In Methods of Randomization in Experimental Design, author Valentim R. Alferes presents the main procedures of random assignment and local control in between-subjects experimental designs and the counterbalancing schemes in within-subjects or cross-over experimental designs. Alferes uses a pedagogical strategy that allows the reader to implement all randomization methods by relying on the materials given in the appendices and using common features included in most word processor software.

A companion website at provides downloadable IBM SPSS and R versions of SCRAED, a package that performs simple and complex random assignment in experimental design, including the 18 randomization methods presented in Chapters 2 and 3.

Within-Subjects Designs Randomization

3.1 Basic Assumptions and Specific Threats to Validity

A within-subjects design is an experimental design in which two or more units (subjects) are exposed to two or more treatment levels (or treatment level combinations) over two or more periods and outcome measures are recorded after each exposure. As such, within-subjects designs contrast with between-subjects designs, wherein each experimental unit is only exposed to one treatment level (or treatment level combination). Figure 3.1 outlines a within-subjects design in which every experimental unit receives three treatment levels (A, B, and C, not necessarily in this order) in three consecutive periods (Periods 1, 2, and 3). Briefly stated, within-subjects designs concern experimental situations “where a number of subjects … receive a sequence of treatments over a ...

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