Longitudinal Research: Definition & Methods

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  • 0:00 Definition
  • 1:11 Methods
  • 2:43 Examples
  • 3:34 Advantages and Disadvantages
  • 4:15 Lesson Summary
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Lesson Transcript
Instructor: Peggy Olsen
Longitudinal research is used to study individuals at different stages in their lives. One group is studied over many years. Learn more about longitudinal research through examples and test your knowledge with quiz questions.


Have you ever wondered how developmental psychologists study changes over a lifespan? How do children's career aspirations develop over time? How does divorce affect children? How stable is personality? When do developmentally delayed children receiving special services catch up with their peers, if they do? What are the physical and mental health consequences of being in a war zone? Longitudinal research can answer those questions and more.


Psychologists try to provide answers to these questions using correlational research, which does not establish cause and effect, but only a relationship between two factors. A longitudinal study is correlational research which follows one group of individuals over a long period of time, perhaps decades. Researchers must evaluate the subjects at a minimum of two different time periods so they can be compared. Frequently, researchers meet with the subjects many times on a regular basis, for example every two months or every five years. The length of time is dependent on the topic of the research, the length of the study, and the age of the subjects.


How might a psychologist study the health effects of being in a war zone? After reviewing other research, psychologists would design a study, which requires making decisions about their methods.

  • Length of Study: Researchers must consider how long the subjects need to be evaluated in order to answer their research question and how often they will be evaluating the subjects. If interested in the initial effects, researchers might choose to study the group for one year after they return. If they are interested in long-term effects, they may choose to continue for 20 years.
  • Sample size: Researchers must decide who to research and how many subjects to include. The type of longitudinal study they choose will help them determine. If they choose one battalion of soldiers who served together in the war zone they would be doing a cohort study, a study that follows a group of people linked in some way.

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