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Psychosomatic Medicine 68:312-320 (2006)
© 2006 American Psychosomatic Society

ORIGINAL ARTICLES

Measuring Health-Related Quality of Life in Patients With Irritable Bowel Syndrome: Can Less Be More?

Jeffrey M. Lackner, PsyD, Gregory D. Gudleski, PhD, Matthew M. Zack, MD, Leonard A. Katz, MD, Catherine Powell, BA, Susan Krasner, PhD, Elizabeth Holmes, MA and Kathryn Dorscheimer, BA

From the Division of Gastroenterology, Department of Medicine (J.M.L., G.D.G., L.A.K., C.P., E.H., K.D.) and the Department of Anesthesiology (S.K.), University at Buffalo School of Medicine and Biomedical Sciences, State University of New York, Buffalo, New York; and the Health Care and Aging Studies Branch, Division of Adult and Community Health (M.M.Z.), National Center for Chronic Disease Prevention and Health Promotion, Centers for Disease Control and Prevention, Atlanta, Georgia.

Address correspondence and reprint requests to Jeffrey M. Lackner, PsyD, Behavioral Medicine Clinic, Department of Medicine, UB School of Medicine, SUNY, ECMC, 462 Grider Street, Buffalo, NY 14215. E-mail: lackner{at}buffalo.edu


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 DISCUSSION
 NOTES
 REFERENCES
 
Objective: This study assessed the ability of a brief, well-validated generic health-related quality of life (HRQOL) measure to characterize the symptom burden of patients with irritable bowel syndrome (IBS) with reference to a large survey of U.S. community-living adults.

Methods: One hundred four Rome II diagnosed patients with IBS completed measures of pain, psychological dysfunction (neuroticism, somatization, distress, abuse), and HRQOL (SF-36, IBS-QOL, CDC HRQOL-4) during baseline assessment of a National Institutes of Health-funded clinical trial. The four-item CDC HRQOL-4 assesses global health and the number of days in the past 30 days resulting from poor physical health, poor mental health, and activity limitation.

Results: Patients with IBS averaged 15 of 30 days with poor physical or mental health. These average overall unhealthy days exceeded those of respondents with arthritis, diabetes, heart disease/stroke, cancer, and class III obesity (body mass index ≥40 kg/m2) from the U.S. survey. Fifteen percent of patients identified musculoskeletal disorders, not IBS symptoms, as the major cause of their activity limitation. Overall unhealthy days among patients with IBS varied directly with IBS symptom severity, abuse, pain, and psychological distress. Controlling for personality variables that influence perception and reporting HRQOL did not diminish the statistical significance of associations between the CDC HRQOL-4 and other study measures.

Conclusions: The CDC HRQOL-4 is a psychometrically sound, rapid, and efficient instrument whose HRQOL profile reflects the symptom burden of moderate-to-severe IBS, is sensitive to treatment effects associated with cognitive behavior therapy, and is not a proxy for personality variables identified as potential confounders of HRQOL. HRQOL is related to but not redundant with psychological distress.

Key Words: generic health status • quality of life • irritable bowel syndrome • anxiety • somatization

Abbreviations: GERD = gastroesophageal reflux disease; HRQOL = health-related quality of life; IBS = irritable bowel syndrome; BRFSS = Behavioral Risk Factor Surveillance System; CDC = Centers for Disease Control and Prevention.


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 DISCUSSION
 NOTES
 REFERENCES
 
Irritable bowel syndrome (IBS) is a prevalent, painful, often disabling gastrointestinal disorder whose symptoms cannot be ascribed to structural or biochemical abnormalities. Because IBS is a medically benign gastrointestinal disorder, no specific biomarker exists for gauging patient status. Interest is therefore growing with respect to nonpathological indices of patients' level of function and perceptions of their physical and mental health over time, the construct referred to as health-related quality of life (HRQOL) (1,2). One measure of the importance of HRQOL comes from research showing that patients with IBS describe their HRQOL as similar to or worse than that of patients with more serious or life-threatening illnesses such as gastroesophageal reflux disease (GERD), asthma, and end-stage renal disease (3–5). For these reasons, medical and regulatory (U.S. Food and Drug Administration) institutions recommend routine assessment of HRQOL of more severely affected patients (6).

Significant practical barriers prevent the widespread adoption of HRQOL assessment. These barriers include confusion about what defines quality of life; uncertainty about the best questions to ask patients for capturing it; the length, cost, and/or complexity (e.g., scoring procedures) of existing quality-of-life instruments; physician beliefs that clinical judgments are both more accurate in measuring outcome than data abstracted from questionnaires and less likely to "open a Pandora's box" of problems (psychological distress, relationship problems); and time limitations inherent in busy clinical settings (7). For these reasons, the assessment of HRQOL is largely confined to research settings.

