Understanding the Multidimensional Nature of Illness Severity as Measured by Patient-Reported Outcome Measures in Irritable Bowel Syndrome

Abstract

The concept of severity in irritable bowel syndrome (IBS) is clinically recognized and operative in making management decisions yet is poorly understood. Thus, the Rome Foundation Working Team Committee recently developed a consensus on this concept and made recommendations for its use in research and clinical care.1Drossman D.A. Chang L. Bellamy N. et al.Severity in irritable bowel syndrome: a Rome Foundation working team report.Am J Gastroenterol. 2011 Jul 12; (Epub ahead of print)Google Scholar The working team based the need and importance of a clearer understanding of IBS severity on several factors: (1) severity in IBS is determined by symptom reports and behaviors rather than by objective data; (2) categories of severity can influence diagnostic decisions and treatment planning; (3) there is no formalized way of categorizing IBS patients into clinically meaningful subgroups of severity; (4) severity needs to be understood within a psychosocial context; and (5) a better understanding of severity in IBS will help third party payers and regulatory agencies to establish treatment guidelines.1Drossman D.A. Chang L. Bellamy N. et al.Severity in irritable bowel syndrome: a Rome Foundation working team report.Am J Gastroenterol. 2011 Jul 12; (Epub ahead of print)Google Scholar There is currently no valid patient-reported outcome (PRO) instrument measuring IBS severity that was developed following the Food and Drug Administration (FDA) PRO guidance.2US Food and Drug AdministrationGuidance for industry Patient-reported outcome measures: use in medical product development to support labeling claims.http://www.fda.gov/downloads/Drugs/GuidanceComplianceRegulatoryInformation/Guidances/UCM193282Date: 2009Google Scholar However, there are several severity measures that have been used in IBS studies. Lackner and colleagues3Lackner J, Jaccard J, Baum C, et al. Patient-reported outcomes for irritable bowel syndrome are associated with patients' severity ratings of gastrointestinal symptoms and psychological factors. Clin Gastroenterol Hepatol;9:957–964.Google Scholar explored the psychometric properties of 2 of these scales and the potential contributions of psychological factors.Two different PRO rating scales that have measured IBS severity are the Irritable Bowel Syndrome Severity Scoring System (IBS-SSS)4Francis C.Y. Morris J. Whorwell P.J. The irritable bowel severity scoring system: a simple method of monitoring irritable bowel syndrome and its progress.Aliment Pharmacol Ther. 1997; 11: 395-402Crossref PubMed Scopus (990) Google Scholar and the 21-point numeric rating scale (NRS).5Spiegel B. Strickland A. Naliboff B.D. et al.Predictors of patient-assessed illness severity in irritable bowel syndrome.Am J Gastroenterol. 2008; 103: 2536-2543Crossref PubMed Scopus (95) Google Scholar The IBS-SSS primarily evaluates the intensity of IBS symptoms, abdominal pain, distension, stool frequency and consistency, and interference with life in general over a 10-day period.4Francis C.Y. Morris J. Whorwell P.J. The irritable bowel severity scoring system: a simple method of monitoring irritable bowel syndrome and its progress.Aliment Pharmacol Ther. 1997; 11: 395-402Crossref PubMed Scopus (990) Google Scholar The other severity measure is a patient-assessed “overall severity of IBS symptoms,” over the past week as measured on a 21-point NRS (0–20, 20 = the most intense imaginable symptoms).6Spiegel B.M. Harris L.A. Lucak S.L. et al.Measuring IBS patient reported outcomes with a single item numeric rating scale: results from the PROOF cohort.Gastroenterology. 