Imagine a factorial design in which there are two factors. Each factor has two levels. One factor is a between-groups factor (also known as an independent-groups factor or between-subjects factor) and the other is a within-groups factor (also known as a repeated-measures factor or within-subjects factor). If you wanted to have 40 participants in each cell of this design, how many unique participants would be needed for the study? Solution So When we are using between subejcts factor, different group of participants are used for each level of the factor and for within-subjects variable, testing is done on each participant at each level of the factor. Now we want 40 participants in each cells, this implies for between groups there would be a need of 40+40 different subjects and for within groups same set of 40 participants would be tested, hence we would need (40+40+40 = 120) unque participants..