That said, relatively small reductions in the demands imposed on clinical staff and patients may reduce these barriers, facilitate the implementation of HRQOL assessment in routine clinical practice, and enhance physicians' ability to manage more complex patients (8). One strategy involves decreasing the number of assessment items required to derive a HRQOL index. A useful screening measure should also 1) be based on a precise definition of HRQOL; 2) reflect the symptom burden of physical and mental problems and disability associated with IBS; 3) correlate with widely used quality-of-life measures (which, in the case of IBS, includes the SF-36 Health Survey, IBS-Quality of Life Inventory); 4) be simple to administer, calculate, and interpret; and 5) be capable of quickly generating clinically meaningful information that informs clinical decision-making and tracks the impact of interventions on patients' lives (i.e., sensitive to change).

One promising method is the CDC HRQOL measure (9). Developed by the Centers for Disease Control and Prevention, the CDC HRQOL was designed to address the need for a brief, reliable, and valid overall HRQOL measure that conforms to the fundamental concept of health ("a state of complete physical, mental and social well-being, not merely the absence of disease or infirmity") defined by the World Health Organization (10). The CDC HRQOL assumes that HRQOL is a fundamentally subjective construct whose core features (physical and mental health appraisal) are expressed through patients' judgments of their general health and the number of days within the past month when they felt physically unhealthy, mentally unhealthy, and limited their activities because of their health. These responses are elicited by four questions that comprise the core module of the CDC HRQOL (CDC HRQOL-4; Fig. 1). The CDC HRQOL also includes an optional set of 10 questions regarding activity limitations (five items) and recent symptoms of pain, depression, anxiety, sleeplessness, and vitality (five items) (9).


Figure 120
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  		Figure 1. Core items of the CDC HRQOL-4.

 

Notwithstanding its brevity, CDC HRQOL predicts health outcomes relevant to IBS (e.g., medical care utilization) (9,11). Its psychometric properties (reliability, validity) are comparable to those of the SF-36 Health Survey (9,12,13), which is generally accepted as a criterion or "gold standard" for HRQOL measurement and is the most widely used such instrument in IBS research (14,15). In criterion validity analyses in a large statewide sample representative of the U.S. population as a whole, CDC HRQOL items explain a majority (60–65%, respectively) of the variation in SF-36 physical and mental component summary scores (12). Like the SF-36 scales, CDC HRQOL items discriminate between well groups and groups with chronic physical and or mental health problems (12). For these reasons, the core CDC HRQOL module (CDC HRQOL-4) is regarded as "quite satisfactory" in comparison to 22 of the most widely used HRQOL instruments (16).

Because of its brevity and strong psychometric properties, the CDC HRQOL-4 is used routinely in the U.S. Behavioral Risk Factor Surveillance System (BRFSS), a large telephone survey in all 50 states and the District of Columbia continually collecting information on major health risk behaviors among noninstitutionalized adults. Although the CDC HRQOL-4 was not designed as a scale based on multiple indicators, but as a surveillance instrument to track distinct domains of (perceived) health-related quality of life, it performs well in clinical settings with patients with painful medical disorders highly comorbid with IBS (17,18). In a direct comparison of several rheumatic condition-specific health status and psychological measures, the CDC HRQOL validly distinguished groups of patients with fibromyalgia, osteoarthritis, and rheumatoid arthritis (17).

The clinical use of the CDC HRQOL-4 has not been extended to the problem of IBS. Our major goal was to assess the merits of the CDC HRQOL-4 among a large sample of more severely affected patients with IBS with respect to two validated instruments of HRQOL (SF-36, IBS QOL) used in IBS research. We reasoned a priori that support for the CDC HRQOL-4 would require at least moderately strong (r = 0.30–.50 [19]) zero-order correlations between number of unhealthy days and summary scales of the IBS QOL and SF-36. Although the quality-of-life literature generally regards moderately strong associations as "substantial" evidence supporting the performance of a quality-of-life instrument (20), a more rigorous test requires evidence that their responses are not simply a proxy for personality variables that influence the perception and reporting of quality of life (21). Particularly strong confounders of reported HRQOL are neuroticism (the personality trait of being "high strung, nervous or emotional" [22]) and somatization (21). Because both somatizing and neurotic individuals selectively favor the processing of threat-related information (23–25), it is unclear whether patients' judgments of well-being made as part of HRQOL assessment reflect their underlying HRQOL or only perceptual abnormalities specific to comorbid psychological dysfunction (e.g., attentional biases toward threat-related information, distorted judgments of risk, selective memory processing).

