A longitudinal study is a research project that involves the observation of one or more sample groups over a long time, anywhere from a few months to 30 years or more. Such studies are invaluable to social science; they allow researchers to track changes and trends in individual behavior, societal development, relationships, and many other variables. A longitudinal study might be conducted by psychologists, sociologists, medical researchers, environmental scientists, anthropologists, or other experts who want to obtain reliable information about a population over time.
Longitudinal studies are especially important to research psychologists and sociologists who want to learn about correlations and trends in human behavior. A research psychology team might, for example, wish to find out if children of alcoholics are more likely than other children to develop behavioral problems and alcoholism later in life. The team would select a large population of very similar children, such as four-year-old males with alcoholic fathers in a given city. Researchers might interview the children, their parents, and their teachers annually over a period of 20 years, recording answers in the same manner each year. After the longitudinal study period, the researchers would organize data on each child and look for correlations in the results to determine if predictions can be made about other children of alcoholics.
Researchers have discovered many benefits of conducting longitudinal studies over laboratory experiments and short-term clinical trials. A longitudinal study allows scientists to observe changes in people as they live in the real world, interact with others, experience struggles, and enjoy successes. Using a longitudinal study research team can get a better idea of how a certain inherited disease, such as cystic fibrosis, affects people over the course of their lives. Longitudinal studies are also effective at tracking societal conditions, such as poverty rates, over several decades so that new public policies can be developed.
There are certain cases, however, when longitudinal studies are less accurate than direct, clinical experiments and trials. A pharmaceutical company that wants to test a new drug would likely conduct several clinical trials with many different sample groups instead of observing a single group of participants over time. The company would want to learn about immediate reactions and side effects during a controlled experiment to determine whether or not the drug is safe to market commercially. A longitudinal study simply introduces too many variables to pinpoint the effectiveness of a drug. Participants might not take the recommended doses, undergo positive or negative lifestyle changes, or report inaccurate information to researchers.