Abstract
Ambulatory assessment is a class of methods that use mobile technology to understand people's biopsychosocial processes in natural settings, in real time, and on repeated occasions. In this essay, we discuss the rationale for ambulatory assessment including the benefits of measuring people in the real world (greater ecological validity, better understanding of people in contexts), in real time (avoidance of memory bias, greater sensitivity for capturing change), and over time (capturing within-person patterns and temporal trends). Then, we review the latest ambulatory assessment techniques for measuring experiences, behaviors, and physiology in daily life. Experiences such as emotions, physical pain, and daily stressors can be tracked using daily diaries and smartphone-based experience sampling. Behaviors such as activity, movement, location, and natural language use can be tracked using accelerometers, portable actigraphs, global positioning system (GPS) coordinates, and the electronically activated recorder (EAR). Physiological processes such as heart rate, blood pressure, and electrodermal activity can be measured using an array of ambulatory biosensors. Ambulatory assessment will continue to be revolutionized by smartphones, which are becoming integrated seamlessly into people's lives. Emerging trends include social sensing applications that make inferences about users' psychological processes based on multi-channel information collected from smartphones, emergence of “big data collection” whereby ambulatory assessment data is gathered en masse from large populations, and the growing field of mobile health. These trends raise questions around the protection of participants' privacy and the synthesis of immense amounts of digital data. Ultimately, these developments will narrow the separation between science and everyday life as ambulatory assessment becomes an integrated part of people's mobile lives.