The question of whether personality variables confound patient ratings of HRQOL has largely eluded IBS researchers who have linked IBS to impaired HRQOL (1,14,26). The only published study (27) that addressed this question found that levels of somatization accounted for the relationship between IBS and diminished HRQOL (as measured by the SF-36) in a community (nontertiary care) sample of individuals with heterogeneous functional gastrointestinal complaints. The interpretability of these data are compromised by study imperfections, including inclusion of subjects whose diagnosis of IBS was based on subjective responses to a mail survey (not physician diagnosis), reliance on the less specific Manning diagnostic criteria but not the more restrictive Rome II diagnostic criteria, inclusion criteria that imposed no minimum frequency of symptom duration, and exclusion of subjects with extraintestinal symptoms. The current study was designed first to address these limitations with a large sample of patients whose IBS symptoms were of moderate to severe intensity and met Rome II criteria established through physician diagnosis. Second, we sought to test whether the CDC HRQOL-4 reflects the disease burden of IBS with reference to the health characteristics of a large sample of community-based subjects. Third, we tested the responsivity of the CDC HRQOL-4 to therapeutic change in a subset of IBS patients 2 weeks after undergoing an empirically validated, 10-week regimen of cognitive behavior therapy (28).


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
DISCUSSION
 NOTES
 REFERENCES
 
Subjects
Subjects included 104 consecutive patients with IBS recruited primarily through referral of local physicians as well as local media coverage and community advertising. To qualify, subjects must have met Rome II IBS diagnostic criteria (29) without organic gastrointestinal disease by the board-certified study gastroenterologist. Because this study was conducted as part of a clinical trial for more severely affected patients with IBS, they must also have experienced IBS symptoms of at least moderate intensity (i.e., symptom occurring at least twice weekly for 6 months and imposing some life restriction). After conducting a physical examination of patients to confirm Rome II diagnosis during pretreatment assessment, the study gastroenterologist (L.K.) rated their overall IBS symptom severity using a four-point rating scale (30) in which 1 = mild and 4 = very severe. The average severity score for the IBS group was 3.2, indicating a severely affected sample.

General population information from the CDC HRQOL-4 to compare with that from the study subjects comes mainly from two sources, the "core" BRFSS including 576,367 respondents in 50 states and the District of Columbia from 1993 through 1997 and an "optional" BRFSS module containing 10 additional HRQOL questions including 42,632 respondents in 13 selected states from 1995 through 1997 (CDC, unpublished data, 2000). Supplemental information on arthritis, heart disease, and stroke comes from the BRFSS during other years in some states ([31] K. J. Greenland, personal communication, 2005). The demographic composition of the BRFSS participants was primarily female (52%), white (87%), married (60.7%), high school-educated (average number of grades completed = 12.5), with a mean age of 44.3 years.

Procedure
This study was conceived, not as a study of convenience, but as a separate study conducted within a clinical trial of two psychological treatments that was conducted between 2000 and 2004. The Institutional Review Board of the University at Buffalo School of Medicine approved its experimental procedures, and all participants provided their informed consent. After a brief telephone interview to determine whether subjects were likely to meet basic inclusion criteria (e.g., moderate symptom severity, absence of comorbid gastrointestinal disease), subjects were scheduled for a medical examination to confirm IBS diagnosis and psychological testing, which for the purposes of this study, included the CDC HRQOL, SF-36 Health Survey, IBS Quality of Life Inventory, the Trait Anxiety Inventory, the Brief Symptom Inventory, the McGill Pain Questionnaire, and a self-report abuse history questionnaire. Two weeks after completing treatment, a subset of 54 subjects completed the CDC HRQOL and a global rating scale of improvement.

Measures
Brief Symptom Inventory
Psychological distress was assessed using the 52-item, Brief Symptom Inventory (32). Respondents indicate on a five-point scale (0 = not at all, 5 = extremely) their level of distress for nine types of problems (e.g., anxiety, somatization, depression). The average intensity of all items yields a composite index of psychological distress (Global Severity Index [GSI]). The GSI and its derivative subscales (e.g., somatization) have been used extensively to measure psychological distress in patients with IBS (33,34). Their psychometric properties (internal consistency, test-retest reliability, validity) are well established (32,35).

Pain
Pain was measured using the short form of the McGill Pain Questionnaire (SF-MPQ [36]). The SF-MPQ consists of 15 words reflecting the most commonly used adjectives use to describe the sensory (11 words) and affective (four words) quality of pain experience. Patients rate the intensity of these descriptors on a four-point scale (0 = none, 1 = mild, 2 = moderate, and 3 = severe). Summing these responses yields the McGill-Total global index of pain intensity. Subjects also rated the current intensity of pain using an 11-point visual analog scale (VAS: 0 = no pain, 10 = worst pain possible) whose psychometric properties are well established (37).

Neuroticism
We adopted the practice (38,39) of using the Trait subscale of the State-Trait Anxiety Inventory (40) to measure neuroticism. Its 20 items require subjects to indicate how they generally feel by rating the frequency of their feelings of anxiety on a four-point scale ranging from 1 (almost never) to 4 (almost always). The Trait scale of the STAI has sound psychometric properties (e.g., internal consistency, stability, validity [40]).

