Outcome assessment in low back pain: how low can you go?

The present study examined the psychometric characteristics of a "core-set'' of six individual questions ( on pain, function, symptom-specific well-being, work disability, social disability and satisfaction) for use in low back pain (LBP) outcome assessment. A questionnaire booklet was administered to 277 German-speaking LBP patients with a range of common diagnoses, before and 6 months after surgical (N = 187) or conservative (N = 90) treatment. The core-set items were embedded in the booklet alongside validated 'reference' questionnaires: Likert scales for back/leg pain; Roland and Morris disability scale; WHO Quality of Life scale; Psychological General Well-Being Index. A further 45 patients with chronic LBP completed the booklet twice in 1 - 2 weeks. The minimal reliability ( similar to Cronbach's alpha) for each core item was 0.42 - 0.78, increasing to 0.84 for a composite index score comprising all items plus an additional question on general well-being ('quality of life'). Floor or ceiling effects of 20 - 50% were observed for some items before surgery ( function, symptom-specific well-being) and some items after it ( disability, function). The intraclass correlation coefficient (ICC) ("test - retest reliability'') was moderate to excellent (ICC, 0.67 - 0.95) for the individual core items and excellent ( ICC, 0.91) for the composite index score. With the exception of "symptom- specific well-being'', the correlations between each core item and its corresponding reference questionnaire ("validity'') were between 0.61 and 0.79. Both the composite index and the individual items differentiated ( P< 0.001) between the severity of the back problem in surgical and conservative patients ( validity). The composite index score had an effect size ( sensitivity to change) of 0.95, which was larger than most of the reference questionnaires (0.47 - 1.01); for individual core items, the effect sizes were 0.52 - 0.87. The core items provide a simple, practical, reliable, valid and sensitive assessment of outcome in LBP patients. We recommend the widespread and consistent use of the core-set items and their composite score index to promote standardisation of outcome measurements in clinical trials, multicentre studies, routine quality management and surgical registry systems.