Observing how something changes over time: longitudinal studies

Longitudinal studies, like their name, are long.

Often in research, scientists are curious about how time will affect a particular aspect of life. In order to study this relationship, they might create a longitudinal study.

A longitudinal study is the study of the same group of adult or child participants over a period of time. This time period could be anywhere from a couple of weeks to many years.

There are three major types of longitudinal studies.

• A panel study involves collecting information from the same participants at different points in time. For example, researchers might follow people of different ages learning a second language.
• A cohort study observes a sample group based on a specific event. For example, scientists may follow a class of Deaf students as they go from preschool to college.
• A retrospective study is a study that looks at a historical information and then selects a sample group. It’s similar to a panel study or a cohort study, but the events conclude before the study begins.

Longitudinal studies are beneficial because scientists are given the opportunity to study the development of both an individual and the target population as a whole. These studies provide researchers with a better sense of how their target population changes over time.

One disadvantage, however, is that longitudinal studies can take a long while to complete, which is not feasible for some research projects. Additionally, it can be difficult to complete the study because participants could potentially drop out of the study due to various reasons. These reasons may include participants moving away, changing schedules, or other circumstances. Often, even if a participant ends the study before its conclusion, the data they contributed is still helpful.

Longitudinal studies like this one have been useful in observing the differences in language development between children with autism, children with Down syndrome, and typically developing children. Our work at the Bergelson Lab involves a longitudinal study to observe how typically developing children learn and understand English.

What other questions about language acquisition could longitudinal studies answer?