Longitudinal Study

Longitudinal studies follow the same subjects or a population over time. Because the same population is followed over time, changes collected from different observations can be attributed to individual changes rather than different samples of subjects.

Subjects in longitudinal studies are followed over various period of time, sometimes for decades. Such studies can relate incidence of cancer in a given population to certain population variables.

Groups of subjects are followed, one exposed to certain risk factors and the unexposed control. The groups are followed and the incidence rates are followed, thus attributing the disease to certain risk factors. Longitudinal research studies can evaluate biological and physiological processes associated with aging.

The problem with using longitudinal study design is that large numbers of patients must be followed for long periods of time to give statistically meaningful results. In addition, long-term commitment of funds and resources must maintain the study. This can be an issue if the disease, such as cancer, has a long induction period from exposure from the hazard to the symptomatic disease.

An advantage of the longitudinal method is that historical controls can be used in order to follow populations that have been exposed to a certain risk factor and to accumulate data through intensive documentation of growth and change on the same individuals.