2008; 134: A-467Abstract Full Text PDF Google Scholar The latter scale was developed at University of California, Los Angeles (UCLA) along with a similar 21-point NRS measuring severity of “belly” pain. These scales were based on the single item 11-point NRS (0–10) supported by the Initiative on Methods, Measurement, and Pain Assessment in Clinical Trials (IMMPACT) for assessment of pain.7Dworkin R.H. Turk D.C. Farrar J.T. et al.Core outcome measures for chronic pain clinical trials: IMMPACT recommendations.Pain. 2005; 113: 9-19Abstract Full Text Full Text PDF PubMed Scopus (2498) Google Scholar In the study by Lackner et al,3Lackner J, Jaccard J, Baum C, et al. Patient-reported outcomes for irritable bowel syndrome are associated with patients' severity ratings of gastrointestinal symptoms and psychological factors. Clin Gastroenterol Hepatol;9:957–964.Google Scholar the psychometric properties of these 2 severity measures were evaluated in 98 Rome III-positive IBS patients (88% female, mean age 46.7 years) at an academic center. The correlation between the 2 IBS severity scales was 0.59. We previously tested the psychometric properties of the UCLA IBS severity NRS in 170 Rome III-positive IBS patients (79% female, mean age 43 years) who were recruited as part of a natural history cohort from academic and community gastroenterology practices across the US.5Spiegel B. Strickland A. Naliboff B.D. et al.Predictors of patient-assessed illness severity in irritable bowel syndrome.Am J Gastroenterol. 2008; 103: 2536-2543Crossref PubMed Scopus (95) Google Scholar, 6Spiegel B.M. Harris L.A. Lucak S.L. et al.Measuring IBS patient reported outcomes with a single item numeric rating scale: results from the PROOF cohort.Gastroenterology. 2008; 134: A-467Abstract Full Text PDF Google Scholar We similarly found a significant correlation between the 21-point NRS and IBS-SSS of 0.63. Furthermore, the correlation coefficient of the overall IBS severity NRS and UCLA pain severity NRS was 0.46 in both our previous study6Spiegel B.M. Harris L.A. Lucak S.L. et al.Measuring IBS patient reported outcomes with a single item numeric rating scale: results from the PROOF cohort.Gastroenterology. 2008; 134: A-467Abstract Full Text PDF Google Scholar and Lackner's study.3Lackner J, Jaccard J, Baum C, et al. Patient-reported outcomes for irritable bowel syndrome are associated with patients' severity ratings of gastrointestinal symptoms and psychological factors. Clin Gastroenterol Hepatol;9:957–964.Google Scholar Thus, the current study validates the degree of convergence between the UCLA IBS severity scale and the IBS-SSS and UCLA pain severity scale, which is impressive given the different patient populations. Lackner et al3Lackner J, Jaccard J, Baum C, et al. Patient-reported outcomes for irritable bowel syndrome are associated with patients' severity ratings of gastrointestinal symptoms and psychological factors. Clin Gastroenterol Hepatol;9:957–964.Google Scholar argued that severity scores are arbitrary unless the clinical meaningfulness of an observed change is known. This is an important point. Spiegel et al previously demonstrated the minimal clinically important difference (MCID) for both the UCLA IBS severity scale5Spiegel B. Strickland A. Naliboff B.D. et al.Predictors of patient-assessed illness severity in irritable bowel syndrome.Am J Gastroenterol. 2008; 103: 2536-2543Crossref PubMed Scopus (95) Google Scholar and IBS-SSS8Spiegel B. Bolus R. Harris L.A. et al.Measuring irritable bowel syndrome patient-reported outcomes with an abdominal pain numeric rating scale.Aliment Pharmacol Ther. 2009; 30: 1159-1170Crossref PubMed Scopus (78) Google Scholar based on a longitudinal natural history cohort of IBS patients with a repeat assessment at 3 months. The MCIDs for the UCLA IBS severity scale and IBS-SSS were 4 points6Spiegel B.M. Harris L.A. Lucak S.L. et al.Measuring IBS patient reported outcomes with a single item numeric rating scale: results from the PROOF cohort.Gastroenterology. 2008; 134: A-467Abstract Full Text PDF Google Scholar and 95 points,8Spiegel B. Bolus R. Harris L.A. et al.Measuring irritable bowel syndrome patient-reported outcomes with an abdominal pain numeric rating scale.Aliment Pharmacol Ther. 2009; 30: 1159-1170Crossref PubMed Scopus (78) Google Scholar respectively. Confirmation of these MCID values with treatment intervention studies is needed.Lackner et al3Lackner J, Jaccard J, Baum C, et al. Patient-reported outcomes for irritable bowel syndrome are associated with patients' severity ratings of gastrointestinal symptoms and psychological factors. Clin Gastroenterol Hepatol;9:957–964.Google Scholar also evaluated the associations of the 2 severity scales with pain severity, pain catastrophisizing, “bloating/distension,” “altered defecation,” anxiety sensitivity, and somatization. All of the variables were placed on a common