title: Evaluation of the Irritable Bowel Syndrome Quality of Life (IBS-QOL) questionnaire in diarrheal-predominant irritable bowel syndrome patients.
abstract: BACKGROUND
  Diarrhea-predominant irritable bowel syndrome (IBS-d) significantly diminishes the health-related quality of life (HRQOL) of patients. Psychological and social impacts are common with many IBS-d patients reporting comorbid depression, anxiety, decreased intimacy, and lost working days. The Irritable Bowel Syndrome Quality of Life (IBS-QOL) questionnaire is a 34-item instrument developed and validated for measurement of HRQOL in non-subtyped IBS patients. The current paper assesses this previously-validated instrument employing data collected from 754 patients who participated in a randomized clinical trial of a novel treatment, eluxadoline, for IBS-d.
  
  
  METHODS
  Psychometric methods common to HRQOL research were employed to evaluate the IBS-QOL. Many of the historical analyses of the IBS-QOL validations were used. Other techniques that extended the original methods were applied where more appropriate for the current dataset. In IBS-d patients, we analyzed the items and substructure of the IBS-QOL via item reduction, factor structure, internal consistency, reproducibility, construct validity, and ability to detect change.
  
  
  RESULTS
  This study supports the IBS-QOL as a psychometrically valid measure. Factor analyses suggested that IBS-specific QOL as measured by the IBS-QOL is a unidimensional construct. Construct validity was further buttressed by significant correlations between IBS-QOL total scores and related measures of IBS-d severity including the historically-relevant Irritable Bowel Syndrome Adequate Relief (IBS-AR) item and the FDA's Clinical Responder definition. The IBS-QOL also showed a significant ability to detect change as evidenced by analysis of treatment effects. A minority of the items, unrelated to the IBS-d, performed less well by the standards set by the original authors.
  
  
  CONCLUSIONS
  We established that the IBS-QOL total score is a psychometrically valid measure of HRQOL in IBS-d patients enrolled in this study. Our analyses suggest that the IBS-QOL items demonstrate very good construct validity and ability to detect changes due to treatment effects. Furthermore, our analyses suggest that the IBS-QOL items measure a univariate construct and we believe further modeling of the IBS-QOL from an item response theory (IRT) approach under both non-treatment and treatment conditions would greatly further our understanding as item-based methods could be used to develop a short form.
authors: Furiex Pharmaceuticals, Inc,, 3900 Paramount Parkway, Suite 150, Morrisville, NC 27560, USA. David.Andrae@furiex.com.
authors: David A
authors: DA
authors: Andrae
authors: Donald L
authors: DL
authors: Patrick
authors: Douglas A
authors: DA
authors: Drossman
authors: Paul S
authors: PS
authors: Covington
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D003967:Diarrhea / Q000523:psychology*; D004305:Dose-Response Relationship, Drug; D005163:Factor Analysis, Statistical; D005260:Female; D006801:Humans; D043183:Irritable Bowel Syndrome / Q000188:drug therapy / Q000503:physiopathology / Q000523:psychology*; D008297:Male; D008875:Middle Aged; D017060:Patient Satisfaction; D011594:Psychometrics; D011788:Quality of Life / Q000523:psychology*; D016032:Randomized Controlled Trials as Topic; D011795:Surveys and Questionnaires / Q000592:standards*; D014481:United States; D055815:Young Adult