A causal discovery framework for digital phenotyping.

Digital phenotyping, the moment-by-moment quantification of human behavior using data from personal devices and sensors, has shown great promise in predicting mental health outcomes. However, the field is reaching a 'predictive plateau,' where models, while accurate, are often opaque black boxes that offer limited insight into underlying mechanisms of well-being. This paper proposes a fundamental paradigm shift from predictive classification to structural causal modeling. We introduce a two-stage computational framework that first learns unified daily behavioral embeddings from multimodal sensor data using a CNN-based encoder, and then applies neuro-symbolic causal discovery to infer interpretable directed graphs of behavioral-psychological dynamics. In our evaluation, we observed clear signs of this predictive plateau: even deep embedding models performed only slightly better than chance in stress prediction (best AUC = 0.532). By comparison, the causal approach identified candidate time-lagged associations; for example, lower levels of sleep activity ([Formula: see text]) and reduced mobility ([Formula: see text]) often appeared as preceding indicators of stress episodes. Dimensionality reduction via PCA retained five principal components explaining approximately 85% of the variance, enabling post-hoc interpretation of candidate behavioral components such as "Stationary Social Engagement." We define these components and their associated edge weights as candidate causal biomarkers: hypothesis-generating indicators of possible lagged behavior-stress relationships, rather than confirmed interventional causal effects.