What is required to establish causation in research?

• A. Large sample size
• B. Longitudinal design
• C. Random assignment
• D. Reproducible results

Answer: (C)

Establishing causation in research hinges on ruling out alternative explanations so that observed effects can be attributed to the manipulated variable. Random assignment is the tool that makes groups comparable on both measured and unmeasured characteristics, so any difference in outcomes is more plausibly caused by the intervention rather than preexisting differences. This creates internal validity and supports causal inferences.

A large sample size improves precision and statistical power, but it doesn’t by itself ensure that groups are equivalent or that the observed effect is truly caused by the manipulation. A longitudinal design helps establish that the cause precedes the effect, but without randomization, confounding variables can still cloud the relationship. Reproducible results demonstrate reliability but do not by themselves prove that one variable causes another.