The Gulf War Veterans Health Research Portfolio
As discussed in Chapter 1, the first of the three components in the charge to the IOM committee called for identifying questions important in evaluating the health and well-being of active-duty troops and veterans who were deployed to the Gulf War. Chapters 2 and 5 address the second component of the charge: to identify issues to be addressed in the development of study designs and methods that would be used to answer such questions. The third component of the charge to the committee was to develop a research design (or designs) that could be used to address such questions. Because these questions about the health of Gulf War veterans are diverse, efforts to address them in a thorough manner will require the application of various types of research and health measurement (e.g., population monitoring, treatment effectiveness, and clinical practice quality).
Research Portfolio to Guide Studies of the Health of Gulf War Veterans
In the committee's judgment, a single study cannot satisfy all information needs about the health of Gulf War veterans (and the various comparison groups noted in the questions in Chapter 1). The committee also recognizes that many completed studies have already made important contributions to our understanding of the problems affecting the health of Gulf War veterans and that other valuable studies are under way or will be undertaken. Various agenda-setting bodies are directing the flow of resources to these investigations. The committee believes, however, that the contributions of future individual studies will be enhanced by a mechanism to coordinate and link these studies. Others, such as the
Presidential Advisory Committee (PAC) (1996b), have also recognized the need for better coordination and oversight of the numerous studies.
Thus, the committee has responded to the task of developing a research design (or designs) that could be used to address questions regarding the health of Gulf War veterans by conceptualizing a "portfolio" of research activities. This portfolio encompasses an array of studies that could be conducted on a variety of topics, using study designs and population subgroups appropriate to the specific questions under investigation. An essential feature of the research portfolio is facilitating linkages across individual studies through the collection of a core set of key data elements, thereby allowing comparisons across all research. This idea is consistent with the observation of the PAC (1996b:31) that "when specific questions from different studies are aimed at obtaining the same information, then consistency [of questions] offers the advantage of allowing future inter-study comparisons."
The committee believes that this portfolio approach will, if implemented, provide a more effective basis for assembling the information needed to achieve a greater understanding of the longer-term health effects of service in the Gulf War. Moreover, the committee views the conceptual framework and the practical, methodological features inherent in the proposed research portfolio as a model that could be used by the Department of Veterans Affairs (VA) and the Department of Defense (DoD) to conduct similar studies of the health consequences of deployment to other conflicts (e.g., Somalia, Bosnia). In fact, the committee believes that inclusion of veterans of such conflicts in some of the studies conducted within the proposed research portfolio will provide a way of distinguishing between health consequences that are unique to the Gulf War and those that emerge from participation in any conflict.
Specifically, the committee recommends that multiple studies be initiated through a research portfolio with three components: population studies, health services research studies, and biomedical and clinical investigations.
Further, the committee recommends that a core set of data on health be collected in all studies and include measures of
- death and duration of life,
- functional status,
- health perceptions, and
These categories of measures reflect the five core concepts of health-related quality of life outlined in Chapter 3.
Research Approaches in the Portfolio
The committee envisions the research portfolio as providing a basis for developing the research agenda—that is, to plan, implement, and coordinate the variety of studies—needed to address diverse veterans' health issues. The portfolio encompasses three principal categories of research: population studies, health services research, and clinical and biomedical investigations. Figure 4-1 illustrates the research portfolio, with the horizontal bars representing the three major categories of research used to study the health of Gulf War veterans.
Population studies are conducted to measure and track levels and trends in health status and health outcomes, risk factors, the use of health services, and other health correlates (as described in Chapter 3) for entire populations, such as communities, or in the context of this report, the population of Gulf War veterans (and specific comparison groups). Such studies are also used to investigate the course of disease and illness. Data are often collected through surveys of statistically valid samples of the population.
Health services research is a multidisciplinary field that investigates the structure, processes, and effects of health care services (IOM, 1995). It may involve health status assessment to establish priorities, examine the effectiveness of health policies and programs, and allocate resources, using a variety of data sources. Within this category, the committee would include program evaluation, policy analyses, and health status assessments to select treatments and monitor individual patient outcomes (often typically with health data obtained from medical examination and testing).
