Prognostic variability among chronic pain patients: implications for study design, interpretation, and reporting.

Chronic pain patients share many characteristics, but there is important prognostic variability among them. By selecting for certain characteristics, different recruitment methods and entry criteria for clinical or research programs may influence the likelihood of success regardless of treatment efficacy. This was demonstrated when subjects (n = 55) were recruited through lay publicity for a clinical trial of therapy for chronic back pain. In comparison to routine pain clinic patients (n=61), subjects in the clinical trial were better educated, were more often employed, had more favorable personality profiles, and were less likely to have had surgery or narcotic use (all p less than 0.004). Pain relief was significantly better for clinical trial subjects, apparently due to baseline prognostic differences rather than uniquely efficacious therapy. We conclude that chronic pain patients vary in prognostically important ways; that recruitment methods and criteria strongly influence these characteristics; and that greater attention to these details is needed when interpreting and reporting clinical research.