BACKGROUND Transition-aged youth (TAY) who experience homelessness are exposed to environments that contribute to risk behavior. However, few studies have examined how access to housing may affect the health risk behaviors of transition-aged youth (TAY) experiencing homelessness. OBJECTIVE This paper describes the Log My Life (LML) study that uses an innovative, mixed-methods approach based on geographically explicit ecological momentary assessment (EMA) through cell phone technology to

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... nd the risk environment of TAY who have either enrolled in housing programs or are currently homeless. METHODS For the quantitative arm, TAY respond to momentary surveys via a smartphone application that collects geospatial information repeatedly during a 1-week period. Both EMAs and daily diaries are prompted to explore within-day and daily variations in emotional affect, context, and health risk behavior, while also capturing infrequent risk behaviors such as sex in exchange for goods or services. For the qualitative arm, a purposive subsample of participants who indicated engaging in risky behaviors are asked to complete an in-depth qualitative interview using an interactive, personalized geospatial map rendering of EMA responses. RESULTS To date, 160 participants completed the full seven days of the study protocol. Compliance with EMA and daily diary surveys was generally high (between 76.6% and 87.2%). CONCLUSIONS Mixing the quantitative and qualitative arms in this study will provide a more complete understanding of differences in risk environments between homeless and housed TAY. Furthermore, this approach can improve recall bias and enhance ecological validity.