longitudinal /lon′jəto̅o̅″dənəl/ [L, longitudo, length] , 1. pertaining to a measurement in the direction of the long axis of an object, body, or organ, such as the longitudinal arch of the foot. 2. pertaining to a scientific study (nonexperimental research design) that is conducted over a long period of time, such as the Framingham (Massachusetts) Heart Study of heart disease, with data collected from study participants at more than one point in time. Compare cross-sectional.
