bb‐Baron 2005.

Study characteristics
Methods	Case control study ‐ to examine environmental risk factors prior to the development of inflammatory bowel disease in a paediatric population‐based case‐control study
Participants	This was a population‐based matched case‐control study. Cases were all patients from the EPIMAD registry (registry of IBD in Northern France since 1988) who had a diagnosis of either CD or UC between January 1988 and December 1997 and were less than 17 years old at the time of IBD diagnosis. Controls were randomly selected from telephone number lists (random‐digit dialling) and matched 1:1 to each case by age (2 years), sex, and living area (region). A total of 222 incident cases of Crohn’s disease and 60 incident cases of ulcerative colitis occurring before 17 years of age between January 1988 and December 1997 were matched with 1 control participant by sex, age, and geographical location. We recorded 140 study variables in a questionnaire that covered familial history of inflammatory bowel disease, events during the perinatal period, infant and child diet, vaccinations and childhood diseases, household amenities, and the family’s socioeconomic status.
Interventions	MMR vaccination
Outcomes	Crohn’s disease; ulcerative colitis
Funding Source	Government
Notes	Conclusions: whilst family history and appendicectomy are known risk factors, changes in risk based on domestic promiscuity, certain vaccinations, and dietary factors may provide new aetiological clues.
Risk of bias
Bias	Authors' judgement	Support for judgement
CCS ‐ case selection	Low risk	Adequate ‐ regional registry
CCS ‐ control selection	Unclear risk	Probable selection bias ‐ community ‐ random‐digit dialling
CCS ‐ comparability	Low risk	Case by age (2 years), sex, and living area (region)
CCS ‐ exposures	Unclear risk	Probable information bias ‐ exposition self‐reported
Summary Risk of Bias assessment	Unclear risk	We had concerns regarding at least 1 domain such that some doubt is raised about the results.