design, experimental

n. A research strategy in which an experimenter systematically varies one or more independent variables while measuring one or more dependent variables, thus creating two or more distinct treatment conditions. There are two broad types of experimental designs:

• in the between-subjects or randomized groups design, different participants are randomly assigned to the different treatment conditions. For example, one group of depressed participants receives a drug and a separate group of participants receives a placebo pill instead of the drug (control group).
• in the within-subjects or repeated measures design, participants' behavior is measured across all treatment conditions. For example, each participant rates both neutral and smiling faces on physical attractiveness.

One alternative to the repeated measures design is the matched-subjects design. In this design, different groups of participants are matched on some variable believed to be relevant to the results of the study (e.g., intelligence).  

-KDM