Understanding Cohorts and How to Use them in Research

Get to Know this Common Research Tool

Smiling school children, members of the same age and educational cohort, pose in front of a world map.
Dave Nagel/Getty Images

What is a Cohort?

A cohort is a collection of people who share an experience or characteristic over time and is often applied as a method of defining a population for the purposes of research. Examples of cohorts commonly used in sociological research include birth cohort (a group of people born during the same period of time, like a generation) and educational cohort (a group of people who begin schooling or an educational program at the same time, like this year's freshman class of college students).

Cohorts can also be composed of people who shared the same experience, like being incarcerated over the same period of time, experiencing a natural or man-made disaster, or women who have terminated pregnancies during a particular time period.

The concept of a cohort is an important research tool in sociology. It is useful for studying social change over time, by comparing the attitudes, values, and practices on average of different birth cohorts, and it is valuable to those seeking to understand the long-term effects of shared experiences. Let's take a look at some examples of research questions that rely on cohorts to find answers.

Conducting Research With Cohorts

Did all people in the U.S. experience the Great Recession equally? Most of us know that the Great Recession that began in 2007 resulted in a loss of wealth for most people, but social scientists at Pew Research Center wanted to know if those experiences were generally equal, or if some had it worse than others.

To find this out, they examined how this massive cohort of people--all adults in the U.S.--might have had different experiences and outcomes based on membership in sub-cohorts within it. What they found is that seven years later, most white people had recovered most of the wealth they had lost, but Black and Latino households were harder hit than white ones, and instead of recovering, they continue to lose wealth.

Do women regret having abortions? It's a common argument against abortion that women will experience emotional harm from having the procedure in the form of prolonged regret and guilt. A team of social scientists at the University of California-San Francisco decided to test whether this assumption is true. To do this, the researchers relied on data collected through a phone survey between 2008 and 2010. Those surveyed had been recruited from health centers across the country, so, in this case, the cohort studied is women who terminated pregnancies between 2008 and 2010. The cohort was tracked over a period of three years, with interview conversations happening every six months. The researchers found that contrary to popular belief, the vast majority of women--99 percent--do not regret having an abortion. They consistently report, immediately after and as long as three years later, that terminating the pregnancy was the right choice.

In sum, cohorts can take a variety of forms, and serve as useful research tools for studying trends, social change, and impacts of certain experiences and events. As such, studies that employ cohorts are very useful for informing social policy.

Updated by Nicki Lisa Cole, Ph.D.