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Research Methods in the Social Sciences

Longitudinal Design*

Definition and Purpose

A longitudinal study follows the same sample over time and makes repeated observations. With longitudinal surveys, for example, the same group of people is interviewed at regular intervals, enabling researchers to track changes over time and to relate them to variables that might explain why the changes occur. Longitudinal research designs describe patterns of change and help establish the direction and magnitude of causal relationships. Measurements are taken on each variable over two or more distinct time periods. This allows the researcher to measure change in variables over time. It is a type of observational study and is sometimes referred to as a panel study.

What do these studies tell you?

  1. Longitudinal data allow the analysis of duration of a particular phenomenon.
  2. Enables survey researchers to get close to the kinds of causal explanations usually attainable only with experiments.
  3. The design permits the measurement of differences or change in a variable from one period to another [i.e., the description of patterns of change over time].
  4. Longitudinal studies facilitate the prediction of future outcomes based upon earlier factors.

What these studies don't tell you?

  1. The data collection method may change over time.
  2. Maintaining the integrity of the original sample can be difficult over an extended period of time.
  3. It can be difficult to show more than one variable at a time.
  4. This design often needs qualitative research to explain fluctuations in the data.
  5. A longitudinal research design assumes present trends will continue unchanged.
  6. It can take a long period of time to gather results.
  7. There is a need to have a large sample size and accurate sampling to reach representativness.


Sample Longitudinal Studies