title: J-shapedness: an often missed, often miscalculated relation: the example of weight and mortality.
abstract: We present three considerations in analysing the association between weight and mortality, as well as other relations that might be non-linear in nature. First, authors must graphically plot their independent and dependent variables in a continuous manner. Second, authors should assess the shape of that relation, and note its shape. If it is non-linear, and specifically, J-shaped or U-shaped, careful consideration should be given to using the 'best' statistical model, of which multivariate fractional polynomial regression is a reasonable choice. Authors should also refrain from truncating their data to avoid dealing with non-linear relations.
authors.affiliation: Schulich School of Medicine and Dentistry, University of Western Ontario, London, Ontario, Canada.
authors.forename: Sissi
authors.initials: S
authors.lastname: Cao
authors.affiliation: Department of Family and Community Medicine and Institute for Clinical Evaluative Sciences, University of Toronto, Toronto, Canada.
authors.forename: Rahim
authors.initials: R
authors.lastname: Moineddin
authors.affiliation: Li Ka Shing Knowledge Institute, St. Michael's Hospital, Dalla Lana School of Public Health, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Marcelo L
authors.initials: ML
authors.lastname: Urquia
authors.affiliation: Division of General Internal Medicine, St. Michael's Hospital Scientist in the Keenan Research Centre, Li Ka Shing Knowledge Institute, St. Michael's Hospital Department of Medicine, University of Toronto Bell Fellow, Harvard Center for Population and Development Studies.
authors.forename: Fahad
authors.initials: F
authors.lastname: Razak
authors.affiliation: Departments of Medicine, Obstetrics & Gynecology and Health Policy Management & Evaluation, St. Michael's Hospital, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Joel G
authors.initials: JG
authors.lastname: Ray
mesh_terms: D001724:Birth Weight; D015992:Body Mass Index; D002423:Cause of Death; D003627:Data Interpretation, Statistical; D005260:Female; D006801:Humans; D008297:Male; D015233:Models, Statistical; D009765:Obesity / Q000401:mortality*; D050497:Stillbirth
keywords: Birth Weight; Clinical epidemiology; Epidemiology; Obesity; Perinatal Epidemiology