The PhasED Framework: A Measurement Theory-Based Approach to Algorithm Development and Evaluation

Wearable devices are essential to physical activity research, yet heterogeneous calibration protocols yield noncomparable estimates of key metrics (sedentary time, step counts, and moderate to vigorous physical activity). We introduce the PhasED (Phased Evaluation and Development for Wearable Algorithms) framework, an evolution of a prior phase-based framework, that embeds measurement theory principles to improve comparability and real-world performance of algorithms. PhasED integrates three elements: (a) establish acceptable reference measurements and procedures with the goal of real-world application for key behaviors; (b) harmonize development and calibration procedures to enhance comparability of algorithm output across devices and wear locations; and (c) conduct rigorous real-world testing according to Phase III of PhasED, which requires the use of established reference measures in independent study populations to quantify algorithm accuracy and precision. We propose the use of several reference measures by summarizing evidence for the accuracy and precision of acceptable reference measures for three core outcomes: sedentary time, moderate to vigorous physical activity, and step counts. ... mehrWe also identify key research gaps and priorities: consensus operational definitions, commutable calibration protocols, and open-source benchmarking data sets for evaluation that span diverse populations and devices. Broad adoption of PhasED can align algorithm development across research groups and devices, yielding estimates that are accurate, precise, and comparable across studies, thereby strengthening translation into guidelines and public health surveillance.