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 Sissi Cao
A1 Rahim Moineddin
A1 Marcelo L Urquia
A1 Fahad Razak
A1 Joel G Ray
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.