title: Healthy control subjects are poorly defined in case-control studies of irritable bowel syndrome.
abstract: BACKGROUND
  Case-control studies are vital for understanding the pathophysiology of gastrointestinal disease. While the definition of disease is clear, the definition of healthy control is not. This is particularly relevant for functional bowel diseases such as irritable bowel syndrome (IBS). In this study, a systematic review formed the basis for a prospective study evaluating the effectiveness of commonly used techniques for defining healthy controls in IBS.
  
  
  METHODS
  A systematic review of the literature was conducted to identify case-control studies involving functional gastrointestinal disorders. "Lack of Rome criteria", self-description as "healthy" and the bowel disease questionnaire (BDQ) were common methods for identifying healthy controls. These 3 methods were then applied to a cohort of 53 non-patient subjects to determine their validity compared to objective outcome measures (7-day stool diary).
  
  
  RESULTS
  "Lack of Rome criteria" and "healthy" self-description were the most common methods for identifying healthy control subjects, but many studies failed to describe the methods used. In the prospective study, more subjects were identified as non-healthy using the BDQ than using either lack of Rome criteria (P=0.01) or "healthy" self-description (P=0.026). Furthermore, stool diaries identified several subjects with abnormal stool form and/or frequency which were not identified using lack of Rome criteria or the "healthy" question. Comparisons revealed no agreement (κ) between the different methods for defining healthy controls.
  
  
  CONCLUSIONS
  The definitions of healthy controls in studies of functional bowel diseases such as IBS are inconsistent. Since functional symptoms are common, a strict definition of "normal" is needed in this area of research.
authors.affiliation: GI Motility Program, Cedars-Sinai Medical Center, Los Angeles (Shireen Ghorbani, Amir Nejad, Kathleen S. Chua, Meridythe M. Amichai, Mark Pimentel), California, USA.
authors.forename: Shireen
authors.initials: S
authors.lastname: Ghorbani
authors.affiliation: GI Motility Program, Cedars-Sinai Medical Center, Los Angeles (Shireen Ghorbani, Amir Nejad, Kathleen S. Chua, Meridythe M. Amichai, Mark Pimentel), California, USA.
authors.forename: Amir
authors.initials: A
authors.lastname: Nejad
authors.affiliation: Harbor UCLA Medical Center, Torrance (David Law), California, USA.
authors.forename: David
authors.initials: D
authors.lastname: Law
authors.affiliation: GI Motility Program, Cedars-Sinai Medical Center, Los Angeles (Shireen Ghorbani, Amir Nejad, Kathleen S. Chua, Meridythe M. Amichai, Mark Pimentel), California, USA.
authors.forename: Kathleen S
authors.initials: KS
authors.lastname: Chua
authors.affiliation: GI Motility Program, Cedars-Sinai Medical Center, Los Angeles (Shireen Ghorbani, Amir Nejad, Kathleen S. Chua, Meridythe M. Amichai, Mark Pimentel), California, USA.
authors.forename: Meridythe M
authors.initials: MM
authors.lastname: Amichai
authors.affiliation: GI Motility Program, Cedars-Sinai Medical Center, Los Angeles (Shireen Ghorbani, Amir Nejad, Kathleen S. Chua, Meridythe M. Amichai, Mark Pimentel), California, USA.
authors.forename: Mark
authors.initials: M
authors.lastname: Pimentel
keywords: Keywords Irritable bowel syndrome; functional GI disorders; healthy control