STROBE Statement—Checklist of items that should be included in reports of cohort studies

	Item No	Recommendation
Title and abstract	1	(a) Indicate the study’s design with a commonly used term in the title or the abstract Listed in line 2
		(b) Provide in the abstract an informative and balanced summary of what was done and what was found This is provided – lines 27-45
Introduction
Background/rationale	2	Explain the scientific background and rationale for the investigation being reported This is provided – lines 52-99
Objectives	3	State specific objectives, including any prespecified hypotheses This is provided – lines 92-99
Methods
Study design	4	Present key elements of study design early in the paper This is provided – lines 100-142
Setting	5	Describe the setting, locations, and relevant dates, including periods of recruitment, exposure, follow-up, and data collection This is provided – lines 101-118
Participants	6	(a) Give the eligibility criteria, and the sources and methods of selection of participants. Describe methods of follow-up This is provided – lines 101-118
		(b) For matched studies, give matching criteria and number of exposed and unexposed
Variables	7	Clearly define all outcomes, exposures, predictors, potential confounders, and effect modifiers. Give diagnostic criteria, if applicable This is provided – lines 127-134
Data sources/measurement	8*	For each variable of interest, give sources of data and details of methods of assessment (measurement). Describe comparability of assessment methods if there is more than one group This is provided – lines 127-134
Bias	9	Describe any efforts to address potential sources of bias This is provided – lines 100-142 and in discussion lines 236-244
Study size	10	Explain how the study size was arrived at This study included all patients that were started on dual biologic therapy in the study inclusion dates.
Quantitative variables	11	Explain how quantitative variables were handled in the analyses. If applicable, describe which groupings were chosen and why This is provided – lines 135-139
Statistical methods	12	The below are addressed in lines 135-139 (a) Describe all statistical methods, including those used to control for confounding
		(b) Describe any methods used to examine subgroups and interactions
		(c) Explain how missing data were addressed
		(d) If applicable, explain how loss to follow-up was addressed
		(e) Describe any sensitivity analyses
Results
Participants	13*	(a) Report numbers of individuals at each stage of study—eg numbers potentially eligible, examined for eligibility, confirmed eligible, included in the study, completing follow-up, and analysed This is provided – lines 145-171 and 184-186
		(b) Give reasons for non-participation at each stage N/A
		(c) Consider use of a flow diagram
Descriptive data	14*	(a) Give characteristics of study participants (eg demographic, clinical, social) and information on exposures and potential confounders This is provided – lines 146-163 and Table 1
		(b) Indicate number of participants with missing data for each variable of interest This is described in Tables 3 and 4: † PRO-2 unable to be calculated in two trials due to presence of an ostomy. ‡ Endoscopic endpoint data not yet available in four trials; three were considered failure of DBT due to surgery or entering a clinical trial - one was awaiting follow-up but achieved clinical response.
		(c) Summarise follow-up time (eg, average and total amount) This is provided – lines 184-186
Outcome data	15*	Report numbers of outcome events or summary measures over time This is provided – lines 172-201
Main results	16	The below are provided in lines 144-208 (a) Give unadjusted estimates and, if applicable, confounder-adjusted estimates and their precision (eg, 95% confidence interval). Make clear which confounders were adjusted for and why they were included
		(b) Report category boundaries when continuous variables were categorized
		(c) If relevant, consider translating estimates of relative risk into absolute risk for a meaningful time period
Other analyses	17	Report other analyses done—eg analyses of subgroups and interactions, and sensitivity analyses N/A
Discussion
Key results	18	Summarise key results with reference to study objectives This is provided – lines 211-220
Limitations	19	Discuss limitations of the study, taking into account sources of potential bias or imprecision. Discuss both direction and magnitude of any potential bias This is provided – lines 236-244
Interpretation	20	Give a cautious overall interpretation of results considering objectives, limitations, multiplicity of analyses, results from similar studies, and other relevant evidence This is provided – lines 245-259
Generalisability	21	Discuss the generalisability (external validity) of the study results This is provided – lines 256-259
Other information
Funding	22	Give the source of funding and the role of the funders for the present study and, if applicable, for the original study on which the present article is based This is provided – lines 328-373