Abuse
Abuse was measured using a standard self report screening instrument (41) that asks subjects whether during either childhood (<14 years) or adulthood if "anyone [has] ever: exposed the sex organs of their body to you? threatened to have sex with you? touched the sex organs of your body? made you touch the sex organs of their body?" or "tried forcefully or succeeded to have sex when you didn't want this?" Subjects are considered to have been sexually abused if they answer affirmatively to any questions about sexual abuse except for the item regarding exposure. The physical abuse question asks subjects to respond to the question of whether as a "child (or now that you are an adult) did an older person (does any other adult) hit kick or beat you" using a four-point scale (1 = never, 2 = seldom, 3 = occasionally, or 4 = often). Subjects who answer "often" to this question were considered to have a positive history of physical abuse.

Health-Related Quality of Life
HRQOL was measured using three established instruments (SF-36 Health Survey [SF-36], IBS Quality of Life [IBS-QOL], CDC HRQOL-4). The SF-36 Health Survey is a generic quality-of-life instrument whose 36 items measure eight domains of health: physical functioning, role limitations resulting from physical health, bodily pain, general health perceptions, vitality, social functioning, role limitations resulting from emotional problems, and mental health. It yields scale scores for each of these eight health domains and two summary measures of physical and mental health, the Physical Component Summary (PCS) and Mental Component Summary (MCS). The IBS-QOL (26,42) is a 34-item measure constructed specifically to assess the subjective well-being of patients with IBS. Each item is scored on a five-point scale (1 = not at all, 5 = a great deal) that represents one of eight dimensions (dysphoria, interference with activity, body image, health worry, food avoidance, social reaction, sexual dysfunction, and relationships). Items are scored to derive an overall total score of IBS related quality of life. To facilitate score interpretation, the summed total score is transformed to a zero to 100 scale ranging from zero (poor quality of life) to 100 (maximum quality of life). The psychometric properties of the SF-36 and IBS QOL are well established and detailed elsewhere (20,43).

The core BRFSS module of the CDC HRQOL-4 (9) includes four questions (Fig. 1). Question 1 is a global self-perceived health item (from excellent to poor) regarded as a valid synthesis of individuals' appraisals about their past, present, and anticipated health problems; for secondary analyses, question 1's five ordinal levels were collapsed into two dichotomous levels: 1) excellent, very good, and good, or 2) fair and poor. Three "days" questions measure poor physical health (question 2), poor mental health (question 3), and activity limitation resulting from poor physical or mental health (question 4) in the past 30 days. The sum of the responses to the second and third questions yields an "overall unhealthy days" measure that estimates the overall number of recent days when physical or mental health was not good with the restriction that the total number of days does not exceed 30 days. For example, a person who reports 4 physically unhealthy days and 2 mentally unhealthy days is assigned a value of 6 unhealthy days; someone who reports 30 physically unhealthy days and 30 mentally unhealthy days is truncated at the maximum of 30 unhealthy days to maintain the same timeframe as that of its components. Based on prior research with the CDC HRQOL-4 (9), we operationalized "frequent distress" using a cutoff value of 14 or more days when the patient described their mental or physical health as "not good." Conceptually, a 14-day "frequent distress" cutoff was deemed meaningful because this interval corresponds to the timeframe used by accepted taxonomies (44) for establishing mental distress (for example, major depressive episode) highly comorbid with IBS. Empirically, a cutoff point of 14 unhealthy days is regarded as a meaningful demarcation because it corresponds to the upper 10% to 15% of distribution of the general population for each of the HRQOL CDC indices (45).

In this study, 10 items supplement the CDC HRQOL-4: five questions about the existence, the main cause, the duration of any current activity limitation, and the need for help with activity-related personal and routine care, and five symptom-related questions about the number of recent days of pain, depression, anxiety, sleeplessness, and vitality. Together, the four core items and 10 supplemental items are referred to as the CDC HRQOL-14. In comparisons with longer standardized health status measures (e.g., SF-36), the CDC HRQOL demonstrates acceptable construct, criterion, and known-groups validity for healthy adults as well as adults with chronic health conditions and disabilities (12,46). Retest reliability at an average of 2 weeks, as estimated by intraclass correlation coefficients, is good (0.57–0.71) for the "days" questions of the CDC HRQOL (47). Reliability is slightly higher for overall "days" (0.75) than either mentally (0.67) or physical ill days questions (0.71), suggesting that the summary measure is a more consistent index of HRQOL than its components (47).

Global Assessment of Improvement
Overall relief of gastrointestinal symptoms was measured at posttreatment using a validated global improvement rating scale that ranged from –100 = substantial worsening to zero (no change) to 100 (substantial improvement) (48).

Statistical Methods
After conducting descriptive analyses, we analyzed the relationships between each of the quality-of-life measures first using Pearson product moment (zero-order) correlations. The second set of analyses involved partial correlations to examine the independent relationship between quality-of-life measures while controlling for personality variables (neuroticism, somatization).