metric by subtracting the lowest possible score from the observed score and then dividing this by the highest possible score. The usual calculation for standardizing a variable to a 0–10 metric would be to subtract the lowest possible score from the observed score and then divide by the highest score minus the lowest score. The calculation used in the study is acceptable for scales where the lowest possible score is “0.” This is the case for all of the scales except the Gastrointestinal Symptoms Rating Scale for IBS (GSRS-IBS),9Svedlund J. Sjödin I. Dotevall G. GSRS--a clinical rating scale for gastrointestinal symptoms in patients with irritable bowel syndrome and peptic ulcer disease.Dig Dis Sci. 1988; 33: 129-134Crossref PubMed Scopus (939) Google Scholar which was used to measure the bloating and defecatory symptoms. Each item is measured on a 7-point scale (1 = no discomfort, 7 = very severe discomfort). Therefore, the adjusted scores were likely lower in the study because the lowest possible score of 1 was not accounted for in the denominator. This could potentially affect the correlations of the gastrointestinal (GI) symptoms with the psychological and severity measures depending on which type of correlation analysis was used. Nonetheless, pain severity correlated most strongly with the 2 severity scales. This is supported by previous data,5Spiegel B. Strickland A. Naliboff B.D. et al.Predictors of patient-assessed illness severity in irritable bowel syndrome.Am J Gastroenterol. 2008; 103: 2536-2543Crossref PubMed Scopus (95) Google Scholar which also showed that bloating (21-point NRS) and defecatory symptoms (urgency and straining) were significantly associated with the UCLA overall IBS severity scale.5Spiegel B. Strickland A. Naliboff B.D. et al.Predictors of patient-assessed illness severity in irritable bowel syndrome.Am J Gastroenterol. 2008; 103: 2536-2543Crossref PubMed Scopus (95) Google Scholar In Lackner's study,3Lackner J, Jaccard J, Baum C, et al. Patient-reported outcomes for irritable bowel syndrome are associated with patients' severity ratings of gastrointestinal symptoms and psychological factors. Clin Gastroenterol Hepatol;9:957–964.Google Scholar bloating and overall severity were not significantly correlated but this could be due to the different types of survey scales used to measure bloating. With regard to the IBS-SSS, it is not surprising that pain and bloating/distension significantly correlated with this severity scale but defecatory symptoms did not. Two of the 5 IBS-SSS items measure abdominal pain and 1 measures distension. The only bowel habit item asks, “How satisfied are you with your bowel habit?” This is a general question and thus, the response may vary by predominant bowel habit or defecatory symptom and may not be sensitive enough to detect changes in individual symptoms. The defecatory symptom factor was an average of ease of stool passage, stool consistency, urgent need for defecation, and feeling of incomplete evacuation.While the current study shows that GI symptoms explain some of the variance in overall IBS severity scores, there also is a large proportion of variance that is not attributable to them but may be explained by psychological factors. Interestingly, this study found that pain catastrophisizing, somatization, and anxiety sensitivity had a direct association with GI symptoms but not with overall IBS severity. Thus, the effect of psychological factors on severity was mediated indirectly through their impact on GI symptoms. Previous focus groups and surveys support the impact of psychological distress on IBS severity.5Spiegel B. Strickland A. Naliboff B.D. et al.Predictors of patient-assessed illness severity in irritable bowel syndrome.Am J Gastroenterol. 2008; 103: 2536-2543Crossref PubMed Scopus (95) Google Scholar, 10Drossman D.A. Chang L. Schneck S. et al.A focus group assessment of patient perspectives on irritable bowel syndrome and illness severity.Dig Dis Sci. 2009; 54: 1532-1541Crossref PubMed Scopus (87) Google Scholar, 11Drossman D.A. Morris C.B. Schneck S. et al.International survey of patients with IBS: symptom features and their severity, health status, treatments, and risk taking to achieve clinical benefit.J Clin Gastroenterol. 