Why We Need a New Measure of Health
Until the early 1970s, the health of groups of people was measured largely in terms of mortality (e.g., how many people died? at what ages did they die?) and morbidity (e.g., how many people got sick? How many symptoms did they have?). Since then, an important measure of health has been added that looks at how healthy people report that they are, and how well they feel. This is called health related quality of life (HRQOL), or health status.
Health status measures are good predictors of how long people will live and are used in several ways:
- Looking at whether subgroups of people experience poorer health than other groups (health disparities);
- Determining whether an intervention or treatment leads to better health (health outcomes).
- Measures of HRQOL have become very popular, with literally thousands of measures developed over the past several decades for use in research with specific or general groups.
When measures of health status were initially developed, health and the ability to perform various tasks were thought of as meaning the same thing. For example, a person with chronic breathing problems like emphysema is not able to walk very far or climb many stairs. So a quick and reliable measure of their emphysema and their health became how far they could walk, or whether they could climb a flight of stairs.
Questions that asked about these functional abilities became a popular part of health status measures. Function was thought to reflect health, and health was regarded as the same thing as function. This reflected a general view that being disabled meant being sick. This view, that health is the same as function, is still present in some definitions of health (1). Function is still used to measure health, and population data sets often combine chronic health conditions and disability (2).This view, that disability equates to poor health, also underlies some important health economics indicators such as the Disability Adjusted Life Years (DALY's), where disability is placed next to death on a continuum from health to death
A New View of Disability and Health
About 20 years ago, disability researchers and advocates introduced the idea of improving the health of people who already had disabilities. This meant that persons could be thought of as being disabled but also as being healthy. Fairly quickly, some disability researchers began to regard function (the ability to do some things) as separate and distinct from health (a sense of well being).
A person with a disability could also be an athlete, or live a long life, or enjoy a good quality of life (3). A person with a spinal cord injury, a hearing loss, or an intellectual disability could be physically, socially and mentally healthy. This newer way of thinking about health and disability has been endorsed by the World Health Organization in its International Classification of Function, Disability and Health (ICF) (4). The ICF also emphasizes that our environments can increase or decrease how disabled we are.
Problems in Health Measurement Research
Measures of health have not kept up with this newer way of thinking about disability and health. Andresen and Meyers (5) reviewed the 8 most popular measures of health status in terms of their use with persons with disabilities (including the Nottingham Health Profile, WHO QOL, SF-36, the Sickness Impact Profile 68, and the Quality of Well-Being Scale). They concluded that none of the measures are free of biases for people with disabilities, and that we need to understand and address these measurement shortcomings.
The most widely used measure of health status in the US is the Medical Outcomes Study Short Form 36, often called the SF-36. It was initially developed in the 1970s with recent updates. It includes 8 areas or domains of health. One of those domains is a scale of Physical Function. Sample questions from that scale include:
- Does your health now limit you in these activities? If so, how much?
Walking more than a mile
Climbing several flights of stairs
Lifting or carrying groceries
Clearly, a person who uses a wheelchair because of a spinal cord injury (SCI) or cerebral palsy, would have to answer “no” to many of these questions, and as a result would get a lower health status score. People with serious and permanent mobility impairments will always score lower on this measure. The measure is also less likely to show effects of a health promotion program. If you start practicing a healthy lifestyle, and improve how you feel, increase your energy level, and reduce your pain, you will still have to answer “no” to those Physical Function questions. There are other questions on the SF-36 that are not as obvious but are also biased.
Research participants with disabilities find it confusing to report on their health when questions about function are included. Should participants consider their SCI when rating their health or not? Should they answer in terms of using or not using their chair? This problem was illustrated in a study of the Spinal Cord Injury Model Systems Program, a network of research centers on SCI in the US (6). Researchers used the SF-12 (a shorter form of the SF-36) as a measure of health for people with SCI. They told respondents to interpret health as “whatever it means to you,” and then looked to see how people interpreted it. They found that 21% of respondents never considered their SCI in answering, 28% did sometimes, and 51% always interpreted health as including their SCI. The fact that people differ in how they approach answering these questions becomes a real problem for measurement.
