What is a cohort study?

A cohort study is a type of research study in which a group of people who share a common characteristic are followed over a period of time with evaluation at numerous times to examine differences in health outcomes and causal risk factors. 

What is a prospective vs. retrospective cohort study?

A prospective cohort study follows a group of people over a period of time and is future-oriented. The individuals have many similar characteristics, but differ by one variable (example: smoker vs. non-smoker). They are then followed to determine the incidence of the development of a certain condition or disease over a period of time. 

A retrospective cohort study uses pre-existing data to look backward at potential exposures and risks that may have led to an outcome. 

What are the benefits of a cohort study?

One of the major benefits of a cohort study is the ability to study various exposures, the combined effect of exposures, and multiple outcomes within the one selected cohort. Cohort studies are also typically easier to conduct and more affordable than randomized controlled trials. Another benefit of cohort studies is that the inclusion and exclusion criteria are typically less strict compared with experimental studies, therefore the results can be more easily generalized.

How is a cohort study conducted?

The first step in a cohort study is identifying the population. Once the population is selected, baseline data will need to be collected. Baseline data should help identify the “exposed” vs. the “non-exposed” for comparison. Follow-up data will be collected at specific periods of time. Once all data is collected, it will be analyzed to determine outcomes. 

What are the restrictions to a cohort study? 

Cohort studies have certain limitations and restrictions, including lack of randomization in the study population, inability to determine causation, having to follow the cohort for a very long period of time, and possible poor follow-up from participants.