Affiliations of authors: Cancer Research Center of Hawaii, University of Hawaii, Honolulu, HI (CCG); Rollins School of Public Health, Emory University, Atlanta, GA (JL); School of Medicine, Johns Hopkins University, Baltimore, MD (CFS)
Correspondence to: Carolyn C. Gotay, PhD, Cancer Research Center of Hawaii, University of Hawaii, 1236 Lauhala Street, Honolulu, HI 96813 (e-mail: cgotay{at}crch.hawaii.edu).
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ABSTRACT |
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INTRODUCTION |
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As part of its Quality of Cancer Care Initiative, the U.S. National Cancer Institute (NCI) convened the Cancer Outcomes Measurement Working Group (COMWG) in 2001 to assess the current state of the science and to provide recommendations for future research to improve the assessment of these patient-reported outcomes. The COMWG was made up of 35 scientists from the United States, Canada, and the Netherlands; its members included medical oncologists, psychologists, economists, biostatisticians, nurses, health services researchers, and cancer survivors, with members from government agencies, universities, and cancer centers (see Appendix).
The COMWG focused on three primary outcomesHRQOL, patient needs and satisfaction, and economic burdenin the four cancers that affect the largest numbers of individuals in the United States: breast, colorectal, lung, and prostate. The group considered outcomes measurement across the entire spectrum of cancer prevention, detection, treatment, survivorship, and end-of-life care. COMWG members provided critical review and discussion of current literature in prespecified topics and identified areas in which more work is needed. The specific research questions that COMWG members were asked to address were as follows: What are the current best practices and recommendations for the future in assessing the three outcomes (HRQOL, satisfaction, economics) in the four cancers (breast, colorectal, lung, prostate) across the continuum of care? What are the definitions and conceptual models for outcomes measurement? What are the methodologic issues and challenges (psychometric, statistical, study design, and execution)? What are different perspectives on and uses of cancer outcomes data?
Methods used to address these questions included extensive searches of the research literature, searches of published and unpublished reports of government agencies, new analyses of existing datasets, and interviews with focus groups. Because the COMWG was not a federal advisory committee or consensus panel, its findings reflect only the individual judgments and perspectives of its members. Full and detailed accounts of the analysis of specific topics addressed by COMWG, including information about the specific methods used, have been published elsewhere (1).
In this commentary, we highlight some of the overarching themes that emerged from our analysis of the COMWG effort. Our commentary should not be construed as reflecting a consensus of the COMWG membership. Most of our discussion focuses on HRQOL because this area has received more attention in the research literature than the other outcomes; however, we include the other outcomes when appropriate. We focus on 1) the quality of the tools currently available to measure HRQOL in cancer research, 2) methodologic accomplishments and promising directions, and 3) use of HRQOL measures and interpretation of findings. We conclude by identifying research priorities for moving the field forward.
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THE QUALITY OF CURRENT TOOLS USED TO MEASURE HRQOL OUTCOMES IN CANCER |
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Application of the MOT framework to the literature about use of HRQOL instruments gave rise to the following inferences:
1) Despite skepticism by some critics, assessing HRQOL in a research context is feasible. Patients do not resent being asked about personal aspects of their lives, and they do not object to using numerical, somewhat abstract scales to indicate their responses. HRQOL assessment can be incorporated in clinical protocols without placing undue burdens on either patients or clinicians. HRQOL assessment can be accomplished in the context of clinical trials, the application in which the largest amount of research has focused to date; in observational studies of treatment outcomes (13); and in descriptive studies of the impact of cancer in selected populations (14).
