Table 3.

Study quality

Study	Representativeness of study cohort	Ascertainment of intervention	Comparability of intervention and comparison/control group	Assessment of outcomes	Addressing incomplete data/quality of registry data	Missing data on primary interventions and outcomes/selection of patients
Register based studies
Chang 2002 [34]	?	?	?	+	?	+
Gutgesell 2002 [35]	?	?	?	+	?	+
Checchia 2005 [42]	?	+	?	+	?	-
Berry 2006 [33]	+	+	+	+	?	+
Hirsch 2008 [36]	+	+	?	+	?	+
Welke 2009 [23]	?	+	?	+	?	?
McHugh 2010 [40]	?	?	?	+	?	+
Hornik/Pasquali 2012 [37,38]	+	?	+	+	?	?
clinical studies
Karamlou 2010 [39]	?	+	?	+	?	?
Tabbutt 2012 [41]	?	+	?	?	?	?

+ Low risk of bias, - High risk of bias, ? Unclear risk of bias.