2009; 43: 541-550Crossref PubMed Scopus (175) Google Scholar Lackner suggests “applying statistical methods for covarying out the contaminating influence of somatization and other psychological factors.”3Lackner J, Jaccard J, Baum C, et al. Patient-reported outcomes for irritable bowel syndrome are associated with patients' severity ratings of gastrointestinal symptoms and psychological factors. Clin Gastroenterol Hepatol;9:957–964.Google Scholar While it is important to eliminate error from a measurement, the removal of real variance is a separate issue. For example, removal of stool consistency data in the presence of laxative use in an attempt to remove error when measuring diarrhea in IBS is valid. However, controlling for pain intensity when measuring stool consistency would likely lower the degree of diarrhea because pain is closely linked with diarrhea in IBS. But this does not mean that diarrhea is any less severe than that experienced in painless diarrhea. Severity can be a reflection of a symptom experience or a behavior. Psychological factors and severity of a chronic illness such as IBS are likely intertwined. As self-reported severity increases, there is a concurrent increase in both physical and psychosocial distress, comorbid somatic symptoms and maladaptive coping behaviors.1Drossman D.A. Chang L. Bellamy N. et al.Severity in irritable bowel syndrome: a Rome Foundation working team report.Am J Gastroenterol. 2011 Jul 12; (Epub ahead of print)Google Scholar Declaring psychological factors separate from severity in IBS would require examining the pathophysiologic mechanisms of both and determining if they are separate entities. “Purifying” PROs by adjusting for other potentially influential factors can be considered but it is essential that we understand what we are actually measuring and what this adjusted measure means. The concept of severity in irritable bowel syndrome (IBS) is clinically recognized and operative in making management decisions yet is poorly understood. Thus, the Rome Foundation Working Team Committee recently developed a consensus on this concept and made recommendations for its use in research and clinical care.1Drossman D.A. Chang L. Bellamy N. et al.Severity in irritable bowel syndrome: a Rome Foundation working team report.Am J Gastroenterol. 2011 Jul 12; (Epub ahead of print)Google Scholar The working team based the need and importance of a clearer understanding of IBS severity on several factors: (1) severity in IBS is determined by symptom reports and behaviors rather than by objective data; (2) categories of severity can influence diagnostic decisions and treatment planning; (3) there is no formalized way of categorizing IBS patients into clinically meaningful subgroups of severity; (4) severity needs to be understood within a psychosocial context; and (5) a better understanding of severity in IBS will help third party payers and regulatory agencies to establish treatment guidelines.1Drossman D.A. Chang L. Bellamy N. et al.Severity in irritable bowel syndrome: a Rome Foundation working team report.Am J Gastroenterol. 2011 Jul 12; (Epub ahead of print)Google Scholar There is currently no valid patient-reported outcome (PRO) instrument measuring IBS severity that was developed following the Food and Drug Administration (FDA) PRO guidance.2US Food and Drug AdministrationGuidance for industry Patient-reported outcome measures: use in medical product development to support labeling claims.http://www.fda.gov/downloads/Drugs/GuidanceComplianceRegulatoryInformation/Guidances/UCM193282Date: 2009Google Scholar However, there are several severity measures that have been used in IBS studies. Lackner and colleagues3Lackner J, Jaccard J, Baum C, et al. Patient-reported outcomes for irritable bowel syndrome are associated with patients' severity ratings of gastrointestinal symptoms and psychological factors. Clin Gastroenterol Hepatol;9:957–964.Google Scholar explored the psychometric properties of 2 of these scales and the potential contributions of psychological factors. Two different PRO rating scales that have measured IBS severity are the Irritable Bowel Syndrome Severity Scoring System (IBS-SSS)4Francis C.Y. Morris J. Whorwell P.J. The irritable bowel severity scoring system: a simple method of monitoring irritable bowel syndrome and its progress.Aliment Pharmacol Ther. 1997; 11: 395-402Crossref PubMed Scopus (990) Google Scholar and the 21-point numeric rating scale (NRS).5Spiegel B. Strickland A. Naliboff B.D. et al.Predictors of patient-assessed illness severity in irritable bowel syndrome.Am J Gastroenterol. 