2) It is widely (although not universally) agreed that HRQOL is an unobservable, or "latent," construct that acquires operational meaning only through an appropriately specified and estimated psychometric measurement model. A key aspect of HRQOL assessments (as well as patient reports, evaluations of care, and needs assessments) is that these outcomes reflect the patient's perspective. There is also general agreement that these outcomes should be regarded as multidimensional constructs. In particular, HRQOL nearly always includes measures of physical and mental/emotional health, although there is less consensus about whether additional domains, such as social functioning, spiritual well-being, symptoms, and role functioning, are essential to HRQOL. In addition, specific domains may be particularly relevant in a limited set of circumstances (e.g., sexual functioning in prostate cancer, fertility concerns in survivorship). Measures of patient satisfaction or care experiences frequently include domains such as provider communication and access. The domainsthat is, the general categoriesof patient needs tend to be much less clearly specified than those of HRQOL. The more common measurement strategy is therefore the assessment of specific and well-defined needs, as opposed to broader domains.
3) Numerous HRQOL questionnaires are currently available that have been developed with careful consideration of most of the MOT criteria (2). Some of the most common approaches to HRQOL assessment include (a) generic measures, which are designed to be used in any disease group or a general population; (b) general cancer measures, which have been developed for use across cancer types; (c) cancer-specific measures, which are designed to be used in specific cancers; (d) general cancer core questionnaires supplemented with cancer-specific modules, which combine the general cancer and cancer-specific approaches; and (e) targeted, unidimensional measures, which focus in depth on specific aspects of HRQOL (including symptoms like pain, nausea, and fatigue) and that can be used alone or in combination. Global and preference-based measures (i.e., those that incorporate comparisons of the values attached to different health states) are also reported, although less frequently. Extensive data support the reliability and validity of many of these questionnaires, and recent attention has also focused particularly on the questionnaires' responsiveness, interpretability, and cultural and language adaptations [see Aaronson (15)]. In contrast, the methodological development of questionnaires to assess patient perceptions of care (including satisfaction) and needs is less mature (10,11).
4) Outcomes measurement can be applied across the continuum of cancer prevention, detection, survivorship, and care. As Mandelblatt and Selby (16) point out, individual assessments can be used in cancer prevention and screening, where the emphasis is on not harming healthy individuals (as opposed to treating patients with cancer). Zebrack and Cella (12) note that outcomes assessment is equally applicable in cancer survivorship, because the impact of cancer and its treatment does not cease when treatment ends and these long-term effects of cancer have important consequences on functioning and well-being. Finally, as Ferrell (7) notes, when patients are terminally ill, comfort and well-being should be the primary focus.
5) Although there is some agreement in the literature about what domains should be included in HRQOL, there is less consensus about which aspects of these domains should be measured. Ferrans (17) distinguishes between different kinds of HRQOL questions that patients may be asked: questions about objective conditions (e.g., did you go for a long walk today?), questions about perceived status (e.g., could you go for a long walk today?), and evaluation questions (e.g., how satisfied are you with your physical functioning today?). Litwin and Talcott (6) and Darby (10) make similar distinctions regarding questions about symptoms and patient care experiences, respectively. These varying questionsall of which are found in different HRQOL questionnairesmay not necessarily yield consistent findings. For example, patient evaluations may be heavily affected by factors such as expectations, previous experience, and predispositions, whereas these factors may not affect responses to questions about objective conditions. The interrelationships among these different ways of asking questions about HRQOL have not been examined in depth.
6) The content validity of available HRQOL instrument(s) should be enhanced to optimize their use in particular populations. For example, Moinpour and Provenzale (4) concluded that social functioning is assessed inadequately in HRQOL measures applied to colorectal cancer patients undergoing treatment. Zebrack and Cella (12) found that current multidimensional HRQOL measures may not capture elements important to cancer survivors, such as fear of recurrence or chronic physical compromise. Williams (18), a prostate cancer survivor, believes that current HRQOL instruments fail to capture the depth of suffering faced by cancer patients and their families.
7) A number of different HRQOL questionnaires exist, yet few have been compared directly. This situation raises the proverbial question, "What's the best HRQOL questionnaire?" Several analytic methods that are currently being developed, particularly item response theory (IRT) modeling, could make this question moot in the future. IRT modeling is described in more detail below; in brief, IRT-based item banks (that is, compilations of questions) are intended to facilitate the development of computer-adaptive assessments. These assessments would draw from the constellation of available items from many existing HRQOL questionnaires to identify and sequence the items that are most appropriate for each respondent. In theory, IRT applications have the potential to dramatically reduce the need for single (i.e., traditional, fixed-item) instruments.
