Kruis 1998.

Study characteristics
Methods	Multicenter, randomized, double‐blind, double‐dummy, parallel‐group study
Participants	Adults (18 to 75 years) with a mild‐to‐moderate (endoscopic score < 4) attack of ulcerative colitis (N = 168)
Interventions	Olsalazine 3 g/day (n = 88) or mesalazine (claversal) 3 g/day (n = 80) for 12 weeks
Outcomes	Primary outcome: Endoscopic remission (defined as a score of 0 or 1 on the Rachmilewitz index) Secondary outcomes: Clinical remission (< 1 on modified Rachmilewitz index), physician's global assessment on 4‐point scale
Notes	This study was supported by a grant from Pharmacia & Upjohn AB, Uppsala, Sweden Conflicts of interest were not reported
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Not described
Allocation concealment (selection bias)	Low risk	Centralized randomization
Blinding (performance bias and detection bias) All outcomes	Low risk	Double‐blind, double‐dummy
Incomplete outcome data (attrition bias) All outcomes	Low risk	25% dropout rate, but dropouts balanced across intervention groups with similar reasons for withdrawal
Selective reporting (reporting bias)	Low risk	Expected outcomes were reported
Other bias	Low risk	The study appears to be free of other sources of bias