2008; 103: 2536-2543Crossref PubMed Scopus (95) Google Scholar The IBS-SSS primarily evaluates the intensity of IBS symptoms, abdominal pain, distension, stool frequency and consistency, and interference with life in general over a 10-day period.4Francis C.Y. Morris J. Whorwell P.J. The irritable bowel severity scoring system: a simple method of monitoring irritable bowel syndrome and its progress.Aliment Pharmacol Ther. 1997; 11: 395-402Crossref PubMed Scopus (990) Google Scholar The other severity measure is a patient-assessed “overall severity of IBS symptoms,” over the past week as measured on a 21-point NRS (0–20, 20 = the most intense imaginable symptoms).6Spiegel B.M. Harris L.A. Lucak S.L. et al.Measuring IBS patient reported outcomes with a single item numeric rating scale: results from the PROOF cohort.Gastroenterology. 2008; 134: A-467Abstract Full Text PDF Google Scholar The latter scale was developed at University of California, Los Angeles (UCLA) along with a similar 21-point NRS measuring severity of “belly” pain. These scales were based on the single item 11-point NRS (0–10) supported by the Initiative on Methods, Measurement, and Pain Assessment in Clinical Trials (IMMPACT) for assessment of pain.7Dworkin R.H. Turk D.C. Farrar J.T. et al.Core outcome measures for chronic pain clinical trials: IMMPACT recommendations.Pain. 2005; 113: 9-19Abstract Full Text Full Text PDF PubMed Scopus (2498) Google Scholar In the study by Lackner et al,3Lackner J, Jaccard J, Baum C, et al. Patient-reported outcomes for irritable bowel syndrome are associated with patients' severity ratings of gastrointestinal symptoms and psychological factors. Clin Gastroenterol Hepatol;9:957–964.Google Scholar the psychometric properties of these 2 severity measures were evaluated in 98 Rome III-positive IBS patients (88% female, mean age 46.7 years) at an academic center. The correlation between the 2 IBS severity scales was 0.59. We previously tested the psychometric properties of the UCLA IBS severity NRS in 170 Rome III-positive IBS patients (79% female, mean age 43 years) who were recruited as part of a natural history cohort from academic and community gastroenterology practices across the US.5Spiegel B. Strickland A. Naliboff B.D. et al.Predictors of patient-assessed illness severity in irritable bowel syndrome.Am J Gastroenterol. 2008; 103: 2536-2543Crossref PubMed Scopus (95) Google Scholar, 6Spiegel B.M. Harris L.A. Lucak S.L. et al.Measuring IBS patient reported outcomes with a single item numeric rating scale: results from the PROOF cohort.Gastroenterology. 2008; 134: A-467Abstract Full Text PDF Google Scholar We similarly found a significant correlation between the 21-point NRS and IBS-SSS of 0.63. Furthermore, the correlation coefficient of the overall IBS severity NRS and UCLA pain severity NRS was 0.46 in both our previous study6Spiegel B.M. Harris L.A. Lucak S.L. et al.Measuring IBS patient reported outcomes with a single item numeric rating scale: results from the PROOF cohort.Gastroenterology. 2008; 134: A-467Abstract Full Text PDF Google Scholar and Lackner's study.3Lackner J, Jaccard J, Baum C, et al. Patient-reported outcomes for irritable bowel syndrome are associated with patients' severity ratings of gastrointestinal symptoms and psychological factors. Clin Gastroenterol Hepatol;9:957–964.Google Scholar Thus, the current study validates the degree of convergence between the UCLA IBS severity scale and the IBS-SSS and UCLA pain severity scale, which is impressive given the different patient populations. Lackner et al3Lackner J, Jaccard J, Baum C, et al. Patient-reported outcomes for irritable bowel syndrome are associated with patients' severity ratings of gastrointestinal symptoms and psychological factors. Clin Gastroenterol Hepatol;9:957–964.Google Scholar argued that severity scores are arbitrary unless the clinical meaningfulness of an observed change is known. This is an important point. Spiegel et al previously demonstrated the minimal clinically important difference (MCID) for both the UCLA IBS severity scale5Spiegel B. Strickland A. Naliboff B.D. et al.Predictors of patient-assessed illness severity in irritable bowel syndrome.Am J Gastroenterol. 