research designs in which the same group of individuals is observed repeatedly over an extended period. Data are collected at multiple time points without intervening or altering participants’ experiences. This approach allows researchers to track changes in health status, behaviors, or other variables over time and to identify factors that may be associated with those changes.
Abbreviation: LOS
Example
A research team enrolls 5,000 adults aged 30–50 and collects health data every two years for 15 years. They track diet, physical activity, and cardiovascular health measures without assigning any treatments. This longitudinal observational study allows the team to examine how lifestyle factors over time are linked to the development of heart disease.