2. Risk of bias in studies arranged according to intervention and control.

Study name	Random sequence generation	Allocation concealment	Blinding of participants and health professionals	Blinding of outcome assessors	Incomplete outcome data bias	Selective outcome reporting	For‐profit bias	Other bias
In people who were eligible for surgery
Chen 2006	Low	Unclear	Unclear	Unclear	High	Low	Low	Low
Huang 2010	Unclear	Unclear	Unclear	Unclear	Unclear	Low	Low	Low
Fang 2014	Low	Low	High	High	Low	Low	Low	Low
Lee 2014	Unclear	Unclear	Unclear	Unclear	Unclear	Low	High	Low
In people who were not eligible for surgery
Bolondi 1996	Unclear	Unclear	Unclear	Unclear	Unclear	High	Unclear	Low
Koda 2001	Unclear	Unclear	Unclear	Unclear	Unclear	Low	Unclear	Low
Lin 2005	Low	Unclear	Unclear	Unclear	Low	Low	Unclear	Low
Orlacchio 2014	Low	Unclear	High	High	Low	Low	Low	Low
Costanzo 2015	Low	Unclear	High	High	Low	Low	Low	Low
Shibata 2002	Unclear	Unclear	Unclear	Unclear	Low	High	Unclear	Low
Lencioni 2003	Low	Unclear	Unclear	Unclear	High	Low	Unclear	Low
Shiina 2005	Low	Unclear	High	High	Low	Low	Unclear	Low
Brunello 2008	Low	Low	High	High	Low	Low	Low	Low
Giorgio 2011	Low	Low	Unclear	Low	Low	Low	Low	Low
Gan 2004	Unclear	Unclear	Unclear	Unclear	High	High	Unclear	Low
Chen 2005	Unclear	Unclear	Unclear	Unclear	Unclear	Low	Unclear	Low
Aikata 2006	Unclear	Unclear	Unclear	Unclear	Unclear	Low	Unclear	Low
El Kady 2013	Low	Unclear	Unclear	Unclear	Low	Low	Low	Low