[Patient-centered evaluation of illness outcome in musculoskeletal diseases: selection and testing of outcome instruments].

Effectiveness research, economic evaluation, epidemiologic studies of disease consequences and clinical quality management all rely on standardized assessment of disease consequences with psychometrically sound questionnaires. For scientific, ethical and economical reasons, careful selection and evaluation of instruments is critical. Selection of instruments includes searches of medical databases (e.g. MEDLINE), testing of face-validity (does the instrument measure what we intend to measure?), and compatibility (is the instrument used internationally?). Evaluation of instruments includes the assessment of reliability, internal consistency and sensitivity. Most important is careful consideration of the practical usefulness (Interpretation of scores and scales, acceptance in the study population). Contact with instrument developers is advisable (Copyright issues, scoring, current version).