Statistical Analysis of Single-Subject Designs

Abstract

To the Editor: The application of statistical analysis to single-subject designs is controversial and not straightforward. For this reason, we read the article by Nourbakhsh and Ottenbacher1 in the August 1994 issue of Physical Therapy with interest. The purposes of the study were to examine whether the use of different statistical analysis methods would lead to different statistical conclusions and to identify factors of graphed data that might have effected any observed difference in the statistical conclusions. The three methods studied were the C statistic,2 the two-standard deviation band method,3 and the split-middle method of trend estimation.4 To investigate the first purpose, the method of investigation was to analyze data from 42 AB graphs and to compare the statistical conclusions. The authors' methodological procedures for comparing the three techniques for agreement in statistical conclusions were limited and not entirely appropriate, for the following reasons:… [ ARTICLE][1] [1]: /lookup/volpage/74/768?iss=8