A longitudinal study is a research design that involves repeated observations of the same variables (e.g., people) over extended periods of time. In these studies, researchers observe and collect data on a number of variables without trying to influence those variables.

Longitudinal studies are often used in social-personality and clinical psychology, to study rapid fluctuations in behaviors, thoughts, and emotions from moment to moment or day to day; in developmental psychology, to study developmental trends across the life span; and in sociology, to study life events throughout lifetimes or generations.

The duration of a longitudinal study can range from a few weeks to several decades, but they usually last at least a year.

There are several types of longitudinal studies, including:

• Panel Study: Involves sampling a cross-section of individuals at specific intervals for an extended period.
• Cohort Study: Samples a group of people with a common characteristic. Researchers observe a population based on the shared experience of a specific event, such as birth, geographic location, or historical experience.
• Retrospective Study: Uses already existing data, collected during previously conducted research with similar methodology and variables.

Longitudinal studies have several advantages:

• They allow researchers to follow their subjects in real time, providing insight into cause-and-effect relationships.
• They provide unique data and allow identifying trends.

However, they also have disadvantages:

• They are time-consuming and often more expensive than other types of studies