Which statement correctly differentiates experimental design from quasi-experimental design?

• A. Experimental design uses random assignment to conditions; quasi-experimental lacks random assignment.
• B. Quasi-experimental uses random assignment to conditions; experimental does not.
• C. Experimental designs require posttests only; quasi-experimental requires pretests.
• D. Quasi-experimental studies always include blinding of participants.

Answer: (A)

The essential distinction here is how participants are assigned to conditions. True experiments use random assignment, which helps ensure the groups are equivalent on average before the intervention. That equivalence makes it more likely that any differences observed after the intervention are caused by the manipulation itself, supporting stronger causal conclusions. Quasi-experimental designs lack random assignment, so groups may differ in important ways before the intervention, and those preexisting differences could explain post-intervention differences. The presence or absence of random assignment, not whether there are pretests or posttests, is what separates these designs. Blinding is not a defining feature either and can occur in various designs, but it doesn’t determine the core distinction.