For the time being, however, COMWG members did not feel that any single HRQOL scale was best for all purposes, because each study requires measures that are appropriate to its distinct hypotheses and patient population. Our summary suggestions for questionnaire selection, which are consistent with the COMWG analyses, are as follows:
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METHODOLOGIC ACCOMPLISHMENTS AND PROMISING DIRECTIONS |
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2) One of the biggest methodologic challenges in cancer HRQOL research is missing data. If a scheduled HRQOL assessment is missed, the required data cannot be retrieved accurately at some later point or extracted from the medical records. Large amounts of missing data threaten the interpretation of research studies and in fact have been responsible for closing clinical protocols in the past (20). However, considerable progress has been made in this area. Fairclough (21) discusses a number of techniques to avoid or minimize missing data, including designating responsible staff to manage the HRQOL data collection, training data collectors and study participants, budgeting adequate resources for monitoring and patient follow-up, and considering the adoption of multiple modes of survey administration (e.g., paper-and-pencil self-assessments, in-person interviews, telephone surveys, or electronic [including web-based] approaches). Some of these technologies are just becoming available in the clinical setting and thus their use is only beginning to be reported in the scientific literature.
3) Approaches to analyzing HRQOL data have undergone considerable development. Although it is often thought that HRQOL analyses are qualitatively different from biomedical analyses, Sloan (22) argues that the statistical analysis of HRQOL and other patient-reported outcomes poses no greater problem, fundamentally, than is encountered with more traditional biomedical measures. He suggests that it is vital to have a clear statistical modeling plan specified in advance, to pursue complex statistical modeling approaches only after careful basic analyses have been completed, to conduct sensitivity analyses to examine the robustness of study findings as a routine matter, and to present findings clearly and transparently, emphasizing not only summary statistics but graphical displays and other approaches to reveal important variations within the sample.
4) New approaches to questionnaire development and analysis hold considerable potential for addressing many conceptual and practical concerns. In particular, the application of IRT to the study of HRQOL is very promising. Although IRT is long established in educational testing research (2325), it is only recently being applied in the HRQOL arena. IRT provides an alternative perspective to classical test theory (CTT), the more standard approach for assessing and evaluating HRQOL and other patient-reported outcomes that involve latent-variable constructs (i.e., those that can be inferred through indicators but cannot be observed directly). A CTT approach to estimating an individual's HRQOL level is typically based on the sum of survey item responses, whereas an IRT approach makes use of the pattern of item responses because each item is assumed to convey specific, differentiated information about the individual's HRQOL level on a particular unidimensional construct.
In essentially tailoring the questionnaire to the individual, IRT modeling offers a number of potential advantages over CTT. First, IRT allows more fine-tuned measurement across the HRQOL continuum, is more efficient, and poses less respondent burden. As noted, it also may lead us to the point that researchers need not choose among competing HRQOL questionnaires, because it is possible that all such items could be pooled, given weights, and even administered as part of a computer-adaptive testing protocol. In such an approach, items would be selected sequentially and strategically based on the respondent's responses to previous items. IRT modeling also enables a statistically rigorous examination of whether a given instrument performs the same or differently across cultures, geographic borders, and population subgroups through analysis of "differential item functioning."
Considerable work still needs to be done before IRT can be used in HRQOL assessment. Some concrete issues, such as intellectual property conflicts, may arise with item banking (26). In addition, the multidimensionality of HRQOL can pose challenges to IRT measurement models, which assume unidimensionality, in instances where a summary measure (single index) is needed. It should also be noted that CTT imposes a similar unidimensionality assumption. Also, IRT's application may be limited unless the technology to support these methods (e.g., computer-adaptive technology) is available. Nevertheless, there was virtual consensus among COMWG participants that IRT provides the most (if not the only) sound theoretical basis for item banking, computer-adaptive testing, cross-walking scale scores (that is, comparing items from different questionnaires) via item linking, and investigating differential item functioning. This area is developing fast [for an update, see reference (27)].
