Machine learning prediction of blood alcohol content: A digital signature of behavior

Some people use digital devices to track their blood alcohol content (BAC). A BAC-tracking app that could anticipate when a person is likely to have a high BAC could offer coaching in a time of need. Kirstin Aschbacher shares a machine learning approach that predicts user BAC levels with good precision based on minimal information, thereby enabling targeted interventions.

Individuals can track their blood alcohol content (BAC) using commercially available devices, providing an opportunity for behavioral health interventions such as personalized messaging to target specific users at high-risk times or locations. To do so, a machine learning (ML) model would need to predict user BAC levels with high precision based on minimal information, such as timestamps, geolocation, and device/app engagement. Kirstin Aschbacher shares a machine learning approach to identify a digital signature of self-monitored BAC levels that predicts the times, locations, and circumstances under which a user is likely to exceed the legal BAC driving limit of 0.08%. Kristin and her teammates analyzed over 1 million data points from 33,452 distinct users of the BACtrack device (with established accuracy comparable to police-grade devices) collected between 2013 and 2017. Extensive feature generation was performed on BAC levels, app engagement, timestamps, and geolocation. They used census data to quantify zip codes by % rural/urban and integrated state-level motor vehicle death rates from the Center for Disease Control. Feature selection was performed using a gradient-boosted classification tree model (XGBoost; learning rate=0.1, max depth=5; boosting rounds=30). They optimized around precision specifically because commercial devices that employ ML-driven strategies to reach out to users should consider that recommendations made on the basis of low precision (predicting a user has a high BAC when they do not) could harm product trust or engagement. In a separate test set, they predicted whether BAC≥0.08% for a given user at a given time and location, with an average precision (positive predictive value) of 79%. The most predictive features in rough order of importance were users’ prior behavior (average BAC, subjective estimation of their BAC, tracking frequency, engagement quantity), temporal features (time of day/day of week), and geolocation (elevation, distances traveled between subsequent measurements, country, rural/urban percentage). Join in to learn how BAC levels exceeding the safe legal driving limit of 0.08% can be predicted with good precision using machine learning to quantify a digital phenotype. BAC prediction from minimal information establishes the foundation to conduct precision medicine behavioral interventions using a digital app and BAC tracking device. Kirstin wants to acknowledge and thank her UCSF coauthors on this work: R. Avram, G. Tison, K. Rutledge, M. Pletcher, J. Olgin, and G. Marcus.