Table 2.

Risk of bias of the included studies judged by the review authors

First author, publication year	Random sequence generation	Allocation concealment	Blinding of participants	Blinding of outcome assessment	Duration
Aurilio 2009	Unclear	High	Unclear	Unclear	Unclear
Bohme 2003	Unclear	Unclear	Low	Low	Unclear
Bono 1997	Low	Unclear	Low	Unclear	Unclear
Brema 1996	Unclear	Unclear	Unclear	Unclear	Low
De Conno 1987	Unclear	Unclear	Unclear	Unclear	Unclear
Dini 1986	Unclear	Unclear	Low	Unclear	Unclear
Kjaer 1982	Unclear	High	Unclear	Low	Unclear
Likar 2007	Unclear	Low	High	High	Low
Noda 1989	Unclear	Unclear	Unclear	Unclear	High
Pace 2007	Low	Unclear	Unclear	Unclear	Unclear
Poulain 2008	Low	Low	Low	Unclear	Unclear
Sittl 2003	Unclear	Unclear	Unclear	Unclear	High
Sorge 2004	Low	High	High	Unclear	Unclear
Taguchi 1982	Unclear	Unclear	Low	Unclear	Unclear
Ventafridda 1983	Unclear	Unclear	Unclear	Unclear	Unclear
Wirz 2009	Low	Unclear	High	High	High

Low: low risk of bias; high: high risk of bias; Unclear: Unclear risk of bias.