Nguyen 2014.

Study characteristics
Methods	Retrospective cohort. Study period: 2005 to 2012.
Participants	Country: Canada. CD and UC patients who underwent abdominal surgery in the ACS‐NSQIP database.
Interventions	1. Preoperative steroids (n= 6281) 2. No preoperative steroids (n= 9214)
Outcomes	Superficial and deep wound infection, intraabdominal infection, extraabdominal infection within 30 days of surgery
Notes	NOS very high risk of bias overall
Risk of bias
Bias	Authors' judgement	Support for judgement
Representativeness of the exposed cohort	Low risk	CD and UC patients who underwent abdominal surgery in the ACS‐NSQIP database from 2005 to 2012
Selection of the non exposed cohort	Low risk	Both groups obtained from the same database and time period
Ascertainment of exposure	Low risk	Patients identified by ICD‐9 codes
Demonstration that outcome of interest was not present at start of study	Unclear risk	Information not provided
Comparability of cohorts (Controlled for critical factor/other medications)	High risk	Did not control for other medications
Comparability of cohorts (Controlled for additional factor)	High risk	Did not control for additional factor
Assessment of outcome	Low risk	Obtained fron ACS‐NSQIP database
Was follow‐up long enough for outcomes to occur	Low risk	30 days
Adequacy of follow up of cohorts	Unclear risk	Information not provided