Longitudinal studies characterise changes with respect to initial levels and rates of changes.
The future usefulness of longitudinal studies will depend increasingly on the preservation of biological specimens. The present overview focuses on the first two of these goals. Deeg distinguishes longitudinal studies from follow up studies that have two measurements. The present review includes some longitudinal studies that meet Deeg's definition as well as some follow up studies. Longitudinal Data and Detection of Disease and Functional Decline Pulmonary function and cardiac death .