EMA mobile app for low literate, Mexican American women to record unhealthy eating and weight control behaviors (UEWCBs). METHODS: An iterative, user-centered design process was employed to develop the mobile app. An existing EMA protocol to measure UEWCBs in college-enrolled Mexican American women was used as the starting point for the application. The app utilizes an icon interface, with optional audio prompts, that is culturally sensitive and usable by a low-literacy population. A total of 41 women participated over the course of 4 phases of the design process, which included 2 interview and task-based phases (n=8, n=11), focus groups (n=15), and a 5-day, in situ deployment (n=7). RESULTS: Participants' mental models of UEWCBs differed substantially from prevailing definitions found in the literature, prompting a major reorganization of the app interface. Differences in health literacy and numeracy were better identified with the Newest Vital Sign tool, as compared with the Short Assessment of Health Literacy tool. Participants had difficulty imagining scenarios in the interviews to practice recording a specific UEWCB; instead, usability was best tested in situ. Participants were able to use the EMA mobile app over the course of 5 days to record UEWCBs. CONCLUSIONS: Results suggest that the iterative, user-centered design process was essential for designing the app to be made usable by the target population. Simply taking the protocol designed for a higher-literacy population and replacing words with icons and/or audio would have been unsuccessful with this population.