prospective study

A longitudinal study is a correlational research study that involves repeated observations of the same items over long periods of time, often many decades. Longitudinal studies are often used in psychology to study developmental trends across the life span. The reason for this is that unlike cross-sectional studies, longitudinal studies track the same people, and therefore the differences observed in those people are less likely to be the result of cultural differences across generations. Longitudinal studies are also used in medicine to uncover predictors of certain diseases.
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A study in which persons are enlisted as subjects and are followed up periodically.

A study in which the study population is characterised at the start of the study and followed into the future. A population of people who do not (yet) have the disease under investigation is identified, and information is collected on the subjects' exposure to risk factors generally including nutritional factors. The frequency of the disease among subjects exposed to a particular risk factor during the follow up period is compared with the frequency among those who were not exposed.