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Standards for validating health measures: Definition and content
J Chron Dis Vol. 40. No. 6, pp. 473480, Printed
in Great
Britain.
1987
All rights reserved
Copyright
0
0021-9681/87 $3.00 + 0.00 1987 Pergamon Journals Ltd
Original Articles STANDARDS
FOR VALIDATING HEALTH DEFINITION AND CONTENT JOHN
The RAND
Corporation,
E.
WARE
MEASURES:
JR*
1700 Main Street, P.O. Box 2138, Santa Monica,
CA 904062138,
U.S.A
Abstract-Adherence to standards for judging the content validity of health measures and for labeling them is needed for the field of health assessment to proceed in an orderly fashion. This paper discusses the dimensionality of health and the range of health states that can be measured within each dimension. These two attributes of published definitions of health are used to derive minimum standards for judging the validity of health measures in terms of their content. Five generic health concepts are defined: physical health, mental health, social functioning, role functioning, and general health perceptions. Items from widely used health measures are presented to clarify distinctions among these concepts and the different health states they encompass. It is recommended that labels be assigned to health measures in a manner consistent with their content and other evidence of validity. Health
index
Health
status
measurement
Validity
of health
scales
definition is the blueprint underlying the construction of health measures. It is the standard against which the content validity of health measures should be judged. With the goal of resolving this issue, a review of various definitions of health is presented and the more important health concepts are identified. These concepts are defined and used to derive minimum standards for judging the content validity of health survey instruments. Empirical standards for validating health measures are not addressed here.
INTRODUCTION DEMAND for information about health is greater now than ever before. As a result, opportunities to gain experience in developing and refining health measures will occur with increasing frequency. These opportunities include general population health surveys, evaluations of health policy options that focus on health benefits, health services research, clinical trials, and clinical practice. Expectations are high and the challenge to the state-of-the-art of health assessment is great. In the face of this opportunity, how likely is it that the field will advance in an orderly fashion? Many factors will determine the answer to this question. Among the issues crucial to the development of the state-of-the-art of health assessment is the degree of correspondence between health concepts and specific operational definitions. What is health? Reconciliation of disagreement about the definition of health is essential because that
THE
WHAT
IS HEALTH
At the risk of oversimplification, let us begin with the simple notion that life has two dimensions: quantity and quality. The distinction betwen them is well illustrated ‘in the common greeting “may you have a long and healthy life.” Length of life is expressed in terms of average life expectancy, mortality rates, deaths due to specific causes, and numerous other indicators [I]. In developed countries, these indicators are of little value in understanding the quality of years lived [2]. Thus, measurement of the second dimension of life requires another set of indicators.
*Author for correspondence. Preparation of this paper was supported by grants for the Medical Outcomes Study from the Robert Wood Johnson Foundation, The Henry J. Kaiser Family Foundation, and The Pew Memorial Trust. 473
414
JOHN E. WARE JR
It has become fashionable to equate health, defined comprehensively, with quality of life [3-61. However, it is important to keep in mind that quality of life, as traditionally defined, is a much broader concept than health [7]. In addition to health, quality of life encompasses standard of living, the quality of housing and the neighborhood in which one lives, job satisfaction, and many other factors. A review of the content of survey instruments widely used in quality of life studies during the past decade underscores the importance of this distinction [g, 91. The popularity of the quality of life concept in the health care literature is understandable, given the increasing comprehensiveness of health measures. While health used to be defined primarily in terms of death and the extent of morbidity (i.e. disease), the emerging conceptualization of health is far broader [7, lo]. It encompasses how well people function in everyday life and personal evaluations of well-being. To distinguish the new conceptualization from the old, the term “quality of life” has been adopted. This practice has some utility. It provides a shorthand for making reference to a collection of qualitative concepts, and it has facilitated the recognition and understanding of these concepts in the literature on clinical trials and clinical practice [5,6] Ultimately this use of the quality of life nomenclature is likely to cause some confusion because it is too encompassing. Jobs, housing, schools, and the neighborhood are not attributes of an individual’s health, and they are well outside the purview of the health care system [7, lo]. There is good reason to favor a more limited definition when measuring the health of an individual. The goal of the health care system is to maximize the health component of quality of life, namely health status. Measures of health outcomes should be defined accordingly. Dimensions of health An important feature of health is its dimensionality. Health has distinct components. To fully understand health at a point in time, as well as changes in health over time, these components must be measured and interpreted separately. What are these components? We find clues in definitions of health offered by the World Health Organization [l l] as well as in dictionaries. The WHO defined health as a “state of complete physical, mental, and social well-being
and not merely the absence of disease or infirmity.” Dictionary definitions also identify both physical and mental dimensions of health. The former pertains to the body and bodily needs, the iatter to the mind are particularly to the emotional and intellectual status of the individual. Health connotes “completeness”nothing is missing from the person; it connotes “proper functions”--all is working efficiently. The dictionary also suggests “well-being”health includes “soundness” and “vitality.” Thus, both the WHO and dictionary definitions provide clear precedents for the dimensionality of health and specifically for the distinction between physical and mental health. Empirical evidence in support of this distinction is also quite convincing [ 10, 121. Two features of these definitions are crucial; namely, the dimensionality of health and the full spectrum of health states ranging from disease to well-being. The distinction among specific dimensions of health is the first criterion recommended for evaluating the content of a health measure. From the definitions discussed above, five distinct dimensions are identified: physical health, mental health, everyday functioning in social and in role activities, and general perceptions of well-being. Recognizing that for some purposes more specific information may be required, measurement of these five dimensions is recommended as a minimum standard for health measures that claim to be comprehensive. The range of measurement Second only in importance to comprehensiveness is the range of health states that must be assessed by a health measure. Many widely used scales artificially restrict the range of individual differences in health they enumerate. Consistent with a disease orientation, most emphasize the negative end of the health continuum. The result is a substantial loss of information. The situation is analogous to a scale for measuring weight that ends at 100 pounds. All objects that weigh more are assigned the same score. This is satisfactory for a world where nothing weighs more than 100 pounds or where differences above 100 pounds are irrelevant. An important development in health assessment during the past decade has been the construction of reliable scales that extend into the wellbeing range. Thus, the second criterion recommended for evaluating the content of a health status measure is the range of measurement it permits.
