Extensions of a versatile randomization test for assessing single-case intervention effects

The purpose of the present study was to investigate the statistical properties of two extensions of the Levin–Wampold (1999) single-case simultaneous start-point model's comparative effectiveness randomization test. The two extensions were (a) adapting the test to situations where there are more than two different intervention conditions and (b) examining the test's performance in classroom-based intervention situations, where the number of time periods (and associated outcome observations) is much smaller than in the contexts for which the test was originally developed. Various Monte Carlo sampling situations were investigated, including from one to five participant blocks per condition and differing numbers of time periods, potential intervention start points, degrees of within-phase autocorrelation, and effect sizes. For all situations, it was found that the Type I error probability of the randomization test was maintained at an acceptable level. With a few notable exceptions, respectable power was observed only in situations where the numbers of observations and potential intervention start points were relatively large, effect sizes were large, and the degree of within-phase autocorrelation was relatively low. It was concluded that the comparative effectiveness randomization test, with its desirable internal validity and statistical-conclusion validity features, is a versatile analytic tool that can be incorporated into a variety of single-case school psychology intervention research situations.