OBJECTIVES: The Sarcopenia Quality of Life (SarQoL) questionnaire, a sarcopenia-specific patient-reported outcome measure, evaluates quality of life with 55 items. It produces 7 domain scores and 1 overall quality of life score, all between 0 and 100 points. This study aims to contribute to the interpretation of the SarQoL scores by calculating the standard error of measurement (SEM) and smallest detectable change (SDC) in a sample of subjects from 9 studies. METHODS: Subjects from 9 studies (conducted in Belgium, Brazil, Czech Republic, England, Greece, Lithuania, Poland and Spain) were included. The SEM, a measure of the error in the scores that is not due to true changes, was calculated by dividing the standard deviation of the difference between test and retest scores (SDdiff) by √2. The SDC, defined as change beyond measurement error, was calculated by multiplying SDdiff by 1.96. Bland-Altman plots were assessed for the presence of systematic errors. RESULTS: A total of 278 sarcopenic subjects, aged 77.67 ± 7.64 years and 61.5% women, were included. The SEM for the overall SarQoL score ranged from 0.18 to 4.20 points for the individual studies, and was 2.65 points when all subjects were analyzed together. The SDC for the overall score ranged from 0.49 to 11.65 points for the individual studies, and was 7.35 points for all subjects. The Bland-Altman plots revealed no systematic errors in the questionnaire. CONCLUSION: This study shows that, for individual subjects, a change in overall quality of life of at least 7.35 points (on a scale from 0 to 100) would have to be observed to confirm that a true change, beyond measurement error, has occurred. It also demonstrated that the SarQoL questionnaire is a precise instrument, with the observed scores within less than 3 points of the theoretical "true score".

Department of Geriatrics and Gerontology 1st Faculty of Medicine Charles University Prague Czech Republic

Department of Geriatrics University Hospital Ramón y Cajal Madrid Spain

Department of Gerontology Federal University of São Carlos São Carlos SP Brazil

Department of Pediatric Rheumatology Immunology and Metabolic Bone Diseases Medical University of Bialystok Bialystok Poland

Department of Physical Therapy School of Health and Welfare Technological Institute of Western Greece Aigio Greece

Faculty of Medicine Vilnius University Vilnius Lithuania

Frailty in Aging Research Group Vrije Universiteit Brussel Brussels Belgium

MRC Environmental Epidemiology Unit Southampton General Hospital Southampton United Kingdom

World Health Organization Collaborating Center for Public Health Aspects of Musculoskeletal Health and Ageing Department of Public Health Epidemiology and Health Economics University of Liège Liège Belgium

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