Table 2.

Risk of bias for cohort trails

Study	Selection				Comparability	outcome			Score
	Represent-ativeness of the exposed cohort	Selection of the non-exposed cohort	Ascertainment of exposure	Demonstration that outcome of interest was not present at start of study	Comparabili-ty of Cohorts on the Basis of the Design or Analysis	Assess-ment of outco-me	Was follow-up long enough for outcomes to occur	Adequacy of follow -up of cohorts
Beloosesky 2002 [26]	★	★	★	★		★		★	6
Bliemel 2015 [27]	★	★	★	★	★	★	★	★	8
Brouquet 2010 [25]	★	★	★	★		★	★	★	7
Guo 2014 [29]	★	★	★	★	★	★	★	★	8
Häkkinen 2007 [28]	★	★	★	★	★	★	★	★	8
Huusko 2000 [19]	★	★	★	★	★	★	★	★	8
Jones 2017 [31]	★	★	★	★		★	★	★	7
Kalisvaart 2006 [30]		★	★	★	★	★		★	6
Karni 2013 [33]	★	★	★	★		★	★	★	7
Kratz 2015 [32]	★	★	★		★		★	★	6
Lee 2016 [7]	★	★	★	★		★	★	★	7
Moncada 2005 [35]	★	★	★	★	★	★		★	7
Morghen 2011 [34]	★	★	★	★	★	★	★	★	8
Osse 2012 [36]	★	★	★	★		★	★	★	7
Otano 2015 [38]	★	★	★	★	★	★	★	★	8
Reissmüller 2006 [37]	★	★	★	★		★	★	★	7
Rolland 2004 [22]	★	★	★	★	★	★	★	★	8
Ruggiero 2016 [21]	★	★	★	★		★	★	★	7
Schaller2012 [23]	★	★	★	★	★	★	★	★	8
Witlox 2009 [24]	★	★	★	★		★	★	★	7
Yukako 2016 [20]	★	★	★			★	★	★	6