Content Validity of Health Measures
Scales that restrict the range of measurement, other considerations being equal, are inferior to scales that do not. Differences in health and changes in health over time will be measured more precisely, with corresponding gains in the power of hypothesis-testing, by scales that assess the full range of health states [13]. Two clues for evaluating this important feature are the distributions of scores observed in general and in patient populations, and the content of scale items. Measures that tap the full range of individual differences in health will yield distribution of scores with greater variability; fewer people will obtain a perfect score. A review of content should reveal items that focus on positive health states (e.g. well-being and vitality). REVIEW
OF GENERIC
HEALTH
CONCEPTS
At a minimum, measurement of five health concepts is necessary to achieve the breadth inherent in the definitions of health discussed above. To reiterate, they are: physical health, mental health, social functioning, role functioning, and general well-being. These concepts have important features in common. First, each is generic and, thus, should be universally applied in studies of health regardless of the population of interest. Second, each is distinct both conceptually and in terms of the patterns of empirical results observed when studied in relation to other variables [12]. Therefore, each should be measured and interpreted separately prior to aggregation. Comments about these concepts presented below are based on the author’s experience in trying to measure them and on reviews of the published literature. A thorough review of the rather substantial body of literature that has accumulated about these concepts is beyond the scope of this paper. Observations about the content of published measures and empirical results are discussed elsewhere for physical and role functioning [ 131, general mental health [14], social functioning [15, 161 and perceptions of health in general [17]. In addition to results discussed in these reviews, empirical evidence supporting distinctions among the five concepts includes multivariate analyses of associations among health measures [ 12, 171, and multivariate studies that used measures of general medial services [18] of mental health services [19], and health transitions over 3- and 5-year intervals [20,21]. In all applications, measures of these concepts made unique contributions to
4-B
the predictive models evaluated. Thus, each measure contributes information about health not captured by measures of the other concepts. The five generic health concepts are defined below and some comments about their measurement are offered. Examples of health survey items that appear consistent with the definitions appear in Table 1. Items were selected to represent all five generic health concepts and the full range of health states defined by each concept. The entries in Table 1 are illustrations; items and scales should be selected on the basis of many factors, including the goals of measurement, practical considerations, and the population of interest [7]. Physical health
As illustrated by the first entries in Table 1, physical health is commonly measured in terms of limitations in the performance of or ability to perform self-care activities (e.g. eating, bathing, dressing), mobility, and more strenuous physical activities. Measures in this category are generally more valid if they focus on limitations due to physical health problems as opposed to some other cause. It is important to note that the physical health items in Table 1 vary in terms of range of differences in functioning that are assessed. For example, items that assess self-care (e.g. limitations in eating, dressing, bathing, or using the toilet) assess the negative end of the continuum. These limitations are very important because of their consequences. In studies of the severely ill, an extensive battery of measures focused on self-care limitations may be appropriate [22,23]. As a general rule however, items that measure these limitations should be used sparingly in studies of general populations for whom selfcare limitations are relatively rare [13]. Several entries in Table 1 illustrate items that assess important qualitative features of different physical health states. Others tap individual differences in level of effort, pain, difficulty, or need for assistance in performing physical activities [24,25]. If asked only whether they perform a given set of physical activities, two individuals may give identical responses, although they may differ substantially in responses to more qualitative measures of effort and suffering. Thus, qualitative measures enhance precision. Precision for tests of hypotheses about physical health can also be enhanced by the addition of measures tapping physical well-being, energy level, vitality, satisfaction with physical shape
concepts
Orientation memory, alertness.
Cognitive functioning
Social resources Role Role functioning
Social Interpersonal contacts
Limited in kind or amount of major role activity. Working shorter hours. Health causes problem at work. Unable to work because of health.
Freedom from limitations in performance of usual role activities (e.g. work, housework, school) due to poor health.
people to
Number of close friends, talk with.
Frequency of telephone contacts with close friends or relations during specified period of time. Quantity and quality of social ties, network.
Frequency of visits with friends and relatives.
to time and place, attention span, and
Number of friends visited. Going out less often to visit people. How often on telephone with close friends/relatives, past month.
Control of behavior, thoughts, and feelings during specified period.
Personal evaluation of physical condition.
Confinement to bed due to health problems.
Behavioral/ emotional control
Physical well-being Mental Anxiety/ depression
Days in bed
Physical abilities
Psychological well-being
items
health
Depressed or very unhappy. Bothered by nervousness or nerves. Happy, pleased, satisfied with life. Wake up expecting an interesting day. Feel cheerful, lighthearted. Felt emotionally stable. Lose control of behavior, thoughts, feelings. Laugh or cry suddenly. Feel confused, forget a lot, make more mistakes than usual.
Abbreviated
generic
Feelings of anxiety, nervousness tenseness, depression, moodiness, downheartedness. Frequency and intensity of general positive affect.
items measuring
Needs help with bathing, dressing. In bed, chair, couch, for most of day. Do not walk at all. Able to walk uphill, upstairs. Able to participate in sports, strenuous activities. During past 30 days, number of days health keeps one in bed all day or most of day. Rating of physical shape or condition.
Definition
1. Selected
Limitations in performance of self-care, mobility, and physical activities. Ability to perform everyday activities.
