Methodology for high-quality studies on course and prognosis of inflammatory bowel disease

Inflammatory bowel diseases（IBDs） are characterized by a chronic course with an alternation of relapses and remissions.Questions about prognosis are important for the patient who wants to know how the disease will affect his/her life and also for clinicians to make management decisions.Correct selection of the patients is the basis for good methodological studies on the course of IBD.A great proportion of data on the course of IBD is derived from a limited number of cohort studies.Studies help to define the endpoints for clinical trials and to identify subsets of patients in whom the prognosis of the disease can be stratified according to clinical features.Specific scientific requirements for high-quality studies on prognosis are the following：use of inception cohort,description of referral patterns,completeness of follow-up,objective outcome criteria,blind outcome assessment,adjustment for extraneous prognostic factors and statistical issues.We analyzed each of these requirements in studies on IBDs.To date,prospective and populationbased cohort studies are the standard for an unbiased assessment of prognosis.A better knowledge of the course of disease of chronic disorders ideally requires：（1） data from population-based studies,to avoid selection bias from referral centers in which patients with a more severe disease are usually treated;（2） inclusion of patients seen at the onset of the disease excluding misdiagnosed cases;and（3） follow-up from the onset of the disease to the end without dropouts.