Risk and PAR of (a) Crohn’s disease and (b) ulcerative colitis according to modifiable risk scores. Reference level for UC set to 0–2 given low number of scores 0–1. a Cox models stratified by age (months), time-period (2-year intervals), and cohort (NHS, NHSII, or HPFS), and adjusted for appendectomy (yes/no), and family history of IBD (yes/no). b PAR for binary comparison between high-MRS (2+ risk factors for CD or 3+ risk factors for UC) and low-MRS (reference), adjusted for age (<40, 40 ≤ age <60, ≥ 60 years), cohort (NHS, NHSII, HPFS), appendectomy (yes/no) and family history of IBD (yes/no). CD Crohn’s Disease. CI Confidence Interval. aHR Multivariable-adjusted Hazard Ratio. MRS Modifiable Risk Score. PAR Population Attributable Risk. UC Ulcerative Colitis.