Random assignment of participants to conditions and control over confounding variables are two reasons why experimental methods can evaluate causal relationships.

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Random assignment helps ensure that any differences between and within the groups are not systematic at the outset of the experiment, thereby allowing any differences observed at the end of the experiment to be attributed to the experimental manipulations rather than to pre-existing differences. Control over confounding variables means that the researcher can isolate the effect of the independent variable on the dependent variable, thereby providing a clearer test of causality.

Random Assignment of Participants to Conditions and Control Over Confounding