In comparing mean overall unhealthy days for the study patients with IBS with mean overall unhealthy days for various subgroups of the general BRFSS population, we used direct standardization to adjust for the potentially confounding effects of sex. Sex is potentially confounding because the study patients with IBS were predominantly women, whereas the comparison BRFSS subgroups were more equally distributed by sex, and women in the BRFSS general population report more overall unhealthy days than men.

Therefore, we standardized the IBS patients' average overall unhealthy days directly to the BRFSS population using a two-step process: 1) calculating average overall unhealthy days separately for male ("male IBS unhealthy days") and female ("female IBS unhealthy days") patients, and 2) calculating a weighted average overall unhealthy days by applying as weights to these means the proportions of men (0.482) and women (0.518) in the standard population (1993–1997 BRFSS respondents) using the following formula:

Weighted average = 0.482 * male IBS unhealthy days + 0.518 * female IBS unhealthy days.

Descriptive Analyses
Eighty-three percent of the study patients with IBS were women, and 88% were white (Table 1). Their average age was 46 (standard deviation [SD] = 14.3) years old, and most had received education beyond high school. Almost 60% were currently married, 20%, never married, and 17% divorced. Their mean score on the Global Severity Index (GSI) of the Brief Symptom Inventory was 0.46, which corresponds to T-scores of 57 (SD = 9.8. female) and 60 (SD = 11.8, male) for adult nonpsychiatric norms. Twenty-seven percent of the patients (n = 26) reported past physical abuse, sexual abuse, or both.


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  		TABLE 1. Irritable Bowel Syndrome Sample Characteristics

 

Female (n = 86) patients with IBS reported an average of 12.5 (SD = 10.7) physically unhealthy days, 10.0 (SD = 9.6) mentally unhealthy days, 17.9 (SD = 11.8) overall unhealthy days, and 6.5 (SD = 7.8) recent activity limitation days. Male (n = 18) patients reported an average of 8.7 (SD = 10.5) physically unhealthy days, 8.4 (SD = 10.9) mentally unhealthy days, 12.8 (SD = 11.1) overall unhealthy days, and 3.0 (SD = 5.4) recent activity limitation days.

We also explored number of overall unhealthy days in relation to clinical variables regarded as important to IBS (bowel habit type, psychopathology, abuse, symptom severity). Constipation-predominant patients with IBS reported significantly more mentally unhealthy days (mean = 13.1, SD = 9.8) than diarrhea-predominant patients with IBS (mean = 6.8, SD = 8.3; p < .05), but not alternating patients (mean = 9.3, SD = 9.6). Bowel habit types did not differ with respect to overall unhealthy days or physically unhealthy days. Patients with clinical levels of distress (GSI T-score> = 63, 32) reported significantly more overall unhealthy days (mean = 25.3, SD = 9.1) than patients with nonclinical level of distress (mean = 14.7, SD = 11.1; p < .001). Similarly, patients with past abuse reported significantly more unhealthy days (mean = 21.0) than nonabused patients (14.1 days; p < .05). Patients whose symptoms the study gastroenterologist classified as severe reported more unhealthy days (mean = 20.0, SD = 10.3) than patients with moderate symptoms (mean = 11.5 days, SD = 11.3; p < .001). Patients with severe IBS symptoms reported twice the number of activity limitation days (mean = 8.1, SD = 8.7)) as moderately severe patients (mean = 4.0, SD = 5.7; p < .05).

Fifteen percent reported that their health limited their activities on 14 or more days in the past 30 days, although 64% reported some activity limitation. Forty-six percent attributed their major cause of activity limitation to IBS. The most common nongastrointestinal cause of activity limitation (15%) was musculoskeletal complaints (e.g., back, neck problems). Patients who identified IBS as their main cause of activity limitation reported 21.0 (SD = 9.8) overall unhealthy days during the previous 30 days, whereas those whose main cause of activity limitation was a nongastrointestinal health problem reported 17.7 (12.1) overall unhealthy days. The 36% of the sample who denied that health "in any way" limited their usual activities nonetheless averaged 11.6 unhealthy days (SD = 11.6).

Because the state-based BRFSS has administered the CDC HRQOL-4 since 1993 to over 1.2 million adults, its archival data allows a comparison of the perceived burden of IBS to that of those reporting risky behaviors, chronic diseases, and disabilities (Fig. 2). IBS patients reported more overall unhealthy days (mean = 15.4) in the 30 days before testing than individuals with arthritis, diabetes, and heart disease/stroke. Female patients with IBS reported more unhealthy days than women with breast cancer and class III obesity (body mass index ≥40 kg/m2). Furthermore, patients with IBS reported three times the number of unhealthy days and four times the number of activity limitation days as the average BRFSS respondent (mean unhealthy days = 5.3, mean activity limitation days = 1.7). Patients who identified IBS as the main cause of their activity limitation reported more activity limitation days (7.5 days) than BFRSS respondents with arthritis, diabetes, hypertension, and breast cancer. Compared with the average BRFSS respondent, patients who identified IBS as their major activity limitation reported 7.8 more days of pain, 7.4 more days of depression, 10 more days of anxiety, 8 more days of insufficient sleep or rest, and 14 fewer days of vitality in the 30 days preceding assessment. Their number of sleepless days (15.5 days) exceeded that of BFRSS respondents whose main cause of activity limitation was arthritis (9 days), cancer (11 days), or depression/anxiety (13 days). Patients with IBS reported more anxiety days (15.2 days) than BRFSS respondents whose main cause of activity limitations was arthritis (8 days) or cancer (11 days).


