Clinical overall score: outcome evaluation after lumbar disc surgery, assessments of reliability and validity

In previous studies assessing prognostic factors for the outcome of lumbar disc surgery, a Clinical Overall Score (COS) based on four subsets-pain intensity (VAS), physical signs, functional status (Oswestry) and analgesics--was used as the main outcome criterion. Both the patient's and the examiner's opinions of outcome and return to work were registered. In this paper, assessments are made of reliability and validity regarding the COS. The COS was found sensitive to changes, and internal consistency, assessed using Cronbach's alpha, Pearson's correlation analyses and factor analysis, was good. An interrater reliability study of the assessments of the physical signs, using weighted Kappa statistics, demonstrated fair to good levels of agreement for most of the signs. The concurrent validity of the COS was satisfactory; COS compared favourably with the patient's and with the examiner's opinion of outcome and return to work.