Final answer:
Random assignment in an experiment means that subjects are placed in two groups randomly, ensuring no systematic differences between the groups before the experiment begins.
Step-by-step explanation:
Random assignment is a crucial step in experimental design. When a researcher randomly assigns subjects to two groups at the beginning of an experiment, it means that each subject has an equal chance of being placed in either the experimental or control group. This random assignment helps to ensure that there are no systematic differences between the groups before the experiment begins. By doing this, any differences observed between the groups can be attributed to the manipulation of the independent variable, rather than preexisting differences.