A Scale for Predicting Nonphysiological Contributions to Pain

Background: Waddell and colleagues have identified a series of nonorganic signs which may appear in low back pain patients. The occurrence of these signs helps predict nonphysiological factors in the etiology of the pain. This study describes the development of the Waddell Equivalency Scale (WES) which elicits comparable information from patients with pain at other sites. Methods: One hundred fifty patients presenting to a comprehensive pain clinic with low back pain were evaluated by physicians for Waddell signs and by psychologists using the Pain Presentation Inventory (PPI) developed by Psychometric Designs Inc. From three scales of the PPI, correlation, analysis of variance and multiple regression identified a formula which predicted Waddell signs from the PPI. The study was replicated on a new sample of 150 patients with almost identical results. The two samples were combined, again with highly similar results. An interpretive scheme was devised for use of the WES scale. Results: The WES score derived from three scales of the PPI predicts the number of Waddell signs elicited from low back pain patients. Since it comes from a paper-and-pencil test rather than a physical examination, it can be used with patients whose pain locus is other than the back. Conclusions: Behavioral expectations and treatment plans, à la Waddell, can now be applied to patients with other than low back pain. Clinical application of the WES information over a variety of pain populations will be required to determine the parameters of its usefulness.