Physical Physical limitations
Concepts
Table
[l]
et al. [28] et al. [28]
[50]
[I]
and Ware [16]
and Ware [l6]
Bergner rf al. [28] Hunt [51] Stewart et al. [24]
NCHS
Donald
Donald
Donald and Ware [I61 Bergner er al. [28]
Bergner Bergner
Veit and Ware [29] Dupuy [26, 271 Veit and Ware [29]
Dupuy [26, 271 Costello and Comrey
Bradburn (3 I] Dupuy [26,27]
Dupuy WI Chambers et al. [49]
NCHS
Katz et al. [22] Kaplan, Bush, and Berry [47] Bergner el al. (281 Hulka and Cassel [48] Stewart et al. [24]
References
Content Validity of Health Measures
471
condition, and ability to perform vigorous activities [ 12,25-271.
or
Mental health
While differences in physical health often manifest themselves in behavioral performance, mental health encompasses feelings that may or may not be revealed by overt behavior. For this reason, the content of general mental health measures includes both behavioral dysfunction and the frequency and intensity of symptoms of psychological distress [ l&27,28]. The most efficient way to tap these behaviors and feelings is to ask people about them directly. The distinction between behavioral selfreports and self-ratings of the intensity and frequency of feeling states is not always great. This point is illustrated by the content of items selected from the Sickness Xmpact Profile (SIP), a measure of behavioral dysfunction [28], and the Mental Health Inventory (MHI), a measure of psychological distress and psychological wellbeing [l&29]. Items from the SIP psychosocial and MHI psychological distress dimensions are compared below to illustrate this point: SIP Act nervous Attempted suicide Talk about future in hopeless way
MHI Feel nervous Thought of taking life Feel there is nothing to look forward to
Not surprisingly, given the similarity in content for some SIP and MHI items, these measures are substantially correlated [30]. A noteworthy feature of general measures of mental health pertains to the second standard for judging content, namely, the range of differences they tap throughout the mental health continuum. An important development in the conceptualization of general mental health is the recognition of psychological wellbeing [31,26, 32, 15, 33,291. Earlier measures [34-361 were insensitive to differences in levels of well-being among those free of psychological distress [29]. Clinically and socially relevant changes in mental health are not always captured by measures of psychological distress. The impact of disease and illness may be to “take the top off” of a person’s life. Life becomes less enjoyable or less interesting; there is less about which to be happy and cheerful. Capturing this effect among those who are otherwise free of psychological distress re-
478
JOHN E. WARE JR
quires items that assess psychological wellbeing. General mental health items such as those in Table 1 may not be appropriate for diagnosing specific mental disorders, although some scales with similar item content have proven useful in screening [33]. Interview schedules designed to standardize the diagnosis of selected mental disorders including the Diagnostic Interview Schedule [37] and the Schedule for Affective Disorders and Schizophrenia [38] are also appropriate for this purpose. The third important mental health concept illustrated in Table 1 is cognitive functioning. This concept includes orientation with respect to time and place and such mental processes as memory, comprehension, abstract reasoning, and problem solving [39,40]. Kane and Kane [23] have reviewed available measures of cognitive functioning. Social functioning As illustrated in Table 1, social functioning includes two distinct concepts [15, 161: social contacts and other activities (e.g. visits with friends and relatives), and social ties or resources (e.g. close friends and relatives that can be relied upon for tangible and intangible support), Social contacts are the more directly observable of the two concepts. Measures of social contacts can be criticized for their failure to assess how social events are personally experienced. Counting social activities is analogous to counting feelings without reference to whether they were good or bad. Personal evaluations are therefore necessary to tap the quality of social contacts, a more relevant concept [16]. Social resources cannot be directly observed. The quality of resources can be judged only by the individual, and that quality is best measured by asking about it directly. Measures of social resources represent personal evaluations of the adequacy of interpersonal relationships, including ties to people who will listen to personal problems and provide tangible support and needed companionship. People who are satisfied with their social resources feel “plugged in” or “connected” with others; they feel cared for, loved and wanted [41]. Role functioning Role functioning refers to the performance of, or capacity to perform, usual role activities; included are formal employment, school work, and housework (see Table 1). Although dis-
cussions of health concepts sometimes interchange them, the concepts of role and social functioning [42,43] are distinct and should be interpreted separately. In most populations, limitations in role performance are due to physical health problems. Extreme psychological impairment also disrupts role performance, although this cause is rare relative to the incidence of role limitations due to poor physical health. Effects of psychological impairment on role performance are not likely to be detected by commonly used role functioning measures which do not explicitly ask about limitations due to personal and emotional problems. Role performance reflects physical health and the demands of usual role activity. Thus, the effect of disease and treatment would be expected to vary more for role functioning than for physical functioning. Role limitations are observed both in the presence and in the absence of physical limitations [13]. Pending further research, it may be best to measure and interpret measures of physical and role limitations separately. Standardized measures that distinguish the two concepts are available for this purpose [13, 281. General health perceptions Self-ratings of health in general are among the most commonly used measures of health [ 171. Almost everyone has been asked to provide a rating of his health as “excellent,” “good,” “fair,” or “poor” [l]. These measures are based on the notion that your health is what you think it is. They are considered ratings because they reflect individual differences in the evaluation of information people have about their health. They are considered measures of general health because they have been linked empirically to the other four health concepts defined above [17]. There are two good reasons to measure general health perceptions with items such as those in the fifth section of Table 1. First, personal evaluations of health experiences are not completely captured by items in the other four sections. For example, reports of behavioral performance do not capture important subjective manifestations of differences in health such as pain, difficulty, level of effort required, or worry and concern about health. Second, because measures of limitations or behavioral dysfunctions are inherently negative, they do not extend measurement into the well-being range. Thus, to satisfy the second criterion of content validity, measures of general health
