Cohort Study: Definition & Examples

Instructor: Melanie Norwood

Melanie has taught several criminal justice courses, holds an MS in Sociology concentrating in Criminal Justice & is completing her Ph.D. in Criminology, Law & Justice.

In this lesson we will define what a cohort study is, what kinds of studies can be conducted using cohorts, why this method of social research is important, and a few challenges to conducting this kind of study.

What Is a Cohort Study?

Do you remember taking surveys about drug use in 8th grade and during high school? Those surveys were likely part of national studies that follow cohorts of youth, or youths in the same grades at the same time, to monitor nationwide drug use during adolescence.

A cohort study is a study that observes a group of individuals who meet a set of demographic, economic, educational or other criteria. These predetermined characteristics required of the subjects are known as selection criteria. Cohort studies are longitudinal, which means they monitor the effects of a treatment over time. By following a group of individuals who meet the selection criteria for a length of time, there's less need to collect participant background information throughout the study, because the scope of participant background was limited from the start.

Note that a cohort study differs from a cross-sectional study, which involves observing a population at one point in time. Cross-sectional studies provide a snapshot in time and are generally used to determine prevalence among a population.

Use of Cohort Studies in Criminology

Within the criminal justice field, cohort studies are used to examine the effectiveness and outcome of a diversion, intervention or treatment program. The long-term observation of subjects is particularly important here, as various factors that could affect the outcome of the program often come into play well after the program has completed. For instance, say that an ex-offender was laid off from his factory job and returned to a life of drug use, for which he was arrested and returned to prison. The fact that he was laid off and unable find equivalent work may be the reason that the offender returned to crime, rather than a failure on part of his treatment program. A cohort study would take these circumstances into account when evaluating the effectiveness of such programs.

Diversion programs within the criminal justice system, especially new programs, are particularly fond of cohort studies. That's due in part to the benefits that come to participants beyond the effects of the program: Criminal offenders may be allowed to avoid criminal charges by participating in a diversion program as part of a cohort study.

Examples of Cohort Studies

Cohort studies are used in a variety of fields, such as economics, ecology and business analytics. They're particularly popular in medicine, where cohort studies are used to examine the long-term effects of a specific treatment. In the realm of education, cohort studies have become very popular lately in the effort to determine the effectiveness of the new Common Core curriculum. However, for the purposes of this lesson, let's go over a couple of examples of the use of cohort studies within the criminal justice field:

Specialty courts, such as drug and prostitution courts, deal with offenders whose criminal records are comprised nearly exclusively of a specified type of crime, such as simple possession of drugs or solicitation of prostitution. These courts work with community programs to treat the offender and to help him or her avoid incarceration and criminal prosecution. In order to assess the effectiveness of these programs in preventing future crimes, a longitudinal cohort study is necessary to determine if these programs are meeting or falling short of their goals.

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