What does random assignment aim to achieve in research studies?

Random assignment is a critical procedure in research studies designed to enhance the internal validity of the findings. The primary goal of random assignment is to allocate subjects to different groups—such as treatment and control groups—in a random manner. This randomness ensures that each participant has an equal chance of being placed in any group, which helps to evenly distribute any confounding variables across those groups.

By reducing systemic differences between the groups, random assignment minimizes the potential for selection bias. This means that differences observed in outcomes can be more confidently attributed to the treatment or intervention being studied, rather than to pre-existing differences among participants. Therefore, it helps researchers draw more robust conclusions about the effects of the interventions being evaluated.

In contrast, ensuring all subjects receive the same treatment does not pertain to the randomness of group assignment; rather, it relates to standardizing treatment. Minimizing researcher bias is an important aspect of maintaining objectivity, but it is not directly the aim of random assignment itself. Selecting participants based on their previous experiences does not relate to the concept of random assignment, as it would introduce biases rather than mitigate them. Thus, the essence of random assignment lies in its ability to allocate subjects randomly to reduce bias in the comparison between groups.