Content
Validity
perceptions that include self-assessments of health, feelings of well-being, energy level, and vitality are required. SUMMARY
A review of definitions of health has proven useful in identifying two important attributes of health that have implications for the content of health measures. These attributes are recommended as minimal standards for judging the content validity of health measures. Given that health is a multidimensional concept, the first standard requires representation of major health dimensions. Five distinct health concepts or dimensions were identified and defined: physical health, mental health, social functioning, role functioning, and general health perceptions. Given that health is more than the absence of disease and dysfunction, the second standard requires representation of positive states of well-being. Thus, measures of the five health concepts must represent the full range of health levels or states from dysfunction or distress to levels of well-being. The distinction between generic and diseaseor treatment-specific measures is an important one. The minimum set of concepts and specific examples of measures discussed here are important should capture generic, and differences in health in any adult population including those suffering from specific diseases [lo, 441. However, generic measures should not be expected to completely capture the particular effects of disease or treatment. When such effects are hypothesized, generic measures should be supplemented with measures that focus specifically on those effects. Examples of such measures have been published in studies of patients with arthritis [45,46]. The development of health status measures and the accumulation of experience with health concepts will proceed in a more orderly fashion if the content of specific measures is accurately presented in publications of results. Ideally, specific operational definitions should be published or referenced. When results are summarized, confusion can be avoided if labels assigned to health variables are consistent with the content of the measure and other evidence of validity. For example, a scale that assesses only limitations due to poor health should not be labeled a measure of well-being. Minimal standards of content validity such as those recommended here should be satisfied before
of Health
Measures
479
claims are made regarding the comprehensiveness of a health measure. Investigators seem predisposed to label their scales in terms of what they want them to measure rather than in terms of their content and other evidence of validity. Definitions of five generic health concepts and two standards of content validity are offered here with the goal of facilitating effective communication while advancing the field of health assessment. REFERENCES
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NCHS: Health. United States: U.S. Department of Health and Human Services, 1981 Elinson J: Introduction to the theme: Sociomedical health indicators. In .%&o-Medical Health Indicators, Elinson J, Siegmann AE (Eds). Farmingdale, N.Y.: Baywood Publishing Company, Inc., 1979. pp. 3-8 Wenger NK: The concept of Quality of Life. Q Life Cardiovasc Care 1: 8-14, 1984 Wenger NK, Mattson ME, Furberg CD et a[: Assessment of Quality of Life in Clinical Trials of Cardiovascular Therapies. New York: Le. Jacq Publishing Co., 1984 Croog SH, Levine S, Testa MA et nl: The effects of antihypertensive therapy of the quality of life. N Engl J Med 314: 1657-1664, 1986 Chobanina AV: Editorial, Antihypertensive therapy in evolution. N Engl J Med 314: 1701-1702, 1986 Ware JE: Methodological Considerations in the Selection of Health Status Assessment Precedures. In Assessment of Quality of Life in Clinical Trials of Cardiovascular Disease, Wenger NK et nf. (Eds). New York: Le Jacq Publishers, 1984. pp. 87-111 Campbell A, Converse PE, Rodgers WL: The Quality of American Life. New York: Russell Sage Foundation, 1976 Andrews FM, Withey SB: Social Indicators of WellBeing. New York: Plenum Press, 1976 Ware JE Jr: The Assessment of Health Status. In Applications of Social Science to Clinical Medicine and Health Policy, Aiken LH, Mechanic D (Eds). New Brunswick, N.J.: Rutgers University Press, 1986. pp. 204228 World Health Organization: Constitution of the World Health Organization. In Basic Documents. Geneva: WHO, 1948 Ware JE, Davies-Avery A, Brook RH: Conceptualization and Measurement of Health for Adults in the Health Insurance Study, Vol. VI. Analysis of Relationships Among Health Status Measures. Santa Monica, Calif.: The RAND Corporation (R-1987/6HEW), 1980 Stewart AL, Ware JE, Brook RH et al: Conceptualization and Measurement of Physical Health for Adults in the Health Insurance Study, Vol. II. Physical Health in Terms of Functioning. Santa Monica, Calif.: The RAND Corporation (R-1987/2-HEW), 1978 Ware JE, Johnston SA, Davies-Avery A ef al: Conceptualization and Measurement of Health for Adults in the Health Insurance Study, Vol. III. Mental Health. Santa Monica, Calif.: The RAND Corporation (R-1987/3-HEW), 1979 Donald CA, Ware JE, Brook RH et al: Concep tualization and Measurement of Health for Adults in the Health Insurance Study, Vol. IV. Social Health. Santa Monica, Calif.: The RAND Corporation (R-1987/4-HEW), 1978
