Statistical Analysis for Single-Case Designs

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Abstract
A recently developed statistical method for single-case subject designs based on classical test theory was used to examine the efficacy of imaginal exposure treatment for posttraumatic stress disorder (PTSD) in four Vietnam veterans. The method was sensitive to intraindividual changes across different outcome measures even when relatively few data points were available. Two veterans clearly improved from exposure and maintained their gains at 3-and 15-month follow-ups. One veteran improved marginally, whereas one veteran's symptoms worsened. Changes in heart rate monitored over the first two imaginal exposures indicated that veterans with greater heart-rate habituation responded better to exposure than did veterans with less or no habituation. The results suggest that the statistical method illustrated here has some advantages over other methods (e.g., visual inspection, time-series analysis) for examining clinical interventions in single-case designs.