A longitudinal study captures data over a period of time (days, week, months, or years) to understand the long-term effects of changes in products, processes, or environment.
Many usability methods like usability testing focus on initial use (learnability). Longitudinal studies focus on long-term effectiveness and satisfaction. A longitudinal study involves the repeated observations or examination of a group of users over time, at regular intervals, with respect to one or more study variables. Longitudinal studies are mainly done in order to follow changes in perception, behaviors, attitudes, and motivation of use. Such studies may be conducted over the duration of anywhere from a few days to several decades. Longitudinal studies can employ a range of methods including diaries, participant observation, critical incident reports, data logging, and repeated interviews.