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CA, Ware JE: The measurement of social 16. Donald support. In Research in Community Mental Health, Greenley JR (Ed.). Greenwich, Connecticut: JAI Press, Inc., 1984. pp. 325-370 17. Davies AR, Ware JE Jr: Measuring Health Perceptions in the Health Insurance Experiment. Santa Monica, Calif: The RAND Corporation (R-2711HHS), 1981 WG Jr, Newhouse JP, Ware JE Jr: The 18. Manning status of health in demand estimation; or beyond excellent, good, fair, poor. In Economic Aspects of Health, Fuchs VR (Ed). Chicago: University of Chicago Press, 1982. pp. 143-184 19. Ware JE, Manning WG, Duan N et al: Health status and the use of outpatient mental health services. Am Psycho1 39: lOSO-ilOO, 1984 20. Brook RH, Ware JE Jr, Rogers WH et al: Effect of Coinsurance on the Health of Adults. Santa Monica, Calif.: The RAND Corporation (R-3055-HHS), 1984 21. Ware JE, Brook RH. Roeers WH et al: Health Outcomes’ for Adults in Prepaid And Fee-for-Service Systems of Care: Results from tbe Health Insurance Exueriment. Santa Monica. Calif.: The RAND Corpoiation (R-3459-HHS), 1; press, 1987 RW et al: Studies of 22. Katz S, Ford AB, Moskowiiz illness in the aeed. JAMA 185: 94-99. 1963 23. Kane RA, Kaie RL: Assessing the ‘Elderly. Lexington, Mass.: Lexington Books, 1981 24. Stewart AL, Ware JE Jr, Brook RH: Advances in the measurement of functional status: Construction of aggregate indexes. Med Care 19: 473488, 1981 AM: Functional capacity evaluation; An 25. Jette Empirical approach. Arch Physical Med Rehabil 61: 85-89, 1980 section of the current 26. Dupuy HJ: The psychological Health and Nutrition Examination Survey. Proc Public Health Conf on Records and Statistics Meeting Jointly with the National Conference on Health Statistics. Washington, D.C.: National Conference on Health Statistics, 1972 HJ: The Psychological General Well-being 27. Dupuy (PGWB) Index. In Assessment of Quality of Life in Clinical Trials of Cardiovascular Therapies, Wenger NK et al. (Eds). New York: Le Jacq Publishing Co., 1984. pp. 170-183 M, Bobbitt RA, Pollard WE et al: The 28. Bergner sickness impact profile: Validation of a health status measure. Med Care 14: 57-67, 1976 29. Veit CT, Ware JE Jr: The structure of psychological distress and well-being in general pdpulations. J Consul Clin Psvchol 51: 73&742, 1983 communication, Department of 30. Hall J: Persohal Community Medicine, Westmead Centre, The Paramatta Hospitals, Westmead, Australia, January, 1986 31. Bradbum NM: The Structure of Psychological WellBeing. Chicago: Aldine Publishing Co, 1969 32. Radloff LS: The CES-D scale: A self-report depression scale for research in the general population. Appl Psycho1 Measurement 3: 385401, 1977 Goldberg D: 1978. Manual of the General Health 33 Questionnaire. Windsor, England: NFER Publishing Co., 1978 Macmillan AM: The Health Opinion Survey: Tech34 nique for estimating prevalence of psychoneurotic and
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JR related types of disorder in communities. Psycho1 Rep 3: 325-339, 1957 Gurin G, Veroff J, Field S: Americans View Their Mental Healt&A Nationwide Interview Survey. New York: Basic Books, 1960 Langner TS: A twenty-two item screening score of psychiatric symptoms indicating impairment. J Health Human Rehav 3: 269-276, 1962 Robins LN, Helzer JE, Cougfian J et al: National Institute of Mental Health Diagnostic Interview Schedule: Its history, characteristics, and validity. Arch Gen Psychiat 38: 381-389, 1981 Endicott J, Spitzer RL: A diagnostic interview: The schedule for affective disorders and schizophrenia. Arch Cen Psychiat 35: 837-844, 1978 Folstein MF, Folstein S., McHugh PR: Mini-mental state: A practical method for grading the cognitive state of patients for the clinician. J Psychiat Res 12: 189-198, 1975 Dohrenwend BP, Levav I, Shrout PE: Screening scales from the Psychiatric Epidemiology Research Interview (PERI). In Communitv Survevs. Mvers JK. Weissman ‘MH (Eds). New Bruhswick,-N.J.:-Rutgers University Press, 1983 Cobb S: Social Support as a Moderator of Life Stress. Psychosom Med 38: 30&314, 1976 Patrick DL, Bush JW, Chen MM: Methods for measuring levels of well-being for a health status index. Health Serv Res 8: 228-245, 1973 Reynolds WJ, Rushing WA, Miles DL: The validation of a functional status index. J Health Sot Rehav 15: 271-288, 1974 Nelson E, Conger B, Douglass R ef al: Functional health status levels of primary care patients. JAMA 249: 3331-3337, 1983 Fries JF, Spitz P, Kraines RG, Holman HR: Measurement of patient outcome in arthritis. Arth Rheum 23: 137-145, 1980 Meenan RF, Anderson JJ, Kazis LE. et al: Outcome assessment in clinical trials. Arth Rheum 27: 13441352, 1984 Kaplan RM, Bush JW, Berry CC: Health status: Types of validity and the index of well-being. Health Serv Res 11: 478-507, 1976 Hulka BS, Cassel JC: The AAFP-UNC study of the organization, utilization and assessment of primary medical care. Am J Public Health 63: 494-561, 1973 Chambers LW. MacDonald LA. Tugwell P et nl: The McMasler He&h Index Quest&n&e as a measure of quality of life for patients with rheumatoid disease. J Rheumatol 9; 780-784, 1982 Costello CG, Comrey AL: Scales for measuring depression and anxiety. J Psycho1 66: 303&3313, 1967 Hunt SM, McEwen J, McKenna SP ef al: The Nottingham Health Profile: Subjective health status and medical consultations. Sot Sci Med 15A: 221-229, 1981 Ware JE Jr: Scales for measuring general health perceptions. Health Serv Res 11: 39-15, 1976 Daut RL, Cleeland CS, Flanery RC: Development of the Wisconsin brief pain questionnaire to assess pain in cancer and other diseases. Pain 17: 197-210, 1983
in Great
Britain.
1987
All rights reserved
Copyright
0
0021-9681/87 $3.00 + 0.00 1987 Pergamon Journals Ltd
Original Articles STANDARDS
FOR VALIDATING HEALTH DEFINITION AND CONTENT JOHN
The RAND
Corporation,
E.
WARE
MEASURES:
JR*
1700 Main Street, P.O. Box 2138, Santa Monica,
CA 904062138,
U.S.A
Abstract-Adherence to standards for judging the content validity of health measures and for labeling them is needed for the field of health assessment to proceed in an orderly fashion. This paper discusses the dimensionality of health and the range of health states that can be measured within each dimension. These two attributes of published definitions of health are used to derive minimum standards for judging the validity of health measures in terms of their content. Five generic health concepts are defined: physical health, mental health, social functioning, role functioning, and general health perceptions. Items from widely used health measures are presented to clarify distinctions among these concepts and the different health states they encompass. It is recommended that labels be assigned to health measures in a manner consistent with their content and other evidence of validity. Health
index
Health
status
measurement
Validity
of health
scales
definition is the blueprint underlying the construction of health measures. It is the standard against which the content validity of health measures should be judged. With the goal of resolving this issue, a review of various definitions of health is presented and the more important health concepts are identified. These concepts are defined and used to derive minimum standards for judging the content validity of health survey instruments. Empirical standards for validating health measures are not addressed here.
