What does random assignment help to achieve in experimental research?

Random assignment is a critical component of experimental research because it helps to minimize pre-existing differences among participants. By randomly assigning individuals to different experimental groups, researchers ensure that each group is likely to be similar in terms of demographics, characteristics, and potential confounding variables. This process enhances the internal validity of the study, as it reduces biases that could influence the outcomes of the experiment.

When participants are selected for different conditions through random assignment, it evens out differences that might otherwise skew results. For example, if one group were older or had different socio-economic statuses compared to another, these factors could explain the findings instead of the independent variable being tested. Thus, random assignment increases the likelihood that any observed effects can be attributed to the treatment or intervention rather than to inherent differences in the participants themselves.

This is why the choice highlighting the minimization of pre-existing differences among participants is the correct one, as it directly relates to the goal of achieving a more scientifically sound comparison between the groups being studied.