To make sure that groups of participants in an experiment are not generally different from each other before the experiment begins, the experimenter ____.
A) uses an objective observer to assign participants to groups
B) uses random assignment to assign participants to groups
C) assigns participants to groups by himself or herself without interference by anyone else
D) assigns participants to groups on the basis of an unimportant trait such as hair color

Question

Quizplus · Accepted Answer

Random assignment is the best method to ensure that groups of participants are not generally different from each other before the experiment begins. This ensures that any differences observed between groups are likely due to the independent variable being manipulated and not due to preexisting differences between groups. Objective observer and assigning participants by the experimenter without interference may introduce biases, and assigning participants based on an unimportant trait such as hair color is not a valid method for group assignment.

To Make Sure That Groups of Participants in an Experiment