INTRODUCTION DEMAND for information about health is greater now than ever before. As a result, opportunities to gain experience in developing and refining health measures will occur with increasing frequency. These opportunities include general population health surveys, evaluations of health policy options that focus on health benefits, health services research, clinical trials, and clinical practice. Expectations are high and the challenge to the state-of-the-art of health assessment is great. In the face of this opportunity, how likely is it that the field will advance in an orderly fashion? Many factors will determine the answer to this question. Among the issues crucial to the development of the state-of-the-art of health assessment is the degree of correspondence between health concepts and specific operational definitions. What is health? Reconciliation of disagreement about the definition of health is essential because that
THE
WHAT
IS HEALTH
At the risk of oversimplification, let us begin with the simple notion that life has two dimensions: quantity and quality. The distinction betwen them is well illustrated ‘in the common greeting “may you have a long and healthy life.” Length of life is expressed in terms of average life expectancy, mortality rates, deaths due to specific causes, and numerous other indicators [I]. In developed countries, these indicators are of little value in understanding the quality of years lived [2]. Thus, measurement of the second dimension of life requires another set of indicators.
*Author for correspondence. Preparation of this paper was supported by grants for the Medical Outcomes Study from the Robert Wood Johnson Foundation, The Henry J. Kaiser Family Foundation, and The Pew Memorial Trust. 473
414
JOHN E. WARE JR
It has become fashionable to equate health, defined comprehensively, with quality of life [3-61. However, it is important to keep in mind that quality of life, as traditionally defined, is a much broader concept than health [7]. In addition to health, quality of life encompasses standard of living, the quality of housing and the neighborhood in which one lives, job satisfaction, and many other factors. A review of the content of survey instruments widely used in quality of life studies during the past decade underscores the importance of this distinction [g, 91. The popularity of the quality of life concept in the health care literature is understandable, given the increasing comprehensiveness of health measures. While health used to be defined primarily in terms of death and the extent of morbidity (i.e. disease), the emerging conceptualization of health is far broader [7, lo]. It encompasses how well people function in everyday life and personal evaluations of well-being. To distinguish the new conceptualization from the old, the term “quality of life” has been adopted. This practice has some utility. It provides a shorthand for making reference to a collection of qualitative concepts, and it has facilitated the recognition and understanding of these concepts in the literature on clinical trials and clinical practice [5,6] Ultimately this use of the quality of life nomenclature is likely to cause some confusion because it is too encompassing. Jobs, housing, schools, and the neighborhood are not attributes of an individual’s health, and they are well outside the purview of the health care system [7, lo]. There is good reason to favor a more limited definition when measuring the health of an individual. The goal of the health care system is to maximize the health component of quality of life, namely health status. Measures of health outcomes should be defined accordingly. Dimensions of health An important feature of health is its dimensionality. Health has distinct components. To fully understand health at a point in time, as well as changes in health over time, these components must be measured and interpreted separately. What are these components? We find clues in definitions of health offered by the World Health Organization [l l] as well as in dictionaries. The WHO defined health as a “state of complete physical, mental, and social well-being
and not merely the absence of disease or infirmity.” Dictionary definitions also identify both physical and mental dimensions of health. The former pertains to the body and bodily needs, the iatter to the mind are particularly to the emotional and intellectual status of the individual. Health connotes “completeness”nothing is missing from the person; it connotes “proper functions”--all is working efficiently. The dictionary also suggests “well-being”health includes “soundness” and “vitality.” Thus, both the WHO and dictionary definitions provide clear precedents for the dimensionality of health and specifically for the distinction between physical and mental health. Empirical evidence in support of this distinction is also quite convincing [ 10, 121. Two features of these definitions are crucial; namely, the dimensionality of health and the full spectrum of health states ranging from disease to well-being. The distinction among specific dimensions of health is the first criterion recommended for evaluating the content of a health measure. From the definitions discussed above, five distinct dimensions are identified: physical health, mental health, everyday functioning in social and in role activities, and general perceptions of well-being. Recognizing that for some purposes more specific information may be required, measurement of these five dimensions is recommended as a minimum standard for health measures that claim to be comprehensive. The range of measurement Second only in importance to comprehensiveness is the range of health states that must be assessed by a health measure. Many widely used scales artificially restrict the range of individual differences in health they enumerate. Consistent with a disease orientation, most emphasize the negative end of the health continuum. The result is a substantial loss of information. The situation is analogous to a scale for measuring weight that ends at 100 pounds. All objects that weigh more are assigned the same score. This is satisfactory for a world where nothing weighs more than 100 pounds or where differences above 100 pounds are irrelevant. An important development in health assessment during the past decade has been the construction of reliable scales that extend into the wellbeing range. Thus, the second criterion recommended for evaluating the content of a health status measure is the range of measurement it permits.
