Random Assignment

Random assignment is a term that is associated with true experiments (called controlled clinical trials in medical research) in which the effects of two or more "treatments" are compared with one another. Participants (respondents, subjects, etc.) are allocated to treatment conditions in such a way that each participant has the same chance of being a member of a particular treatment group. The groups so constituted are therefore as similar as possible at the beginning of the experiment before the treatments are introduced. If they differ at the end of the experiment, there will be a statistical basis for determining whether or not, or to what extent, it is the treatments that were the cause of the difference.

Traditionally, survey research and experimental research have not had ...