Table 2.

Characteristics of the 13 studies included.

Studies	Consecutive	Design	Pro-/retro-spective	Outcome	Selection bias	Information bias	Attrition bias	Verification bias
Li 2016	Yes	Cohort	Retrospective	EPL	Yes	No	No	NA
Liu 2015	Yes	Cohort	Retrospective	EPL	Yes	NA	No	NA
Romero 2015	Yes	Cohort	Prospective	EPL	Yes	No	No	NA
Cheng 2014	Yes	Cohort	Retrospective	EPL	Yes	Yes	No	NA
Angiolucci 2011	Yes	Cohort	Prospective	EPL	Yes	No	NA	NA
Ljunger 2010	Yes	Cohort	Prospective	EPL	Yes	NA	No	NA
Munoz 2010	Yes	Cohort	Prospective	EPL	NA	NA	NA	NA
Lathi 2007	Yes	Cohort	Retrospective	EPL	Yes	No	No	NA
Ginsberg 2001	Yes	Cohort	NA	EPL	Yes	Yes	NA	NA
Brajenovic 1998	Yes	Cohort	NA	EPL	NA	No	NA	NA
Coulam 1997	Yes	Cohort	NA	EPL	NA	No	NA	NA
Goldstein 1996 Dickey 1994	Yes	Cohort	Retrospective	EPL	Yes	NA	No	NA
	Yes	Cohort	Prospectively	EPL	Yes	No	No	NA