Experimental Designs

Experimental designs are used to examine the effect of a treatment or intervention on some outcome. In the simplest two-group case, a treatment is implemented with one group of participants (the treatment group) and not with another (the control group). Experiments can be conducted with individual participants or with clusters of individuals. That is, the unit of assignment may be at the individual level or at the cluster level. This entry refers to individual participants as the unit of assignment with the understanding that the same designs may be used with clusters of individuals. The entry further describes experimental designs, looks at the role of randomization in experimental designs, and discusses some commonly used experimental designs.

Experimental designs require that the researcher assign participants to the ...