2008; 103: 2536-2543Crossref PubMed Scopus (95) Google Scholar and IBS-SSS8Spiegel B. Bolus R. Harris L.A. et al.Measuring irritable bowel syndrome patient-reported outcomes with an abdominal pain numeric rating scale.Aliment Pharmacol Ther. 2009; 30: 1159-1170Crossref PubMed Scopus (78) Google Scholar based on a longitudinal natural history cohort of IBS patients with a repeat assessment at 3 months. The MCIDs for the UCLA IBS severity scale and IBS-SSS were 4 points6Spiegel B.M. Harris L.A. Lucak S.L. et al.Measuring IBS patient reported outcomes with a single item numeric rating scale: results from the PROOF cohort.Gastroenterology. 2008; 134: A-467Abstract Full Text PDF Google Scholar and 95 points,8Spiegel B. Bolus R. Harris L.A. et al.Measuring irritable bowel syndrome patient-reported outcomes with an abdominal pain numeric rating scale.Aliment Pharmacol Ther. 2009; 30: 1159-1170Crossref PubMed Scopus (78) Google Scholar respectively. Confirmation of these MCID values with treatment intervention studies is needed. Lackner et al3Lackner J, Jaccard J, Baum C, et al. Patient-reported outcomes for irritable bowel syndrome are associated with patients' severity ratings of gastrointestinal symptoms and psychological factors. Clin Gastroenterol Hepatol;9:957–964.Google Scholar also evaluated the associations of the 2 severity scales with pain severity, pain catastrophisizing, “bloating/distension,” “altered defecation,” anxiety sensitivity, and somatization. All of the variables were placed on a common metric by subtracting the lowest possible score from the observed score and then dividing this by the highest possible score. The usual calculation for standardizing a variable to a 0–10 metric would be to subtract the lowest possible score from the observed score and then divide by the highest score minus the lowest score. The calculation used in the study is acceptable for scales where the lowest possible score is “0.” This is the case for all of the scales except the Gastrointestinal Symptoms Rating Scale for IBS (GSRS-IBS),9Svedlund J. Sjödin I. Dotevall G. GSRS--a clinical rating scale for gastrointestinal symptoms in patients with irritable bowel syndrome and peptic ulcer disease.Dig Dis Sci. 1988; 33: 129-134Crossref PubMed Scopus (939) Google Scholar which was used to measure the bloating and defecatory symptoms. Each item is measured on a 7-point scale (1 = no discomfort, 7 = very severe discomfort). Therefore, the adjusted scores were likely lower in the study because the lowest possible score of 1 was not accounted for in the denominator. This could potentially affect the correlations of the gastrointestinal (GI) symptoms with the psychological and severity measures depending on which type of correlation analysis was used. Nonetheless, pain severity correlated most strongly with the 2 severity scales. This is supported by previous data,5Spiegel B. Strickland A. Naliboff B.D. et al.Predictors of patient-assessed illness severity in irritable bowel syndrome.Am J Gastroenterol. 2008; 103: 2536-2543Crossref PubMed Scopus (95) Google Scholar which also showed that bloating (21-point NRS) and defecatory symptoms (urgency and straining) were significantly associated with the UCLA overall IBS severity scale.5Spiegel B. Strickland A. Naliboff B.D. et al.Predictors of patient-assessed illness severity in irritable bowel syndrome.Am J Gastroenterol. 2008; 103: 2536-2543Crossref PubMed Scopus (95) Google Scholar In Lackner's study,3Lackner J, Jaccard J, Baum C, et al. Patient-reported outcomes for irritable bowel syndrome are associated with patients' severity ratings of gastrointestinal symptoms and psychological factors. Clin Gastroenterol Hepatol;9:957–964.Google Scholar bloating and overall severity were not significantly correlated but this could be due to the different types of survey scales used to measure bloating. With regard to the IBS-SSS, it is not surprising that pain and bloating/distension significantly correlated with this severity scale but defecatory symptoms did not. Two of the 5 IBS-SSS items measure abdominal pain and 1 measures distension. The only bowel habit item asks, “How satisfied are you with