5) Additional analytic approaches, such as structural equation modeling and Bayesian analysis, may be useful in HRQOL research. Structural equation modeling may offer a useful platform for exploring issues related to conceptual models of HRQOL. This approach facilitates the development of causal models that depict relationships among sets of survey items, scales and subscales, other patient-reported (e.g., symptoms) and biomedical (e.g., toxicity) outcomes, and exogenous factors, such as respondent age, race, sex, and educational level. To date, there have been comparatively few applications of structural equation modeling to HRQOL (28); future analysis will clarify whether this approach will help to identify causal indicators for HRQOL.
As O'Brien (29) argues, Bayesian statistical modeling has been underused in HRQOL research to date. Such techniques may be particularly useful in cost-effectiveness and cost-utility analyses that take a lifetime perspective.
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USE OF HRQOL ASSESSMENTS AND INTERPRETATION OF FINDINGS |
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2) There is much more research available about HRQOL in some cancers than in others. This situation affects the conclusions that can be drawn.
In breast cancer, many studies that include HRQOL assessment have been published, partially due to the relatively high prevalence of this diagnosis and breast cancer survivors. Ganz and Goodwin (3) concluded that younger patients and those with more advanced disease report more distress, that survivors generally have HRQOL equivalent to that in control groups, that HRQOL improves in the year postdiagnosis and worsens with recurrence, and that psychological interventions confer substantial benefits. These authors also found, surprisingly, that HRQOL in breast cancer patients receiving adjuvant chemotherapy has been studied only infrequently and that HRQOL data have not contributed to the interpretation of most of the biomedical breast cancer treatment studies reported to date.
The analyses for each of the other three cancer sites (lung, colorectal, and prostate cancer) all yielded somewhat different conclusions from the breast cancer analyses and from each other. There was considerably less literature available for review in lung and colorectal cancer than in breast and prostate cancer. The existence of relatively few HRQOL studies in these cancers may partially reflect the fact that only 39% of colorectal cancers and 16% of lung cancers are diagnosed when they are still localized (33). HRQOL assessment in more advanced disease presents distinct methodologic challenges from its assessment in localized disease, particularly with respect to missing data in prospective studies. In both lung and colorectal cancer, studies of both primary and adjuvant treatments and their association with HRQOL are common. Earle and Weeks (5) noted that, in lung cancer, health care professionals believe that patients' HRQOL is worse than the patients think it is. In prostate cancer, a disease for which the current therapeutic modalities for early-stage disease have long-term consequences for sexual and bladder function, measures of impotence, incontinence, and other symptoms were frequently reported (6). Litwin and Talcott (6) noted that HRQOL data have shown that patient impairments in these areas are much more common than clinicians have realized.
3) The interpretation of HRQOL findings is limited by the absence of widely accepted models to define HRQOL and to specify predictive and correlated variables. As Ferrans (17) discusses, HRQOL has yet to be consistently defined; consequently, different and sometimes competing definitions may be used. Darby (10) points out that the same is true for patient satisfaction. Erickson (9) observes that even when two measures purport to assess the same domains, they may use very different items to measure what is theoretically the same concept. Because HRQOL questionnaires vary widely in their domains and items, much confusion remains as to what HRQOL really is.
The conceptual underpinnings of measurement models also need additional attention. For HRQOL (and also patient perceptions of care and needs assessment), conceptual models are required that include a theory that specifies which domains are to be included in the HRQOL measurement model, the relationships among the various domains, the relative importance of the domains, and a causal pathway that clearly distinguishes causal from indicator variables [in the terminology of Fayers and Machin (28)] and that specifies the relationships between them.
