What is the purpose of random assignment in experiments?

Random assignment is a crucial component in experimental research design, as it plays a significant role in eliminating bias and preexisting differences among participants. The primary aim of random assignment is to ensure that each participant has an equal chance of being placed in any of the experimental conditions. By randomly assigning participants, researchers can balance out variables, both known and unknown, across different groups. This means that potential confounding variables – whether they be age, gender, socioeconomic status, or any other characteristic – are distributed evenly among groups, thereby reducing the likelihood that these variables will influence the outcome of the study.

This process strengthens the internal validity of an experiment, allowing researchers to attribute any observed effects directly to the manipulation of the independent variable, rather than to other external factors. Consequently, random assignment helps to establish a causal relationship between variables, which is a primary goal in experimental research.