Suzanne McDermott, PhD, Professor,
University of South Carolina School of Medicine, Department of Family and
Preventive Medicine, Columbia SC 29208
Disability is a human characteristic that
has many dimensions. These dimensions
include medical, functional, civil rights/legal, and social perspectives. The inclination for most scholars and public
health professionals is to pick one of these perspectives and use it
exclusively in program development and research.
The medical model of disability
conceptualizes disability from an impairment standpoint and has been strongly
associated with measurement of deficits and counting of specific problems. The
model has relied on identification of medical diagnoses and/or ICD9 or ICD10
codes from medical records. Another medical model approach used in large
population based studies is to ask individuals to endorse having a disability,
often presented or read from a long list of medical diagnoses and conditions.
In studies such as NHANES and NHIS self report, or family member report, of a
disability is followed by a verification of the diagnosis in medical records.
In other studies, such as the recently released CDC study of autism, the
prevalence is estimated from parental report of having a child with an autism
spectrum disorder diagnosis. The medical literature relies on the counting of
diagnoses and codes to calculate incidence, prevalence, and to report on specific
impairments and conditions. Although the use of data collected in the framework
of the medical model is prominent in the medical and epidemiologic literature
today, the disability community has an uncomfortable response to this model of
disability identification. On the one hand many disability specific groups need
these numbers to support their political action. On the other hand advocates often feel the
medical model is negative and dispassionate.
By and large this model has been discounted by proponents of the
functional limitations and the social models, and they view it as passé.
the past decade the dominant dimension used for the classification of
disability has been the functional model. Using criteria that ask about
limitations in function and use of assistive devices can exclude some people
who have made adaptations or do not acknowledge differences in their functional
ability. Individuals with mental retardation and other cognitive differences
rarely acknowledge limitations in function and are usually missed in prevalence
counts of disability. And on the other
hand, the inclusion of people with functional limitations in the definition of
disability can over representing the magnitude of disability in the US. The latest report from the Dana and Christopher
Reeve foundation found that 1 in 50 Americans (1.9%) has paralysis, defined by the study as a
central nervous system disorder resulting in difficulty or inability to move
the upper or lower extremities.
According to this definition a person with a bracial plexis injury has
paralysis. Does this broad definition fit
with the reality of the general perception of paralysis? Likewise, the
Behavioral Risk Factor Surveillance System uses a two-question screener for
disability (Are you limited in
any way in any activities because of physical, mental, or emotional problems?
Or Do you now have any health problem that requires you to use special equipment,
such as a cane, a wheelchair, a special bed, or a special telephone?).
This definition very likely captures people with obesity, advanced age, and
chronic illness (such as COPD, asthma, diabetes, CHF). Some of these people do
not have an impairment that results in disability. And again, people with a cognitive impairment
almost always respond negatively to both BRFSS questions. As a consequence estimates of obesity and
chronic conditions (diabetes, etc.) among people with disabilities, can be
overestimated using a cross sectional dataset, when the condition might be
causing the disability response.
The social model of disability focuses on
environmental, economic, and political barriers to inclusion since the
underlying belief is that disability is a social construct. The definition of
environment used by proponents of the social model, include physical, social,
economic, and political dimensions. Thus, the usual unit of measurement for
proponents of the social model is the barriers in the environment, and only
secondarily the individuals who are denied participation. This perspective is useful to monitor
compliance with the ADA and to measure and compare communities. It only allows
us to study individuals from a limited perspective.
There have been attempts to provide an
integrated model of disability in the literature. The Nagi Model of the disabling process has
been widely used. And the International Classification of Functioning,
Disability and Health (ICF) received the endorsement of the international
community through the WHO. The ICF model
is a complex classification that can provide a rich description of an
individual. However although this system
of classification recognizes the interaction between the individual and the
environment, and includes many factors, it does not meet the criteria of parsimony
that is a core element of epidemiologic analyses.
The CDC and a number of other organizations
endorsed the use of a two question screener to identify people with
disabilities, so comparisons could be made about prevalence between states and
to identify disparities in term so of health status and service utilization.
These questions were crafted from the functional view of disability. The BRFSS
is the national system that has become the cornerstone for these questions and
the resultant multivariable analyses that have been used to explain health
disparities for people with disabilities. It is time to step back and question
whether this is the best we can do. Can
we really accept the notion that a Chartbook on disability which shows
photographs of a person using a wheelchair contains information that attributes
higher rates of obesity to people with disabilities or should we ask if people
with obesity are responding affirmatively to one of the disability questions
and distorting our notion of cause and effect.
This paper is intended to endorse a
multi-dimensional approach that is parsimonious and useful for
epidemiology. The challenge is to
identify a small set of questions that identify social, function, and medical
issues that constitute a disability case definition. We need to be able to
count people with disabilities to quantify service and support needs and to
study the life course of people with specific disabilities. In addition, it is
important to have more precise measures of disability so comparisons can be
made to identify disparities and to measure changes over time. We need to be careful so there isn’t
confusion about cause and effect (attributing secondary conditions as outcomes
of disability when they are in fact the cause of the functional limitation) and
comparisons to people without disabilities are fair. If we include people who experience
disability due to obesity in the case definition of disability then we cannot
say people with disability are more likely to be obese. The creditability of disability epidemiology
and the disability field is at stake.
few questions, taken together, might improve the sensitivity and specificity of
our case definition.
- Do you use disability related
equipment, such as a wheelchair, walker, TDD, augmentative device?
- Do you identify with or have you
received special services as a member of a disability group?
- If yes to either question, what
is your disability?
we asked these questions instead of the two BRFSS functional limitation core
questions, would it be legitimate to exclude people who identified as very old,
frail due to a progressive disease, or obese, from our definition of
Suzanne McDermott is a Professor and Research Director in the University of
South Carolina, School of Medicine, Department of Family and Preventive
Medicine, where she has been on the faculty since 1988. Dr. McDermott conducts research related to
causes of disability in children and the lives of people with disability. She currently has over $2 million in active
grant support from the NIH, CDC, and HRSA, and over 70 journal articles, and a
book about disability and health for adults with developmental disabilities.
Dr. McDermott teaches medical students and residents, works with state agencies
to evaluate public health and disability programs, and has a daughter with