title: Selection bias in rheumatic disease research.
abstract: The identification of modifiable risk factors for the development of rheumatic conditions and their sequelae is crucial for reducing the substantial worldwide burden of these diseases. However, the validity of such research can be threatened by sources of bias, including confounding, measurement and selection biases. In this Review, we discuss potentially major issues of selection bias--a type of bias frequently overshadowed by other bias and feasibility issues, despite being equally or more problematic--in key areas of rheumatic disease research. We present index event bias (a type of selection bias) as one of the potentially unifying reasons behind some unexpected findings, such as the 'risk factor paradox'--a phenomenon exemplified by the discrepant effects of certain risk factors on the development versus the progression of osteoarthritis (OA) or rheumatoid arthritis (RA). We also discuss potential selection biases owing to differential loss to follow-up in RA and OA research, as well as those due to the depletion of susceptibles (prevalent user bias) and immortal time bias. The lesson remains that selection bias can be ubiquitous and, therefore, has the potential to lead the field astray. Thus, we conclude with suggestions to help investigators avoid such issues and limit the impact on future rheumatology research.
authors.affiliation: Section of Rheumatology and Clinical Epidemiology Research and Training Unit, Boston University School of Medicine, 650 Albany Street, Suite 200, Boston, MA 02118, USA.
authors.forename: Hyon K
authors.initials: HK
authors.lastname: Choi
authors.affiliation: Clinical Epidemiology Research and Training Unit, Boston University School of Medicine, 650 Albany Street, Suite 200, Boston, MA 02118, USA.
authors.forename: Uyen-Sa
authors.initials: US
authors.lastname: Nguyen
authors.affiliation: Clinical Epidemiology Research and Training Unit, Boston University School of Medicine, 650 Albany Street, Suite 200, Boston, MA 02118, USA.
authors.forename: Jingbo
authors.initials: J
authors.lastname: Niu
authors.affiliation: Department of Global Health and Population, Harvard School of Public Health, 665 Huntington Avenue, Building 1, Room 1107, Boston, MA 02115, USA.
authors.forename: Goodarz
authors.initials: G
authors.lastname: Danaei
authors.affiliation: Clinical Epidemiology Research and Training Unit, Boston University School of Medicine, 650 Albany Street, Suite 200, Boston, MA 02118, USA.
authors.forename: Yuqing
authors.initials: Y
authors.lastname: Zhang
mesh_terms: D001168:Arthritis; D001172:Arthritis, Rheumatoid / Q000503:physiopathology; D017281:Cost of Illness; D018450:Disease Progression; D006801:Humans; D010003:Osteoarthritis / Q000503:physiopathology; D012216:Rheumatic Diseases / Q000453:epidemiology*; D012307:Risk Factors; D015983:Selection Bias; D013997:Time Factors