Clinical and biomedical investigations are used to test the efficacy of diagnostic and therapeutic interventions. They are also used to examine the etiology of diseases and less well understood health problems such as those reported by Gulf War veterans.
In developing a research design (or designs) that could be used to address questions regarding the health of Gulf War veterans, the Committee decided to focus on the population studies level of the research portfolio. This conclusion was based on several considerations.
First, it is necessary to determine to extent to which the Gulf War veteran population experiences health problems. Such an overview is best obtained through a population monitoring study. Second, it is necessary to determine whether identified problems are unique to Gulf War veterans or are shared by other populations and, therefore, not specifically related to service in the Gulf War. Third, it is important to obtain information that will generate hypotheses that can guide more detailed studies at the two other levels of the research portfolio. In Chapter 5, the Committee describes in more detail a prospective cohort study—the Gulf War Veterans Health Study—that is intended to provide the population-based foundation for the research portfolio.
Dimensions of the Research Portfolio
Figure 4-1 illustrates three dimensions that characterize the range of studies that the committee sees encompassed by the research portfolio: scope of the studies in terms of coverage of the domains of health, level of detail at which studies address the domains of health and health correlates, and the time frame for studies.
Scope of Studies
Study scope is shown as ranging from general to specific on the vertical axis. Population studies fall at the general end of this general-to-specific axis. The prospective cohort study, described in Chapter 5, will cover the five domains of health discussed previously, that is, death and duration of life, impairment, functional status, health perceptions, and opportunity. From the prospective cohort study might emerge an epidemiological study to clarify the incidence, prevalence, and determinants of cognitive impairments among Gulf War veterans and comparison groups.
At the other end of this axis are clinical and biomedical investigations. These are studies in which health data may be the most person-specific because the studies are focused on more specific health or illness questions, often investigated, for instance, in clinical research of biological markers or randomized clinical trials (RCT). As one case in point: results from the prospective cohort study might indicate that fatigue is more prevalent among Gulf War veterans than among comparison populations. Thus, for patients with severe fatigue
problems, an RCT of physical therapy and conditioning might be given high priority. Another example is trials of new pharmacotherapeutic agents for use among patients with serious joint pain.
At an intermediate point in terms of scope are health services research studies. Such studies might address a wide variety of topics. With respect to quality of care provided to Gulf War veterans and other comparison groups for specific ailments or problems, a study could examine whether the process and/or outcomes of care differ among these groups. Similarly, one might investigate the cost-effectiveness of alternative interventions for managing Gulf War veterans and other patient populations with chronic fatigue syndrome. In addition, issues of timely access to appropriate, necessary care could warrant investigation; for instance, one might research whether veterans who participate in the VA or DoD Gulf War registries report better access to specialty care.
Level of Detail on Domains of Health and Health Correlates
The horizontal axis of Figure 4-1 represents the level of detail at which studies would address various domains of health and quality of life. For example, a population monitoring study that explores the prevalence and correlates of disability among Gulf War veterans may ask about limitation in physical activity (e.g., walking and performing basic activities of daily living), as well as a large number of additional domains. However, a clinical study of patients with a diagnosis of rheumatoid arthritis is likely to collect detailed information about both upper and lower body function but only core information about other domains such as cognitive function.
The third axis in this model, as shown in Figure 4-1, represents the time dimension of studies in the research portfolio. It is important to note that the length of time it takes to complete a study varies with the type of study conducted, therefore the time axis will show variation in depth. Among population studies, for example, a longitudinal cohort study with repeated administrations of the survey instrument will require a much longer time period than will a single cross-sectional study based on a one-time survey. Including time in the portfolio model also takes into account the possibility of selecting measurement strategies that incorporate time as part of their conceptual framework, such as in the quality-adjusted life year approach to health status and quality-of-life measurement.
Core Data Sets
The core set of measures for all three research approaches should include both measures of health, and likely correlates of health, as discussed in Chapter 3.