Content Validity of Health Measures
Scales that restrict the range of measurement, other considerations being equal, are inferior to scales that do not. Differences in health and changes in health over time will be measured more precisely, with corresponding gains in the power of hypothesis-testing, by scales that assess the full range of health states [13]. Two clues for evaluating this important feature are the distributions of scores observed in general and in patient populations, and the content of scale items. Measures that tap the full range of individual differences in health will yield distribution of scores with greater variability; fewer people will obtain a perfect score. A review of content should reveal items that focus on positive health states (e.g. well-being and vitality). REVIEW
OF GENERIC
HEALTH
CONCEPTS
At a minimum, measurement of five health concepts is necessary to achieve the breadth inherent in the definitions of health discussed above. To reiterate, they are: physical health, mental health, social functioning, role functioning, and general well-being. These concepts have important features in common. First, each is generic and, thus, should be universally applied in studies of health regardless of the population of interest. Second, each is distinct both conceptually and in terms of the patterns of empirical results observed when studied in relation to other variables [12]. Therefore, each should be measured and interpreted separately prior to aggregation. Comments about these concepts presented below are based on the author’s experience in trying to measure them and on reviews of the published literature. A thorough review of the rather substantial body of literature that has accumulated about these concepts is beyond the scope of this paper. Observations about the content of published measures and empirical results are discussed elsewhere for physical and role functioning [ 131, general mental health [14], social functioning [15, 161 and perceptions of health in general [17]. In addition to results discussed in these reviews, empirical evidence supporting distinctions among the five concepts includes multivariate analyses of associations among health measures [ 12, 171, and multivariate studies that used measures of general medial services [18] of mental health services [19], and health transitions over 3- and 5-year intervals [20,21]. In all applications, measures of these concepts made unique contributions to
4-B
the predictive models evaluated. Thus, each measure contributes information about health not captured by measures of the other concepts. The five generic health concepts are defined below and some comments about their measurement are offered. Examples of health survey items that appear consistent with the definitions appear in Table 1. Items were selected to represent all five generic health concepts and the full range of health states defined by each concept. The entries in Table 1 are illustrations; items and scales should be selected on the basis of many factors, including the goals of measurement, practical considerations, and the population of interest [7]. Physical health
As illustrated by the first entries in Table 1, physical health is commonly measured in terms of limitations in the performance of or ability to perform self-care activities (e.g. eating, bathing, dressing), mobility, and more strenuous physical activities. Measures in this category are generally more valid if they focus on limitations due to physical health problems as opposed to some other cause. It is important to note that the physical health items in Table 1 vary in terms of range of differences in functioning that are assessed. For example, items that assess self-care (e.g. limitations in eating, dressing, bathing, or using the toilet) assess the negative end of the continuum. These limitations are very important because of their consequences. In studies of the severely ill, an extensive battery of measures focused on self-care limitations may be appropriate [22,23]. As a general rule however, items that measure these limitations should be used sparingly in studies of general populations for whom selfcare limitations are relatively rare [13]. Several entries in Table 1 illustrate items that assess important qualitative features of different physical health states. Others tap individual differences in level of effort, pain, difficulty, or need for assistance in performing physical activities [24,25]. If asked only whether they perform a given set of physical activities, two individuals may give identical responses, although they may differ substantially in responses to more qualitative measures of effort and suffering. Thus, qualitative measures enhance precision. Precision for tests of hypotheses about physical health can also be enhanced by the addition of measures tapping physical well-being, energy level, vitality, satisfaction with physical shape
concepts
Orientation memory, alertness.
Cognitive functioning
Social resources Role Role functioning
Social Interpersonal contacts
Limited in kind or amount of major role activity. Working shorter hours. Health causes problem at work. Unable to work because of health.
Freedom from limitations in performance of usual role activities (e.g. work, housework, school) due to poor health.
people to
Number of close friends, talk with.
Frequency of telephone contacts with close friends or relations during specified period of time. Quantity and quality of social ties, network.
Frequency of visits with friends and relatives.
to time and place, attention span, and
Number of friends visited. Going out less often to visit people. How often on telephone with close friends/relatives, past month.
Control of behavior, thoughts, and feelings during specified period.
Personal evaluation of physical condition.
Confinement to bed due to health problems.
Behavioral/ emotional control
Physical well-being Mental Anxiety/ depression
Days in bed
Physical abilities
Psychological well-being
items
health
Depressed or very unhappy. Bothered by nervousness or nerves. Happy, pleased, satisfied with life. Wake up expecting an interesting day. Feel cheerful, lighthearted. Felt emotionally stable. Lose control of behavior, thoughts, feelings. Laugh or cry suddenly. Feel confused, forget a lot, make more mistakes than usual.
Abbreviated
generic
Feelings of anxiety, nervousness tenseness, depression, moodiness, downheartedness. Frequency and intensity of general positive affect.
items measuring
Needs help with bathing, dressing. In bed, chair, couch, for most of day. Do not walk at all. Able to walk uphill, upstairs. Able to participate in sports, strenuous activities. During past 30 days, number of days health keeps one in bed all day or most of day. Rating of physical shape or condition.
Definition
1. Selected
Limitations in performance of self-care, mobility, and physical activities. Ability to perform everyday activities.
Physical Physical limitations
Concepts
Table
[l]
et al. [28] et al. [28]
[50]
[I]
and Ware [16]
and Ware [l6]
Bergner rf al. [28] Hunt [51] Stewart et al. [24]
NCHS
Donald
Donald
Donald and Ware [I61 Bergner er al. [28]
Bergner Bergner
Veit and Ware [29] Dupuy [26, 271 Veit and Ware [29]
Dupuy [26, 271 Costello and Comrey
Bradburn (3 I] Dupuy [26,27]
Dupuy WI Chambers et al. [49]
NCHS
Katz et al. [22] Kaplan, Bush, and Berry [47] Bergner el al. (281 Hulka and Cassel [48] Stewart et al. [24]
References
Content Validity of Health Measures
471
condition, and ability to perform vigorous activities [ 12,25-271.
