Which design isolates cause by holding variables constant and randomizing participants to conditions?

Which design isolates cause by holding variables constant and randomizing participants to conditions?

• A. True experiment
• B. Quasi-experiment
• C. Observational study
• D. Case study

Answer: (A)

Manipulating the independent variable and randomly assigning participants to conditions is what lets researchers isolate causality. In a true experiment, the researcher actively changes the IV and uses randomization to create equivalent groups, while holding other variables constant or controlling them. This setup minimizes systematic differences between groups, so observed effects on the dependent variable can be attributed to the IV rather than to confounds. A quasi-experiment involves manipulation but uses nonrandom assignment, leaving room for preexisting differences between groups and weaker causal claims. An observational study records data without manipulation, making it difficult to rule out confounds. A case study investigates a single case or a small number of cases without randomization or control conditions, limiting causal inferences. Therefore, the design that best isolates cause through manipulation and randomization is the true experiment.

Manipulating the independent variable and randomly assigning participants to conditions is what lets researchers isolate causality. In a true experiment, the researcher actively changes the IV and uses randomization to create equivalent groups, while holding other variables constant or controlling them. This setup minimizes systematic differences between groups, so observed effects on the dependent variable can be attributed to the IV rather than to confounds. A quasi-experiment involves manipulation but uses nonrandom assignment, leaving room for preexisting differences between groups and weaker causal claims. An observational study records data without manipulation, making it difficult to rule out confounds. A case study investigates a single case or a small number of cases without randomization or control conditions, limiting causal inferences. Therefore, the design that best isolates cause through manipulation and randomization is the true experiment.