One important factor that needs to be considered in such models is "response shift." As discussed by Schwartz and Sprangers (34,35), this phenomenon refers to how a patient's changing internal standards and values affect HRQOL ratings over time. As Ferrans (17) emphasizes, a deeper understanding of whether response shift influences HRQOL assessments in oncology could open the way to conceptual models that better account for the complex relationship between changes in relatively objective biomedical outcomes and more malleable HRQOL measures.
4) There is an emerging consensus for how to interpret HRQOL scores. Osoba (30), Sloan (22), and a recent series of meetings sponsored by the Mayo Clinic (36) have provided insights about clinical interpretability. Considerable progress has been made in terms of quantifying what patients perceive to be meaningful changes in HRQOL, as reflected in their scores on HRQOL questionnaires, and the extent to which such scores are associated with differences that make sense to clinicians. Osoba's evidence-based conclusion that a small, perceptible, and meaningful change in an HRQOL score appears to be about 7% of the full scale breadth (perhaps bracketed by 5% and 10%) is a genuinely surprising if not felicitous finding that bears ongoing investigation by anchor-based approaches, as he rightly emphasizes (30). Among such anchors should be those that have what we might term "decision significance," i.e., a relationship between observed changes in HRQOL scores and choices, real or hypothetical, made by patients or other decision makers (37).
5) The "value added" by HRQOL assessments, particularly in clinical trials with a survival endpoint, is not well understood. In a number of trials, HRQOL is the primary endpoint of the study; as such, HRQOL data provide the major indications of intervention efficacy in these studies. However, in trials whose primary endpoint is survival and for which HRQOL is a secondary endpoint, the contributions of HRQOL data are not always clear. If HRQOL and survival covary (e.g., if survival and HRQOL both increase), the HRQOL data may be regarded by some trialists as redundant. Given the significance of increasing survival for both clinicians and patients (38,39), HRQOL data may have a limited impact on study interpretation when survival differences are found. In the words of some COMWG members, "Survival trumps all."
In instances when HRQOL data do not covary with survival data, several explanations are possible (4,40). The HRQOL measurement tool may not have been not sensitive enough to detect real differences in patient well-being; the HRQOL measurement tool may not have focused on the right aspects of HRQOL; the timing of the HRQOL assessment may not have been appropriate to when patients perceived changes in HRQOL; the trial may have had methodologic flaws that affected the HRQOL data, such as small sample size or large amounts of missing data; or the (statistically significant) difference in biomedical outcomes did not in fact correspond to a clinical benefit (or harm) that was both perceptible and important to the patient, which would be consistent with the observation that there was no clinically meaningful change in HRQOL.
Given the multiple possible explanations for any set of findings, we believe that it is premature to conclude, based on clinical trials, that HRQOL data do or do not contribute to treatment decision making. Careful attention needs to be given to the selection of HRQOL measures for clinical trials and to understanding the relationships between and among the various outcome measures. In particular, the relationship between symptom assessment and HRQOL should be explored. This analysis is especially important considering that the Food and Drug Administration has based its regular approval of 13 out of 57 new cancer agents on the relief of tumor-specific symptoms (41).
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NEXT STEPS |
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Several kinds of future activities may facilitate this translation. These might include:
Reducing deaths and suffering due to cancer is a compelling and daunting challenge that is being pursued by a worldwide community of cancer researchers, providers, patients, survivors, families, caregivers, and volunteers. With basic and clinical scientific discoveries now accelerating the development of promising new interventions and with a heightened public and private focus on delivering quality cancer care to all who need it, there are good reasons to expect substantial and sustained progress in reducing the cancer burden. Through cancer outcomes assessment, we can monitor the progress being achieved at any point in time while conducting the research needed to inform decisions that will have a direct impact on reducing the burden over time.
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APPENDIX: MEMBERS OF THE NCI CANCER OUTCOMES MEASUREMENT WORKING GROUP, 20012004 |
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NOTES |
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The views expressed are those of the authors and do not necessarily represent the position of the National Cancer Institute.
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REFERENCES |
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Manuscript received April 20, 2005; revised August 26, 2005; accepted September 8, 2005.
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