Table 1.

Systematic review risk of bias assessment

Author	Adequate search	Risk of bias assessed	Quality score accounted for in analysis	Study details reported and differences accounted for	Statistical heterogeneity investigated	Gaps in research identified	Conclusions justified
Colorectal/colon surgery
Adamina et al6	✓	✓	UC	✓	UC	✓	✓
Ahmed et al7	✓	X	X	X	X	X	✓
Eskicioglu et al10	✓	✓	X	✓	✓	✓	✓
Gouvas et al11	✓	✓	X	✓	✓	✓	✓
Khan et al13	✓	✓	X	✓	X	✓	✓
Lv et al21	✓	✓	X	X	✓	✓	✓
Rawlinson et al15	✓	X	X	✓	UC	X	UC
Spanjersberg et al16	✓	✓	✓	✓	✓	✓	✓
Varadhan et al17	✓	✓	X	✓	✓	✓	✓
Walter et al18	✓	✓	✓	✓	✓	✓	✓
Wind et al19	✓	✓	✓	✓	✓	✓	✓
Gynaecological surgery
Lv et al20	✓	X	X	X	X	✓	✓
Liver/pancreatic surgery
Coolsen et al8	✓	✓	X	✓	X	✓	✓
Coolsen et al9 Link to66	✓	✓	✓	✓	✓	✓	✓
Hall et al12	X	X	X	✓	X	✓	✓
Various surgical specialities
Lemmens et al14	✓	X	X	✓	X	✓	✓
Sturm et al5	✓	X	X	✓	UC	✓	✓

UC, unclear reporting.