In experimental design, selecting people with similar characteristics and splitting into experimental vs control groups describes which design?

• A. Classic design
• B. Randomized block design
• C. Factorial design
• D. Quasi-experiment

Answer: (A)

The main idea here is creating comparable groups and measuring the effect of an intervention by random assignment. In a classic experimental design, you start with participants who are similar on key characteristics to reduce baseline differences. Then you randomly assign them to an experimental group (which receives the treatment) and a control group (which does not). This random allocation helps ensure that any differences observed after the intervention are due to the treatment itself rather than preexisting differences between participants, strengthening internal validity. If you were explicitly forming blocks of similar participants and randomizing within each block, that would describe a randomized block design. A factorial design would involve more than one treatment factor and their interactions, and a quasi-experiment lacks random assignment.