Objective: The aim of this study was to estimate the prevalence of irritable bowel syndrome using different standard definitions (Rome and Manning criteria) and to determine the degree of agreement between these definitions.

Methods: A population-based, cross-sectional survey study was conducted by mailing a valid, reliable questionnaire to an age- and gender-stratified random sample of residents of Olmsted County, MN, aged 30-69 yr. The threshold for a positive diagnosis of irritable bowel was varied from two to four of the six Manning criteria and from two to three of the five defecation disorders in the Rome criteria. Unadjusted as well as age- and gender-adjusted prevalence rates were calculated for each of the five definitions of IBS. Percent agreement and kappa statistics were calculated to assess agreement between the definitions.

Results: Questionnaires were returned by 643 of 892 eligible subjects (72% response rate). The age- and gender-adjusted prevalence of IBS varied from 20.4% using a threshold of two symptoms in the Manning criteria to 8.5% using a threshold of three defecation disorders in the Rome criteria. The percent agreement for each comparison of Manning and Rome definitions was always >90%. The kappa values ranged from 0.55 to 0.78, with the best agreement occurring between a threshold of three symptoms of Manning and two defecation disorders in Rome.

Conclusions: The prevalence of IBS varied substantially depending on the specific definition of IBS used. The range of prevalence estimates in Olmsted County was similar to other published figures when IBS definition was accounted for. These findings are useful in interpreting epidemiological and clinical studies of IBS.