title: Randomized patients in IBS research had different disease characteristics compared to eligible and recruited patients.
abstract: OBJECTIVE
  The recruitment process may generate a selected patient sample, which may threaten the generalizability of trial results. This risk is particularly high in case disease and patient characteristics demonstrate a wide variation, such as in irritable bowel syndrome (IBS). We compared IBS patients who were selected, approached, and randomized to participate in a clinical trial assessing the efficacy of dietary fiber therapy in IBS.
  
  
  METHODS
  Retrospective survey in primary care patients diagnosed with IBS by their general practitioner in the past 2 years selected and invited for participation in a trial. Characteristics were compared between randomized patients (n=193) nonrandomized eligible patients (n=371), and patients not eligible for participating in the trial (n=724).
  
  
  RESULTS
  Of the 2,100 IBS patients, 1,288 (61%) returned the questionnaire. Randomized patients had a higher intensity of IBS abdominal pain as compared to the other groups, a higher consultation rate and a longer IBS disease history. Noneligible patients had less active IBS symptoms.
  
  
  CONCLUSIONS
  Patients randomized do differ from those nonrandomized in IBS disease characteristics. These observations may have implications for the applicability of our research outcome.
authors.affiliation: Julius Center for Health Sciences and Primary Care, University Medical Center Utrecht, The Netherlands. c.j.bijkerk-2@umcutrecht.nl
authors.forename: C J
authors.initials: CJ
authors.lastname: Bijkerk
authors.forename: J W M
authors.initials: JW
authors.lastname: Muris
authors.forename: J A
authors.initials: JA
authors.lastname: Knottnerus
authors.forename: A W
authors.initials: AW
authors.lastname: Hoes
authors.forename: N J
authors.initials: NJ
authors.lastname: de Wit
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D004043:Dietary Fiber / Q000627:therapeutic use*; D006801:Humans; D043183:Irritable Bowel Syndrome / Q000175:diagnosis / Q000178:diet therapy*; D008875:Middle Aged; D010342:Patient Acceptance of Health Care / Q000706:statistics & numerical data; D018579:Patient Selection; D011320:Primary Health Care / Q000379:methods; D015983:Selection Bias; D012720:Severity of Illness Index; D055815:Young Adult