Bio-medicine and the Rehabilitation Scientific Model : Rasch Measurement

\u201cHard\u201d sciences based on \u201cobjective\u201d measurements such as chemistry and physics provide the backbone of Bio-medicine. This explores and strives to repair body parts (ranging from organs to molecules) \u201cfrom inside\u201d. \u201cWhole-person\u201d phenomena (behaviours) such as walking, speaking, suffering pain, being dependent on another one\u2019s help cannot be ascribed to any parts of the person. Behaviours can only be observed \u201cfrom outside\u201d. Raters can only approach at large a linear continuous measure by assigning \u201csubjective\u201d discontinuous scores (yes/no, 0/1) to items/questions in questionnaires. Questionnaires are the basis for measurement in \u201csoft\u201d sciences\u201d such as Psychology and Sociology. Is Rehabilitation outside the mainstream of bio-medical research? Behavioural outcomes are the core business of Rehabilitation which, in fact, used massively the questionnaires. In the meanwhile, Rehabilitation is deeply rooted within biomedical sciences. It tended to consider questionnaires as a secondary issue, not worth of any specific scientific efforts. The statistical model proposed in 1960 by Georg Rasch (died 1980) provided a formal and general solution to most of the weaknesses of raw scores. Since 1989, Rasch modelling was more and more adopted in Rehabilitation: a) to re-validate and improve existing questionnaires (e.g. Functional Independence Measure and Dizziness Handicap Inventory); b) to build up new questionnaires focussed on established variables (e.g. EquiScale for balance); c) to outline new variables (e.g. BACKILL for back syndromes; LAPMER for disability in profound mental retardation; ABILHAND for manual ability in Stroke and Rheumatoid Arthritis; SCIM for disability in spinal lesions; Work Instability Scale for unemployment risk in disabled people); e) to equate questionnaires tackling the same construct across different languages and cultures (e.g. the PRO-ESOR european study); f) to build-up quality checks of outcome measures adopted for financial and management purposes (e.g. the FIM-based inpatient classification system in Italy). Indeed, Rasch analysis is now reinforcing the \u201csoft\u201d side of Rehabilitation research. References: \u2022 Andrich D. \u2018Rasch models for measurement.\u2019 1998. Sage Publications, Newbury Park. \u2022 Gray ML, Bonventre JV. Training PhD researchers to translate science to clinical medicine: closing the gap from the other side. Nature Medicine 2002;8:433-43. \u2022 Kuhn TS. The structure of scientific revolution. The University of Chicago Press 1970 (original edition 1962). \u2022 Tesio L. Measuring person\u2019s behaviours and perceptions: Rasch analysis as a tool for rehabilitation research. Journal of Rehabilitation Medicine 2003;35:105-115. \u2022 Tesio L. Measurement in clinical vs. biological medicine. The Rasch model as a bridge over a widening gap. J Appl Meas 2004, submitted. \u2022 Wright B, Linacre JM. Observations are always ordinal: measurement, however, must be interval. Arch Phys Med Rehabil 1989;70,12:857-86