your bowel habit?” This is a general question and thus, the response may vary by predominant bowel habit or defecatory symptom and may not be sensitive enough to detect changes in individual symptoms. The defecatory symptom factor was an average of ease of stool passage, stool consistency, urgent need for defecation, and feeling of incomplete evacuation. While the current study shows that GI symptoms explain some of the variance in overall IBS severity scores, there also is a large proportion of variance that is not attributable to them but may be explained by psychological factors. Interestingly, this study found that pain catastrophisizing, somatization, and anxiety sensitivity had a direct association with GI symptoms but not with overall IBS severity. Thus, the effect of psychological factors on severity was mediated indirectly through their impact on GI symptoms. Previous focus groups and surveys support the impact of psychological distress on IBS severity.5Spiegel B. Strickland A. Naliboff B.D. et al.Predictors of patient-assessed illness severity in irritable bowel syndrome.Am J Gastroenterol. 2008; 103: 2536-2543Crossref PubMed Scopus (95) Google Scholar, 10Drossman D.A. Chang L. Schneck S. et al.A focus group assessment of patient perspectives on irritable bowel syndrome and illness severity.Dig Dis Sci. 2009; 54: 1532-1541Crossref PubMed Scopus (87) Google Scholar, 11Drossman D.A. Morris C.B. Schneck S. et al.International survey of patients with IBS: symptom features and their severity, health status, treatments, and risk taking to achieve clinical benefit.J Clin Gastroenterol. 2009; 43: 541-550Crossref PubMed Scopus (175) Google Scholar Lackner suggests “applying statistical methods for covarying out the contaminating influence of somatization and other psychological factors.”3Lackner J, Jaccard J, Baum C, et al. Patient-reported outcomes for irritable bowel syndrome are associated with patients' severity ratings of gastrointestinal symptoms and psychological factors. Clin Gastroenterol Hepatol;9:957–964.Google Scholar While it is important to eliminate error from a measurement, the removal of real variance is a separate issue. For example, removal of stool consistency data in the presence of laxative use in an attempt to remove error when measuring diarrhea in IBS is valid. However, controlling for pain intensity when measuring stool consistency would likely lower the degree of diarrhea because pain is closely linked with diarrhea in IBS. But this does not mean that diarrhea is any less severe than that experienced in painless diarrhea. Severity can be a reflection of a symptom experience or a behavior. Psychological factors and severity of a chronic illness such as IBS are likely intertwined. As self-reported severity increases, there is a concurrent increase in both physical and psychosocial distress, comorbid somatic symptoms and maladaptive coping behaviors.1Drossman D.A. Chang L. Bellamy N. et al.Severity in irritable bowel syndrome: a Rome Foundation working team report.Am J Gastroenterol. 2011 Jul 12; (Epub ahead of print)Google Scholar Declaring psychological factors separate from severity in IBS would require examining the pathophysiologic mechanisms of both and determining if they are separate entities. “Purifying” PROs by adjusting for other potentially influential factors can be considered but it is essential that we understand what we are actually measuring and what this adjusted measure means. Patient-Reported Outcomes for Irritable Bowel Syndrome Are Associated With Patients' Severity Ratings of Gastrointestinal Symptoms and Psychological FactorsClinical Gastroenterology and HepatologyVol. 9Issue 11PreviewPatient-reported outcomes (PROs) are used to gauge the benefit of treatments for functional gastrointestinal disorders, including irritable bowel syndrome (IBS). Commonly used end points derived from scales of symptom severity differ in their structure, format, and the extent to which they are based on established psychometric fundamentals. We evaluated the overlap between 2 measures of IBS symptom severity, documented their association with different symptoms (pain, bloating, altered defecation), and identified psychological factors that might bias PRO ratings, by affecting how patients interpret IBS symptom severity. Full-Text PDF