Research participants are randomly assigned to different groups in an experiment in order to

In any experimentation, involvement of participant is for experimental trial for studying the larger population as subject of experiment. Studying and research is done the participant.

Random distribution of these members into groups is done as they are representing the population and randomness can define the general and actual phenomena while experiment and obtaining results.

Randomly assigning the group is done to decrease the chances of already present differences in the cluster of participant while conduction of experiment.