What is the term for a research design that involves a comparison like an experiment but without random assignment of participants to groups?

What is the term for a research design that involves a comparison like an experiment but without random assignment of participants to groups?

• A. Quasi-experiment
• B. Randomized controlled trial
• C. Longitudinal study
• D. Cross-sectional study

Answer: (A)

When a study compares outcomes after an intervention but does not randomize participants into treatment and control groups, that design is a quasi-experimental design. The strength is that it still borrows a causal question and includes a comparison, but the lack of random assignment means groups can differ in ways other than the intervention. Those preexisting differences can influence outcomes, so causal conclusions are weaker than in a true randomized controlled trial. Researchers often try to compensate with pretests, matching, or statistical controls to reduce bias, but the potential for selection differences remains. This differs from a randomized controlled trial, which uses random assignment to create equivalent groups and bolster causal claims. It also differs from a longitudinal study, which follows the same individuals over time to observe changes, not necessarily through a deliberate manipulation. And it differs from a cross-sectional study, which looks at data at a single point in time to provide a snapshot rather than a time-based comparison or experimental manipulation. So the best match for a design that involves a comparison like an experiment but without random assignment is a quasi-experiment.

When a study compares outcomes after an intervention but does not randomize participants into treatment and control groups, that design is a quasi-experimental design. The strength is that it still borrows a causal question and includes a comparison, but the lack of random assignment means groups can differ in ways other than the intervention. Those preexisting differences can influence outcomes, so causal conclusions are weaker than in a true randomized controlled trial. Researchers often try to compensate with pretests, matching, or statistical controls to reduce bias, but the potential for selection differences remains.

This differs from a randomized controlled trial, which uses random assignment to create equivalent groups and bolster causal claims. It also differs from a longitudinal study, which follows the same individuals over time to observe changes, not necessarily through a deliberate manipulation. And it differs from a cross-sectional study, which looks at data at a single point in time to provide a snapshot rather than a time-based comparison or experimental manipulation.

So the best match for a design that involves a comparison like an experiment but without random assignment is a quasi-experiment.