Predicting rehabilitation outcomes: The twisted pear revisited

Prediction of rehabilitation outcome occurs with few unifying theories or practices. The authors propose J. Fisher's (1959) neglected twisted pear model as central to understanding perplexing problems such as somatoform disorders, mild traumatic brain injury, likelihood of therapeutic benefit from rehabilitation interventions, and assessment of driving competence. Fisher argued that many psychological and biological behaviors were predictable in only one segment of the distribution. The 2 x 2 twisted pear matrix demonstrates this nonuniform scatter (heteroscedasticity), limiting acceptable classification accuracy to individuals with poor-impaired predictor scores. Outcomes become increasingly variable as scores improve to average or better. Examples from clinical practice support the conclusion that the twisted pear model is a useful paradigm for rehabilitation professionals. It's hard to make predictions, especially about the future.