Araki 2014.

Study characteristics
Methods	Prospective, multicenter (13 institutions), observational cohort study. Study period: 2009 to 2010
Participants	Country: Japan. UC patients who underwent colorectal surgery
Interventions	1. Preoperative immunomodulator therapy (n= 92) 2. No preoperative immunomodulator (n= 103)
Outcomes	Superficial, deep and organ space surgical site infections within 30 days
Notes	NOS very high risk of bias overall
Risk of bias
Bias	Authors' judgement	Support for judgement
Representativeness of the exposed cohort	Low risk	All UC patients who underwent colorectal surgery from 2009 to 2010
Selection of the non exposed cohort	Low risk	Both groups obtained from the same hospitals and time period
Ascertainment of exposure	Low risk	Data collection prospectively on a standardized form by physicians
Demonstration that outcome of interest was not present at start of study	Unclear risk	No information was provided
Comparability of cohorts (Controlled for critical factor/other medications)	High risk	Univariate analysis
Comparability of cohorts (Controlled for additional factor)	High risk	Univariate analysis
Assessment of outcome	Low risk	Data collection prospectively on a standardized form by physicians
Was follow‐up long enough for outcomes to occur	Low risk	30 days
Adequacy of follow up of cohorts	Unclear risk	No information was provided