The simplest of a between-subjects experimental design involves comparing only two groups of participants: the researcher manipulates one independent variable with only two levels. This design is often referred to as the single-factor two-group design or simply the two-group design. This type of design can be used to compare treatments, or to evaluate the effect of one treatment by comparing a treatment group and a control group. When the measurements consist of numerical scores, typically, a mean is computed for each group of participants, and then an independent-measures t tent is used to determine whether there is a significant difference between the means (sec Chapter 14).