A longitudinal study is an observational research method in which data is gathered for the same subjects repeatedly over a period of time. Longitudinal research projects can extend over years or even decades.
In a longitudinal cohort study, the same individuals are observed over the study period. Cohort studies are common in medicine, psychology and sociology, where they allow researchers to study changes over time.
Here are some examples of longitudinal studies:
The Framingham Heart Study, which began in 1948 with 5,209 adult subjects from Framingham, Massachusetts, is the source of a great deal of current knowledge about heart disease. The study has yielded most of what is known about the effects of diet, exercise, and common medications such as aspirin on heart disease. The Framington Heart Study is now following the third generation of participants.
In 1971, the British Office of Population Censuses and Surveys began to follow a 1% sample of the British population. The study has correlated various outcomes, such as mortality and incidence of cancer, with variables such as employment status and housing.
The Terman Study of the Gifted, formerly known as the Genetic Studies of Genius, is the oldest and longest-running longitudinal study in the world. Lewis Terman began the study in 1921, at Stanford University, to observer the development and characteristics of gifted children over the lifespan. His initial purpose was to disprove the then-prevalent belief that gifted children were delicate physically and inclined to be socially inept. Terman's initial findings were that, other than intelligence and a tendency to be myopic, gifted children were not significantly different from their less-gifted peers.
The Canadian Longitudinal Study on Aging (CLSA) was designed to follow approximately 50,000 men and women between the ages of 45 and 85 for at least 20 years. CLSA researchers gather information on biological, medical, psychological, social, lifestyle and economic factors. The purpose is to gain knowledge about the effect of those factors, both separately and in combination, on the development of disease and disability as people age.