or
Mental health
While differences in physical health often manifest themselves in behavioral performance, mental health encompasses feelings that may or may not be revealed by overt behavior. For this reason, the content of general mental health measures includes both behavioral dysfunction and the frequency and intensity of symptoms of psychological distress [ l&27,28]. The most efficient way to tap these behaviors and feelings is to ask people about them directly. The distinction between behavioral selfreports and self-ratings of the intensity and frequency of feeling states is not always great. This point is illustrated by the content of items selected from the Sickness Xmpact Profile (SIP), a measure of behavioral dysfunction [28], and the Mental Health Inventory (MHI), a measure of psychological distress and psychological wellbeing [l&29]. Items from the SIP psychosocial and MHI psychological distress dimensions are compared below to illustrate this point: SIP Act nervous Attempted suicide Talk about future in hopeless way
MHI Feel nervous Thought of taking life Feel there is nothing to look forward to
Not surprisingly, given the similarity in content for some SIP and MHI items, these measures are substantially correlated [30]. A noteworthy feature of general measures of mental health pertains to the second standard for judging content, namely, the range of differences they tap throughout the mental health continuum. An important development in the conceptualization of general mental health is the recognition of psychological wellbeing [31,26, 32, 15, 33,291. Earlier measures [34-361 were insensitive to differences in levels of well-being among those free of psychological distress [29]. Clinically and socially relevant changes in mental health are not always captured by measures of psychological distress. The impact of disease and illness may be to “take the top off” of a person’s life. Life becomes less enjoyable or less interesting; there is less about which to be happy and cheerful. Capturing this effect among those who are otherwise free of psychological distress re-
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JOHN E. WARE JR
quires items that assess psychological wellbeing. General mental health items such as those in Table 1 may not be appropriate for diagnosing specific mental disorders, although some scales with similar item content have proven useful in screening [33]. Interview schedules designed to standardize the diagnosis of selected mental disorders including the Diagnostic Interview Schedule [37] and the Schedule for Affective Disorders and Schizophrenia [38] are also appropriate for this purpose. The third important mental health concept illustrated in Table 1 is cognitive functioning. This concept includes orientation with respect to time and place and such mental processes as memory, comprehension, abstract reasoning, and problem solving [39,40]. Kane and Kane [23] have reviewed available measures of cognitive functioning. Social functioning As illustrated in Table 1, social functioning includes two distinct concepts [15, 161: social contacts and other activities (e.g. visits with friends and relatives), and social ties or resources (e.g. close friends and relatives that can be relied upon for tangible and intangible support), Social contacts are the more directly observable of the two concepts. Measures of social contacts can be criticized for their failure to assess how social events are personally experienced. Counting social activities is analogous to counting feelings without reference to whether they were good or bad. Personal evaluations are therefore necessary to tap the quality of social contacts, a more relevant concept [16]. Social resources cannot be directly observed. The quality of resources can be judged only by the individual, and that quality is best measured by asking about it directly. Measures of social resources represent personal evaluations of the adequacy of interpersonal relationships, including ties to people who will listen to personal problems and provide tangible support and needed companionship. People who are satisfied with their social resources feel “plugged in” or “connected” with others; they feel cared for, loved and wanted [41]. Role functioning Role functioning refers to the performance of, or capacity to perform, usual role activities; included are formal employment, school work, and housework (see Table 1). Although dis-
cussions of health concepts sometimes interchange them, the concepts of role and social functioning [42,43] are distinct and should be interpreted separately. In most populations, limitations in role performance are due to physical health problems. Extreme psychological impairment also disrupts role performance, although this cause is rare relative to the incidence of role limitations due to poor physical health. Effects of psychological impairment on role performance are not likely to be detected by commonly used role functioning measures which do not explicitly ask about limitations due to personal and emotional problems. Role performance reflects physical health and the demands of usual role activity. Thus, the effect of disease and treatment would be expected to vary more for role functioning than for physical functioning. Role limitations are observed both in the presence and in the absence of physical limitations [13]. Pending further research, it may be best to measure and interpret measures of physical and role limitations separately. Standardized measures that distinguish the two concepts are available for this purpose [13, 281. General health perceptions Self-ratings of health in general are among the most commonly used measures of health [ 171. Almost everyone has been asked to provide a rating of his health as “excellent,” “good,” “fair,” or “poor” [l]. These measures are based on the notion that your health is what you think it is. They are considered ratings because they reflect individual differences in the evaluation of information people have about their health. They are considered measures of general health because they have been linked empirically to the other four health concepts defined above [17]. There are two good reasons to measure general health perceptions with items such as those in the fifth section of Table 1. First, personal evaluations of health experiences are not completely captured by items in the other four sections. For example, reports of behavioral performance do not capture important subjective manifestations of differences in health such as pain, difficulty, level of effort required, or worry and concern about health. Second, because measures of limitations or behavioral dysfunctions are inherently negative, they do not extend measurement into the well-being range. Thus, to satisfy the second criterion of content validity, measures of general health
Content
Validity
perceptions that include self-assessments of health, feelings of well-being, energy level, and vitality are required. SUMMARY
A review of definitions of health has proven useful in identifying two important attributes of health that have implications for the content of health measures. These attributes are recommended as minimal standards for judging the content validity of health measures. Given that health is a multidimensional concept, the first standard requires representation of major health dimensions. Five distinct health concepts or dimensions were identified and defined: physical health, mental health, social functioning, role functioning, and general health perceptions. Given that health is more than the absence of disease and dysfunction, the second standard requires representation of positive states of well-being. Thus, measures of the five health concepts must represent the full range of health levels or states from dysfunction or distress to levels of well-being. The distinction between generic and diseaseor treatment-specific measures is an important one. The minimum set of concepts and specific examples of measures discussed here are important should capture generic, and differences in health in any adult population including those suffering from specific diseases [lo, 441. However, generic measures should not be expected to completely capture the particular effects of disease or treatment. When such effects are hypothesized, generic measures should be supplemented with measures that focus specifically on those effects. Examples of such measures have been published in studies of patients with arthritis [45,46]. The development of health status measures and the accumulation of experience with health concepts will proceed in a more orderly fashion if the content of specific measures is accurately presented in publications of results. Ideally, specific operational definitions should be published or referenced. When results are summarized, confusion can be avoided if labels assigned to health variables are consistent with the content of the measure and other evidence of validity. For example, a scale that assesses only limitations due to poor health should not be labeled a measure of well-being. Minimal standards of content validity such as those recommended here should be satisfied before
of Health
Measures
479
claims are made regarding the comprehensiveness of a health measure. Investigators seem predisposed to label their scales in terms of what they want them to measure rather than in terms of their content and other evidence of validity. Definitions of five generic health concepts and two standards of content validity are offered here with the goal of facilitating effective communication while advancing the field of health assessment. REFERENCES
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