A “longitudinal study” involves observing the same group of individuals over an extended period of time. This allows researchers to look at changes that occur over time. The Twin Registry is an ideal setting for researchers to perform longitudinal studies, since most of our members continue to participate in Registry studies.
All members of the Twin Registry fill out the Enrollment Survey when they join the Registry. Many twins have also responded to the Health Survey and/or the Health and Wellbeing Survey. Some of our questions appear on more than one survey. In the longitudinal data analyses described below, researchers analyzed the responses of the same group of twins at two different points in time. By studying the same group at two time points, researchers can see how twins may change over time, and better understand what may cause those changes.