Which study has a cohort design?
A. Patients are randomly selected to use one of 2 drugs for arthritis symptoms and followed over time to assess treatment response
B. Patients who recovered from COVID-19 infection are matched and compared with patients who recovered from the seasonal flu for harmful lasting effects
C. A random sample of auto mechanics is tested for lead poisoning
The correct answer and explanation is:
Correct Answer: A. Patients are randomly selected to use one of 2 drugs for arthritis symptoms and followed over time to assess treatment response
A cohort study is a type of observational study in which a group of individuals sharing a common characteristic, known as a cohort, is followed over time to observe outcomes. The key feature of a cohort study is the temporal relationship between exposure and outcome, meaning that participants are observed after the exposure to see what outcomes develop.
Option A best fits the definition of a cohort study. In this example, patients are assigned to one of two arthritis drugs and are followed over time to monitor how their symptoms respond. The emphasis is on the forward-looking aspect of the study: participants are grouped based on the treatment (exposure), and researchers track them to see what outcomes occur. Although random assignment suggests an experimental design, if the study merely observes the outcomes without manipulating or controlling other variables beyond assigning treatments, it functions similarly to a cohort design. This design allows researchers to evaluate the causal relationship between drug use and symptom improvement.
Option B describes a retrospective case-control study. In this scenario, two groups are formed based on a known outcome—recovery from COVID-19 or the flu—and the researcher compares past exposures or effects. This is not a cohort design because it begins with the outcome rather than the exposure and looks backward in time.
Option C represents a cross-sectional study. It involves measuring exposure (lead levels) at a single point in time in a randomly selected group (auto mechanics). There is no follow-up period, and it does not assess changes over time, which eliminates it as a cohort design.
Therefore, Option A is the only choice that meets the criteria for a cohort study due to its prospective nature and observation of outcomes over time.