Evaluation of Criteria for Classical Dissociations in Single-Case Studies by Monte Carlo Simulation.

The conventional criteria for a classical dissociation in single-case studies require that a patient be impaired on one task and within normal limits on another. J. R. Crawford and P. H. Garthwaite (2005) proposed an additional criterion, namely, that the patient's (standardized) difference on the two tasks should differ from the distribution of differences in controls. Monte Carlo simulation was used to evaluate these criteria. When Type I errors were defined as falsely concluding that a control case exhibited a dissociation, error rates were high for the conventional criteria but low for Crawford and Garthwaite's criteria. When Type I error rates were defined as falsely concluding that a patient with equivalent deficits on the two tasks exhibited a dissociation, error rates were very high for the conventional criteria but acceptable for the latter criteria. These latter criteria were robust in the face of nonnormal control data. The power to detect classical dissociations was studied.