RT Journal Article SR Electronic T1 J-shapedness: an often missed, often miscalculated relation: the example of weight and mortality JF Journal of Epidemiology and Community Health JO J Epidemiol Community Health FD BMJ Publishing Group Ltd SP 683 OP 690 DO 10.1136/jech-2013-203439 VO 68 IS 7 A1 Cao, Sissi A1 Moineddin, Rahim A1 Urquia, Marcelo L A1 Razak, Fahad A1 Ray, Joel G YR 2014 UL http://jech.bmj.com/content/68/7/683.abstract AB 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.