Randomized single-subject experimental designs

Books on single-subject methodology tend to focus on traditional operant research techniques and thus provide little or no discussion of random introduction of treatments and statistical tests based on such randomization, i.e. randomization tests. Those books are the principal references to which researchers must turn for a comprehensive coverage of single-subject methodology, and so many researchers are likely to be unaware of the relevance of randomization (random assignment of treatment times to treatments) and randomization tests to single-subject experimentation. That is unfortunate because randomization is necessary in order to draw valid statistical inferences about treatment effects. The role of randomization in providing control over major threats to internal validity is explained in this article, and a number of randomized single-subject designs and their applications are provided. Appropriate rank tests are specified, and sources of free software for other, more complex, statistical tests are given.