For comparisons between studies, each of these characteristics should be assessed using the same data collection instruments and methods. Individual investigators could choose to measure any of these characteristics in more detail, as fits the purpose of their studies. In the committee's view, adopting a common minimum set of measures will overcome some of the problems of interpreting Gulf War research findings.
Figure 4-1 illustrates the inclusion of core data sets in research portfolio studies with two shaded vertical columns. The first column represents data on individual and environmental characteristics, for instance, protective and dangerous environmental exposures. This also includes information on personal characteristics such as age, gender, and education, as well as selected information about occupation, socioeconomic status, and military service. The second column represents the core set of health measures. Conceptually, identical data within these two columns would be collected in any investigation carried out within any of the portfolio's three research approaches.
Thus, in addition to the core set of data on health identified in the previous recommendation in this chapter, the committee recommends that a core set of data on the correlates of health be collected in all studies. These data should include measures of individual and environmental characteristics that are associated with differences in health. Individual characteristics of interest include
- biology and life course,
- lifestyle and health behavior,
- illness behavior,
- personality and motivation, and
- values and preferences.
Environmental characteristics of interest include
- social and cultural,
- economic and political,
- physical and geographic, and
- health and social care.
For population studies (the top bar in Figure 4-1), the shaded vertical columns at the right-hand side of the bar show the core set of measures on health-related quality of life as being one of the more detailed sets of items. For clinical and biomedical investigations (the bottom bar), the core columns fall at the left-hand side of the horizontal bar, indicating that these measures are a small set of the totality of constituent domains included in clinical investigations. The two columns appearing in the health services research row are an intermediate position in the data collection strategy.
To link the studies of the research portfolio to national-level data for the general population, it would be possible to collect in all portfolio studies the same basic data on perceived health and activity limitations that are collected in the National Health Interview Survey (NHIS), an ongoing survey of the health of the general population in the United States. That is, the same basic set of core data could be collected in population monitoring, health services research, and clinical and biomedical investigations.
With this design approach, information on perceived health and activity limitation as well as their combined measure, the Health and Activity Limitation Index, collected in smaller and focused clinical study groups, would be directly comparable with that collected on representative samples of the U.S. population. With Gulf War veterans as the clinical study population, such comparisons allow examination of the veterans' health status relative to that of their sociodemographic peers in the general population. Similarly, data on the health of veterans participating in the clinical investigations could be linked to findings from epidemiologic or health services studies, if the same core health status measures are used in each.
Linking the portfolio of studies to an ongoing national survey such as the NHIS through a core of common measures provides a basis for distinguishing changes in health-related quality of life that are due to changes in health care from those changes that are due to other factors, such as economic conditions experienced by veterans since the War, versus participation in the War. For example, analysis of the Health and Activity Limitation Index over the 1984–1994 interval indicated that the decline in population health was in part due to the economic recession that occurred in the early 1990s (Erickson, in press).
Other Information Beyond the Core
The white space in the horizontal bars of Figure 4-1 illustrates that studies will include information other than that in the core set of measures. The types of data collected will vary according to the purpose of the various investigations, as represented by the horizontal axis. For example, health data collected in population studies are less likely to consist of physiological measures, such as blood pressure readings, than are data collected for use in clinical or biomedical investigations. Similarly, health services research studies are likely to focus more on use of health care services or costs (e.g., drawing on elements of the Medical Expenditure Panel Survey) than will either population studies or clinical investigations.
To guide and coordinate studies of the health of Gulf War veterans, the committee proposes a research portfolio that will encompass population studies, health services research studies, and clinical and biomedical investigations.
Within this portfolio, high priority should be assigned to conducting a prospective cohort study that can detect differences in health status among specific populations (e.g., Gulf War veterans and nondeployed veterans) and measure changes in health over time. This approach provides the basis for assessing the extent to which Gulf War veterans are experiencing poorer health compared to other relevant veteran and nonveteran populations.
The following chapter describes the proposed design for this prospective cohort study. It also discusses in more detail statistical and other factors that need to be taken into account in mounting such a study.