Which study design assigns participants to two or more different treatment groups without randomization?

Which study design assigns participants to two or more different treatment groups without randomization?

• A. Randomized controlled trial
• B. Quasi-experimental
• C. Crossover
• D. Cohort

Answer: (B)

Nonrandom assignment of participants to multiple treatment groups is the hallmark of quasi-experimental designs. In these studies, researchers compare outcomes across different interventions but do not randomly assign who gets which treatment, so group differences can be influenced by selection bias. Quasi-experimental designs strive to draw causal inferences despite the lack of randomization by using methods to control for confounding, such as matching or statistical adjustments, or by analyzing changes over time. In contrast, a randomized controlled trial uses random assignment to create comparable groups, reducing bias; a crossover design has participants receive multiple treatments (often in a randomized order) and compare within the same individuals; and a cohort study observes outcomes in groups based on naturally occurring exposure without the investigator assigning treatments.

Nonrandom assignment of participants to multiple treatment groups is the hallmark of quasi-experimental designs. In these studies, researchers compare outcomes across different interventions but do not randomly assign who gets which treatment, so group differences can be influenced by selection bias. Quasi-experimental designs strive to draw causal inferences despite the lack of randomization by using methods to control for confounding, such as matching or statistical adjustments, or by analyzing changes over time.

In contrast, a randomized controlled trial uses random assignment to create comparable groups, reducing bias; a crossover design has participants receive multiple treatments (often in a randomized order) and compare within the same individuals; and a cohort study observes outcomes in groups based on naturally occurring exposure without the investigator assigning treatments.