Figure 220
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  		Figure 2. Mean unhealthy days as a function of IBS and other health characteristics. All data except IBS based on 1993–1999 BRFSS, selected states, age-adjusted.

 

Zero-Order Correlations
The magnitude of the associations among the CDC HRQOL-4 and other measures reflected in Pearson's correlations was moderate (Table 2). Correlations between overall unhealthy days of the CDC HRQOL-4 and the PCS and MCS scores of the SF-36 were r = –0.43 and r = –0.59, respectively (p < .001). Similarly, significant correlations (p < .001) were found between the activity limitation days and the PCS (r = –0.50) and MCS scores (r = –0.37). Correlations between the IBS-QOL and the CDC HRQOL-4 scales were –0.52 for overall unhealthy days and –0.46 for activity limitation days (all p's < .001). Pain ratings correlated with all three quality-of-life measures. Except for the correlation between activity limitation days and the MCS score of the SF-36 (r = –0.37), all associations between the CDC HRQOL-4 and other quality-of-life measures satisfied Ware et al.'s definition of "substantial" zero-order correlations (r = 0.40 or greater [20]).


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  		TABLE 2. Correlations and Partial Correlations (Controlling for Neuroticism and Somatization) Between Study Variables

 

Partial Correlations
To identify whether significant zero-order correlations were independent of personality variables that influence the perception and reporting of HRQOL (21,49), we computed a series of partial correlations to remove all variance accounted for by somatization and neuroticism. Although the magnitude of correlations diminished across the quality-of-life measures, most retained their statistical significance (Table 2). In one instance (association between the PCS and IBS-QOL), the strength of the correlation (r = 0.27) dropped below our a priori criterion level of acceptability (0.30). Associations between the SF-36 PCS and HRQOL-4 total scores (unhealthy days, r = –0.38; activity limitations days, r = –0.46) decreased but remained significant (p's < .001) and above the acceptability criterion. The correlation between overall unhealthy days and SF-36 MCS (r = –0.44) remained moderately strong after control variables were held constant. The correlation between MCS and activity limitation days remained statistically significant but fell below the acceptability criterion (r = –0.25).

The association between total McGill score and the two HRQOL-4 summary scores remained significant at the 0.001 level but diminished in strength when the effects of neuroticism and somatization were controlled. Controlling for the effects of neuroticism and somatization decreased the strength but not the significance of the association between both HRQOL-4 indices and current pain VAS. In contrast, controlling for neuroticism and somatization decreased the association between current pain VAS and IBS-QOL to nonsignificance (r = –0.09). Generally speaking, the relationships between the HRQOL measures used in IBS research and the CDC HRQOL-4 are largely independent of neuroticism and somatization.

Sensitivity to Change
Repeated-measure analysis of variance was conducted to assess changes in HRQOL from pretreatment to posttreatment for the patients who underwent cognitive therapy. Compared with an average of 17 overall unhealthy days before treatment, cognitive behavior therapy participants (whose demographic characteristics did not differ from those of the whole sample) displayed significantly fewer (13) overall unhealthy days after treatment (F [1, 53] = 5.75, p < .05). A 4-day difference amounts to an average of one fewer unhealthy days per week after cognitive behavior therapy. CDC HRQOL change scores for unhealthy days (pretreatment unhealthy days – posttreatment unhealthy days) were significantly associated with global improvement in gastrointestinal symptoms as assessed by the patient (r = –0.36, p < .01) and a blind assessor, the study gastroenterologist (r = –0.28, p < 01). Patients who reported (or were rated as achieving) greater improvement in gastrointestinal symptoms after treatment also reported less QOL impairment (fewer unhealthy days).


   DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 DISCUSSION
NOTES
 REFERENCES
 
We sought to assess the merits of the CDC HRQOL-4 as a screening measure of overall HRQOL in patients with moderate-to-severe IBS. A conservative test of the CDC HRQOL-4 would require evidence that it 1) reflects the symptom burden of physical and mental problems and disability associated with IBS; 2) correlates significantly with established measures of QOL used in previous IBS research; 3) is acceptable to patients and simple for clinicians to administer, calculate, and interpret; and 4) yields a meaningful quality-of-life profile that is responsive to treatment and unobscured by personality variables that influence the perception and reporting quality of life. With respect to patient acceptability, the four items of the CDC HRQOL-4 can be completed more quickly (<1 minute) than either the SF-36 (10–15 minutes) or the IBS-QOL (10 minutes). The CDC HRQOL-4 does not require complicated scoring algorithms to derive a quality-of-life profile. Because the CDC HRQOL-4 has continuous, cardinal, and bounded (range, 0–30 days) mathematical properties, its metric is concrete and intuitive. In this respect, the CDC HRQOL-4 has advantages over other quality-of-life instruments that have been described as difficult to interpret and of limited practical value (5,50). The CDC HRQOL-4's unit of analysis is time-referenced (30 days) and therefore lends itself to the study of health-related quality of life, regarded as an inherently time-related phenomenon (9). Gauging the burden of IBS in terms of number of days has three additional advantages. First, a specific temporally defined unit is compatible with key economic concepts (e.g., cost-utility) featured in cost-effectiveness research (51). This feature may confer on the CDC HRQOL-4 an advantage over other widely used quality-of-life measures that cannot easily be used in either cost-effectiveness or cost-utility analyses (52). Second, a continuous, time-referenced measure may increase our understanding of how quality of life varies with temporally unstable phenomena relevant to IBS such as changes in primary bowel habit, environmental conditions, hormonal activity, and seasonal changes. Third, a face-validated, psychometrically sound measure of HRQOL index expressed in terms of number of healthy days can provide guidance for healthcare allocation decisions regarding the evaluations of new therapies for reimbursement and formulary listing.

Comparing average overall unhealthy days and activity limitation days in patients with IBS with those from adult BRFSS participants with other chronic medical conditions from 1993 through 1997 shows dramatic differences. Average overall unhealthy days among patients with IBS approximated that in patients with cancer and exceeded that in those with arthritis, diabetes, heart disease/stroke, or obesity. In those reporting activity limitation, patients with IBS report more activity limitation days than patients with arthritis and 10 times the number of activity limitation days as adults reporting no activity limitations. Notwithstanding the brevity of the CDC HRQOL-4, these data parallel the findings of studies showing that the health-related quality of life (measured with the SF-36) among patients with IBS is comparable to individuals with other chronic illnesses (4,5,14). In short, the CDC HRQOL-4 appears to capture the cumulative burden of physical and mental problems and disability associated with IBS.

The CDC HRQOL-4 also appears to detect the relationship between poor quality of life and other clinical variables (bowel habit type, symptom severity, abuse, psychological distress) associated with more severely affected patients with IBS. Patients with more severe IBS symptoms reported more unhealthy days and more activity limitation days than less severely affected patients with IBS. Like Trillish et al. (53), we found no differences in overall quality of life across patients with different bowel habits. However, constipation-predominant patients reported significantly more mentally unhealthy days than diarrhea-predominant patients. To our knowledge, these are the first data documenting differences in quality-of-life impairment as a function of predominant bowel habit type.

Although patients who reported more activity limitation days described worse well-being on the IBS-QOL, IBS was not necessarily the cause of poorer quality of life. Indeed, less than half of the sample (46%) identified IBS as the major cause of activity limitations. The second most common cause of activity limitation was musculoskeletal problems. These findings complement the work of other researchers who have highlighted the importance of extraintestinal symptoms of patients with IBS (54,55). Although the influence of extraintestinal symptoms on objective health outcomes is established, their relationship to quality of life has been difficult to discern. Part of the problem may relate to the logic underlying the construction of generic and condition-specific quality-of-life instruments. Condition-specific measures assume that the condition for which the patient seeks treatment is the primary cause of diminished quality of life. Condition-specific measures thus are by definition not explicitly concerned with comorbid physical symptoms or the extent to which they affect quality of life. Given the prevalence of extraintestinal conditions in IBS that may compromise quality of life (55), it is unclear whether or not condition-specific measures such as the IBS-QOL reflect the full effect of IBS on the patient's HRQOL.

If condition-specific measures have limited scope in assessing the range of HRQOL, generic measures suffer from their own generality. Because generic quality-of-life measures are designed to facilitate comparisons across diagnostic conditions and interventions, these measures emphasize the effect on HRQOL of multiple functional domains (physical and psychological health, social relationships, function, subjective well-being, pain) but deemphasize condition-specific causes of burden of illnesses Reducing medical problems to two overarching health domains prohibits detailed analyses of the relative impact that multiple health complaints impose on quality of life. Illnesses such as IBS, which commonly occur with other medical conditions, expose the limitations of generic quality-of-life measures. For example, one cannot confidently discern whether IBS or another comorbid complaint or both affect the generic measure. In quality-of-life research using generic measures, the cause of quality-of-life limitations are presumably the result of the primary medical diagnosis. Echoing the work of Speigel et al. (1), our data indicate that this assumption is not necessarily accurate. Fifteen percent of our IBS sample explicitly identified an extraintestinal medical problem as the cause of activity limitations. Two features of the CDC HRQOL-4 may prove useful in clarifying quality of life in patients with IBS in patients with medical comorbidities. Unlike condition-specific measures, the CDC HRQOL-4 elicits judgments of self-perceived health (question 1), a sensitive measure of medical comorbidity (56). Unlike most generic measures, the CDC HRQOL modules include a question asking respondents to identify the major health problem that limits their daily activities. Such descriptive information, albeit coarse, may prove useful in teasing out the relative symptom burden of IBS and comorbid medical illnesses.

