title: Minimal Clinically Important Difference as Applied in Rheumatology: An OMERACT Rasch Working Group Systematic Review and Critique.
abstract: OBJECTIVE
  We aimed to evaluate how minimal (clinically) important differences (MCID/MID) were calculated in rheumatology in the past 2 decades and demonstrate how the calculation is compromised by the lack of interval scaling.
  
  
  METHODS
  We conducted a systematic literature review on articles reporting MCID calculation in osteoarthritis (OA) and rheumatoid arthritis (RA) from January 1, 1989, to May 9, 2014. We evaluated the methods of MCID calculation and recorded the ranges of MCID for common patient-reported outcome measures (PROM). Taking data from the Health Assessment Questionnaire (HAQ), we showed the effects of performing mathematical calculations on ordinal data.
  
  
  RESULTS
  A total of 330 abstracts were reviewed and 123 articles chosen for full text review. Thirty-six (19 OA, 16 RA and 1 OA-RA) articles were included in the final evaluation. The Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) was the most frequently reported PROM with relevant calculations in OA, and the HAQ in RA. Sixteen articles used anchor-based methods alone for calculation of MCID, and 1 article used distribution-based methods alone. Nineteen articles used both anchor and distribution-based methods. Only 1 article calculated MCID using an interval scale. Wide ranges in MCID for the WOMAC in OA and HAQ in RA were noted. Ordinal-based derivations of MCID are shown to understate true change at the margins, and overstate change in the mid-range of a scale.
  
