Standard error of measurement and smallest detectable change of the Sarcopenia Quality of Life (SarQoL) questionnaire: An analysis of subjects from 9 validation studies

• Published in: PloS one Vol. 14; no. 4; p. e0216065
• Main Authors: Geerinck, Anton, Alekna, Vidmantas, Beaudart, Charlotte, Bautmans, Ivan, Cooper, Cyrus, De Souza Orlandi, Fabiana, Konstantynowicz, Jerzy, Montero-Errasquín, Beatriz, Topinková, Eva, Tsekoura, Maria, Reginster, Jean-Yves, Bruyère, Olivier
• Format: Journal Article Web Resource
• Language: English
• Published: United States Public Library of Science 29.04.2019; Public Library of Science (PLoS)
• Subjects: Aged; Aged, 80 and over; Aging; Analysis; Biology and Life Sciences; Bone surgery; Change detection; Epidemiology; Error analysis; Error detection; Female; Fractures; Geriatrics; Gerontology; Health economics; Hospitals; Human health sciences; Humans; Male; Mathematical analysis; Medical research; Medicine; Medicine and Health Sciences; Middle Aged; Mortality; Musculoskeletal system; People and places; Public health; Public health, health care sciences & services; Quality of Life; Quantitative psychology; Research and Analysis Methods; Santé publique, services médicaux & soins de santé; Sarcopenia; Sarcopenia - pathology; Sciences de la santé humaine; Social Sciences; Standard error; Standard error of measurement; Surveys and Questionnaires; Systematic errors; Systematic review; Validation studies; Womens health; Working groups; Greece; Belgium
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0216065

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. 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. 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. 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".