Final answer:
Random assignment is used in a between-subjects experiment to minimize systematic differences between treatment groups and attribute differences observed to the independent variable. It helps control for lurking variables and increases internal validity.
Step-by-step explanation:
Random assignment is used in a between-subjects experiment to ensure that participants are assigned to treatments in a way that minimizes systematic differences between the groups. This is important because it allows researchers to attribute any differences observed between the groups to the manipulation of the independent variable, rather than preexisting differences. For example, if a researcher wants to test the effect of a new medication on a group of patients, random assignment helps ensure that both the treatment group and control group are similar in terms of factors like age, gender, and health conditions. By randomly assigning participants to treatments, random assignment helps to control for lurking variables and increases the internal validity of the experiment.