Why does random assignment matter?
Random assignment is an important part of control in experimental research, because it helps strengthen the internal validity of an experiment. In experiments, researchers manipulate an independent variable to assess its effect on a dependent variable, while controlling for other variables.
How are participants randomly assigned to different groups?
Participants are not randomly assigned to different groups, but instead assigned based on their characteristics. In this type of study, the characteristic of interest (e.g., gender) is an independent variable, and the groups differ based on the different levels (e.g., men, women, etc.).
Why do some research designs stratify subjects prior to random assignment?
Some research designs stratify subjects by geographic, demographic or other factors prior to random assignment in order to maximize the statistical power of the estimated effect of the treatment (e.g., GOTV intervention). Information about the randomization procedure is included in each experiment summary on the site.