longitudinal research design

A basic type of research method in which subjects are tested one or more times after initial testing. Typically, subjects are assigned randomly to an experimental group (e.g. a group that performs a specific type of training) and a control group after the initial testing. Both the experimental and the control groups are tested again simultaneously one or more times during the period of the study. In this way, the effects of an experimental procedure can be measured over a period of time.