  
  CONCLUSIONS
  The anchor-based method is commonly used in the calculation of MCID. However, the lack of interval scaling is shown to compromise validity of MCID calculation.
authors.affiliation: From the Ankara University Faculty of Medicine, Department of Biostatistics, Ankara, Turkey; Department of Rheumatology and Immunology, Singapore General Hospital, Singapore; Duke-NUS Graduate Medical School, Singapore; Department of Internal Medicine II, Rheumatology, Clinical Immunology, Osteology, Physical Therapy, and Sports Medicine, Schlosspark-Klinik, Teaching Hospital of the Charité, University Medicine Berlin, Berlin, Germany; Swiss Paraplegic Research, Nottwil, Switzerland; Leeds Institute of Rheumatic and Musculoskeletal Medicine, University of Leeds and UK National Institute for Health Research Leeds Musculoskeletal Biomedical Research Unit, Leeds, UK.B. Doganay Erdogan, PhD, Assistant Professor, Ankara University Faculty of Medicine, Department of Biostatistics; Y.Y. Leung, MD, Assistant Professor, Duke-NUS Graduate Medical School, Singapore; C. Pohl, MD, Department of Internal Medicine II, Rheumatology, Clinical Immunology, Osteology, Physical Therapy and Sports Medicine, Schlosspark-Klinik, Teaching Hospital of the Charité, University Medicine Berlin; A. Tennant, PhD, MD, Scientific Adviser, Swiss Paraplegic Research; P.G. Conaghan, MBBS, PhD, FRACP, FRCP, Professor of Musculoskeletal Medicine, Leeds Institute of Rheumatic and Musculoskeletal Medicine. beyzadoganay@gmail.com.
authors.forename: Beyza
authors.initials: B
authors.lastname: Doganay Erdogan
authors.affiliation: From the Ankara University Faculty of Medicine, Department of Biostatistics, Ankara, Turkey; Department of Rheumatology and Immunology, Singapore General Hospital, Singapore; Duke-NUS Graduate Medical School, Singapore; Department of Internal Medicine II, Rheumatology, Clinical Immunology, Osteology, Physical Therapy, and Sports Medicine, Schlosspark-Klinik, Teaching Hospital of the Charité, University Medicine Berlin, Berlin, Germany; Swiss Paraplegic Research, Nottwil, Switzerland; Leeds Institute of Rheumatic and Musculoskeletal Medicine, University of Leeds and UK National Institute for Health Research Leeds Musculoskeletal Biomedical Research Unit, Leeds, UK.B. Doganay Erdogan, PhD, Assistant Professor, Ankara University Faculty of Medicine, Department of Biostatistics; Y.Y. Leung, MD, Assistant Professor, Duke-NUS Graduate Medical School, Singapore; C. Pohl, MD, Department of Internal Medicine II, Rheumatology, Clinical Immunology, Osteology, Physical Therapy and Sports Medicine, Schlosspark-Klinik, Teaching Hospital of the Charité, University Medicine Berlin; A. Tennant, PhD, MD, Scientific Adviser, Swiss Paraplegic Research; P.G. Conaghan, MBBS, PhD, FRACP, FRCP, Professor of Musculoskeletal Medicine, Leeds Institute of Rheumatic and Musculoskeletal Medicine.
authors.forename: Ying Ying
authors.initials: YY
authors.lastname: Leung
authors.affiliation: From the Ankara University Faculty of Medicine, Department of Biostatistics, Ankara, Turkey; Department of Rheumatology and Immunology, Singapore General Hospital, Singapore; Duke-NUS Graduate Medical School, Singapore; Department of Internal Medicine II, Rheumatology, Clinical Immunology, Osteology, Physical Therapy, and Sports Medicine, Schlosspark-Klinik, Teaching Hospital of the Charité, University Medicine Berlin, Berlin, Germany; Swiss Paraplegic Research, Nottwil, Switzerland; Leeds Institute of Rheumatic and Musculoskeletal Medicine, University of Leeds and UK National Institute for Health Research Leeds Musculoskeletal Biomedical Research Unit, Leeds, UK.B. Doganay Erdogan, PhD, Assistant Professor, Ankara University Faculty of Medicine, Department of Biostatistics; Y.Y. Leung, MD, Assistant Professor, Duke-NUS Graduate Medical School, Singapore; C. Pohl, MD, Department of Internal Medicine II, Rheumatology, Clinical Immunology, Osteology, Physical Therapy and Sports Medicine, Schlosspark-Klinik, Teaching Hospital of the Charité, University Medicine Berlin; A. Tennant, PhD, MD, Scientific Adviser, Swiss Paraplegic Research; P.G. Conaghan, MBBS, PhD, FRACP, FRCP, Professor of Musculoskeletal Medicine, Leeds Institute of Rheumatic and Musculoskeletal Medicine.
authors.forename: Christoph
authors.initials: C
authors.lastname: Pohl
authors.affiliation: From the Ankara University Faculty of Medicine, Department of Biostatistics, Ankara, Turkey; Department of Rheumatology and Immunology, Singapore General Hospital, Singapore; Duke-NUS Graduate Medical School, Singapore; Department of Internal Medicine II, Rheumatology, Clinical Immunology, Osteology, Physical Therapy, and Sports Medicine, Schlosspark-Klinik, Teaching Hospital of the Charité, University Medicine Berlin, Berlin, Germany; Swiss Paraplegic Research, Nottwil, Switzerland; Leeds Institute of Rheumatic and Musculoskeletal Medicine, University of Leeds and UK National Institute for Health Research Leeds Musculoskeletal Biomedical Research Unit, Leeds, UK.B. Doganay Erdogan, PhD, Assistant Professor, Ankara University Faculty of Medicine, Department of Biostatistics; Y.Y. Leung, MD, Assistant Professor, Duke-NUS Graduate Medical School, Singapore; C. Pohl, MD, Department of Internal Medicine II, Rheumatology, Clinical Immunology, Osteology, Physical Therapy and Sports Medicine, Schlosspark-Klinik, Teaching Hospital of the Charité, University Medicine Berlin; A. Tennant, PhD, MD, Scientific Adviser, Swiss Paraplegic Research; P.G. Conaghan, MBBS, PhD, FRACP, FRCP, Professor of Musculoskeletal Medicine, Leeds Institute of Rheumatic and Musculoskeletal Medicine.
authors.forename: Alan
authors.initials: A
authors.lastname: Tennant
authors.affiliation: From the Ankara University Faculty of Medicine, Department of Biostatistics, Ankara, Turkey; Department of Rheumatology and Immunology, Singapore General Hospital, Singapore; Duke-NUS Graduate Medical School, Singapore; Department of Internal Medicine II, Rheumatology, Clinical Immunology, Osteology, Physical Therapy, and Sports Medicine, Schlosspark-Klinik, Teaching Hospital of the Charité, University Medicine Berlin, Berlin, Germany; Swiss Paraplegic Research, Nottwil, Switzerland; Leeds Institute of Rheumatic and Musculoskeletal Medicine, University of Leeds and UK National Institute for Health Research Leeds Musculoskeletal Biomedical Research Unit, Leeds, UK.B. Doganay Erdogan, PhD, Assistant Professor, Ankara University Faculty of Medicine, Department of Biostatistics; Y.Y. Leung, MD, Assistant Professor, Duke-NUS Graduate Medical School, Singapore; C. Pohl, MD, Department of Internal Medicine II, Rheumatology, Clinical Immunology, Osteology, Physical Therapy and Sports Medicine, Schlosspark-Klinik, Teaching Hospital of the Charité, University Medicine Berlin; A. Tennant, PhD, MD, Scientific Adviser, Swiss Paraplegic Research; P.G. Conaghan, MBBS, PhD, FRACP, FRCP, Professor of Musculoskeletal Medicine, Leeds Institute of Rheumatic and Musculoskeletal Medicine.
authors.forename: Philip G
authors.initials: PG
authors.lastname: Conaghan
mesh_terms: D001172:Arthritis, Rheumatoid / Q000175:diagnosis* / Q000628:therapy; D003245:Consensus Statements as Topic; D004185:Disability Evaluation; D018450:Disease Progression; D005260:Female; D006801:Humans; D008297:Male; D010003:Osteoarthritis / Q000175:diagnosis* / Q000628:therapy; D010147:Pain Measurement; D017060:Patient Satisfaction / Q000706:statistics & numerical data*; D017410:Practice Guidelines as Topic / Q000592:standards; D011788:Quality of Life; D016059:Range of Motion, Articular / Q000502:physiology; D012219:Rheumatology / Q000592:standards; D018570:Risk Assessment; D012680:Sensitivity and Specificity; D012720:Severity of Illness Index
keywords: ANCHOR-BASED APPROACHES; DISTRIBUTION-BASED APPROACHES; MINIMAL CLINICALLY IMPORTANT DIFFERENCE; OSTEOARTHRITIS; PATIENT-REPORTED OUTCOME MEASURES; RHEUMATOID ARTHRITIS