Introduction to four basic designs
The single-factor independent groups design refers to an experiment in which members of a sample of individuals are randomly allocated to various conditions. The design is known as the between-subjects design. This chapter introduces the repeated measures design can sometimes serve as an alternative to the single-factor independent groups design. The repeated-measures design is more powerful than the independent groups design, but it is often unusable because of problems arising from the need to obtain scores on the dependent variable several times on each subject. The blocking factor has the effect of making the scores of the subjects in any one group or cell more homogeneous, which in turn increases the power and sensitivity of the design. The advantage of the randomized block design is that it makes possible a more powerful or more sensitive test of a factor without sacrificing generalizability of the findings or economy.