One strategy to address this is to rephrase problem items by replacing words such as “walk” with “go”, or to replace them with other questions. This method has been used in several studies (7-9). Unfortunately, this strategy makes it hard for the researcher to compare their findings with studies where the instrument was used in the usual way. More fundamentally, however, there is still the problem that the measure confounds function with health. In a study we just completed (10), we looked at how questions about physical function relate to measures of health in persons with SCI. We determined that they did not help us understand self-reported health at all. In summary, there are a many problems with using a biased instrument for measuring health in persons with disabilities, and few advantages.
MethodsTo address this issue, a National Expert Panel on Health Measurement was assembled to provide guidance to the overall process of developing a “function-free” measure of health. This panel includes:
- Elena Andresen—University of Florida at Gainesville
- Vincent Campbell—Centers for Disease Control and Prevention
- Brad Cardinal—Oregon State University
- Charles Drum—Oregon Health & Science University
- Glenn Fujiura—University of Illinois, Chicago
- Trevor Hall—Oregon Health & Science University
- Willi Horner-Johnson— Oregon Health & Science University
- Gloria Krahn—Oregon Health & Science University
- Peg Nosek—Baylor College of Medicine
- Jana Peterson— Oregon Health & Science University
- Rie Suzuki—Oregon Health & Science University
A series of studies have been conducted under the guidance of this panel. These studies will be reported on by other members of the panel.
First, we reviewed existing measures of health related quality of life from the perspective of functional bias in the measures. Dr. Trevor Hall will report on that work.
Second, we looked at a measure of health status that is used in population surveys such as the Behavior Risk Factor Surveillance System. This is a series of 9 questions that appear promising for being “function-free”, but we are not certain what components of health those questions address, and whether those questions are understood the same by people with and without disabilities. Drs. Willi Horner-Johnson and Elena Andresen will report on the findings of those studies.
Next, we will hear from Dr. Peg Nosek who has examined previous studies to see whether there are gender effects in health status—do men and women respond to these measures differently.
And finally, I will return to describe the steps we have taken in developing and testing a new function-free measure of health status.
Dr. Gale Roid, a consultant on measurement development, will provide some of his thoughts and impressions, followed by a Question and Answer session.
- Last, J.M., (2001). A Dictionary of Epidemiology, Fourth Edition. New York, NY: Oxford University Press.
- Cott, CA, Gignac, MAM., & Badley , EM. Determinants of self rated health for Canadians with chronic disease and disability. Journal of Epidemiology and Community Health 1999; 53:731–736.
- Albrecht GL, Devlieger PJ. The disability paradox: high quality of life against all odds. Social Science and Medicine 1999;48:977-88.
- World Health Organization, (2001). International Classification of Functioning, Disability and Health Geneva, Switzerland: World Health Organization.
- Andresen EM, Meyers AR. Health-related quality of life outcomes measure. Archives of Physical Medicine and Rehabilitation 2000;81:S30-S45.
- Tate DG, Kalpakjian CZ, Forchheimer MB. Quality of life issues in individuals with spinal cord injury. Archives of Physical Medicine & Rehabilitation, 2002; 83:S18-25.
- Froelich-Grobe K, Andresen EM, Caburnay C, Roberts J, White G. Measuring health-related quality of life for persons with physical disabilities: An enabled version of the Short-form 36 (SF-36E). Quality of Life Research 2008;17:751-770.
- Dudley-Javoroski S, Shields RK. Assessment of physical function and secondary complications after complete spinal cord injury. Disability & Rehabilitation, 2006; 28: 103-10
- Luther SL, Kromrey J, Powell-Cope G, et al. A pilot study to modify the SF-36V physical functioning scale for use with veterans with spinal cord injury. Archives of Physical Medicine & Rehabilitation, 2006; 87:1059-66.
- Krahn, G.L., Suzuki, R. & Horner-Johnson, W. (in preparation). Modeling self-reported health of persons with spinal cord injury.