Our findings address an important but largely neglected question of "what do quality-of-life scales really measure?" In general, psychometric validation studies of quality-of-life measures have relied heavily on zero-order correlations (57) to establish their psychometric properties. This approach is potentially problematic because it does not rule out the possibility that any significant zero-order association between quality-of-life scales is a correlated effect of a third variable. If so, zero-order correlations do not necessarily support an instrument's ability to measure underlying HRQOL. Indeed, personality characteristics, particularly neuroticism and somatization, have been found to influence the reporting of HRQOL (49,58). Subjective well-being measures of quality of life seem especially vulnerable to their influence (21). Although it is unclear whether personality characteristics influence "true levels" of HRQOL, patients' appraisal of HRQOL levels, or both, these characteristics appear to play a larger role in HRQOL assessment than many quality-of-life researchers have acknowledged. In this study, controlling for neuroticism and somatization diminished the strength of correlations between CDC HRQOL-4 and other quality-of-life and pain measures. This effect cut across all quality-of-life measures but was strongest for subjective well-being measures (e.g., unhealthy days, IBS-QOL, SF-36 Mental Component Summary), particularly the IBS-QOL. Indeed, its correlation with pain (McGill) was statistically nonsignificant after the variance accounted for by distress variables was held constant. On the other hand, any diminution in the magnitude of the associations involving the CDC HRQOL-4, however, did not render them statistically nonsignificant. The general pattern of these data largely argues against the conclusion reached by Halder et al. (27) that health-related quality of life and somatization are essentially redundant in individuals with IBS.

These data need to be interpreted in light of possible limitations. Because most of our data are cross-sectional and correlational, we do not intend to suggest that the findings demonstrate causal relationships among study variables. At best, findings can be construed as suggesting possible causal relationships that could be confirmed through longitudinal studies. By relying largely on self-report data, some correlations may reflect shared method variance. Study patients were treatment-seeking individuals willing to enroll in a randomized, controlled trial of two psychological treatments. Therefore, our findings do not necessarily generalize to primary care settings or community populations representative of most patients with IBS. Because BRFSS data excludes adults living in institutional settings who are more likely to have severe chronic illnesses, our comparison data may underestimate the symptom burden associated with IBS. Alternatively, by using a comparison group of community residents, we may have overestimated the symptom burden of IBS relative to that of a reference group of chronically ill patients found in tertiary care settings. We recognize that there is no "gold standard" for measuring the relative symptom burden of a disease. Our approach, although imperfect, follows the practice of other IBS researchers who have operationalized illness burden by comparing the health characteristics of community samples against patients with IBS on a common qualify-of-life index (e.g., SF-36 scores) (3–5,14).

Although our data empirically support the use of CDC HRQOL-4 with patients with IBS, the CDC HRQOL-4 is a screening measure not designed to replace generic or condition-specific quality-of-life measures. The CDC HRQOL modules do not provide either the rich and varied clinical information of the IBS-QOL or normed comparison data or multidimensionality of the SF-36. Of course, these features are of limited value as long as practical barriers prohibit clinicians from implementing routine quality-of-life assessment in busy clinical practice settings. Spiegel et al. (1) regard these barriers as so insurmountable that they recommend shifting focus from assessing quality of life per se to its clinical predictors (e.g., anxiety, sleep, hopelessness, fatigue, sexual dysfunction). We are not confident that this approach is any less cumbersome than formally assessing quality of life. Furthermore, the assessment of a set of statistically derived clinical predictors, however concise, does not explicitly measure HRQOL and therefore falls short of guidelines recommending routine HRQOL assessment (6). If, as Gralnek et al. (3) recently wrote, the measurement HRQOL of patients is truly "essential" for understanding IBS, its promise may be more fully realized with brief, validated measures that balance informational value with parsimony and efficiency. Measures such as the CDC HRQOL-4 may offer clinicians and researchers an important tool for capturing patients' experience, informing decision-making, strengthening patient-provider relations, and enhancing the delivery of care.


   NOTES
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 DISCUSSION
 NOTES
REFERENCES
 

Preparation of this paper was supported in part by National Institutes of Health grants DK-54211 and DK-67878.

DOI:10.1097/01.psy.0000204897.25745.7c


   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 DISCUSSION
 NOTES
 REFERENCES
 

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