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How Many People with a Disability Are There in the World?

  • University of Perugia. Italy
146 Computer Systems Experiences of Users with and without Disabilities
The question of how many people are there in the world with a disability is a
difcult one to answer. Although several global surveys and national population
censuses have provided reliable estimates about the demographic prevalence of
people with disability, the data nevertheless do not coincide with one another,
leaving a broad range of variance to be reconciled. Estimates vary even within
a given sample population. The Irish population census of 2006, for instance,
found that 9.3% of the population (393,785 individuals) reported the presence
of a disability. Later in 2006, the Irish Central Statistics Ofce’s National
Disability Survey (NDS), using a broader denition of disability, identied
an additional 8.1% of the population as “false negatives”—people with a dis-
ability which had gone undeclared—thereby increasing the number of disabled
individuals in Ireland to 18.5% of the population (749,100 individuals) (Central
Statistics Ofce, 2008). Even when a comparison is drawn with other European
countries that share the same or a similar health care system, the answer to our
question remains elusive. In 2005, an Italian sample survey found that 4.7% of
the Italian population (about 2,600,000 individuals) have declared to have some
form of disability (ISTAT, 2007). This gure has actually declined as compared
to the gure recorded in previous years. According to the Italian sample sur-
vey, persons with disabilities are dened as those individuals who, excluding
conditions related to temporary limitations, have said they are not capable of
performing typical activities of daily life, even taking into account the possible
use of medical devices such as prostheses, walking sticks, glasses, etc.
The need for reliable estimates of the global prevalence of disability has
led the World Health Organization (WHO) and the World Bank, working
jointly, to produce the rst ever World Report on Disability (2011). The report
was based on two primary data sources: the WHO World Health Survey of
2002–2004 (Üstün et al., 2003b; WHO, 2002–2004), which includes data from
59countries, and the WHO Global Burden of Disease study, updated in 2004
(WHO, 2008). The rst comprises the largest multinational health and dis-
ability survey ever to use a single set of questions and consistent methods to
collect comparable health data from across multiple countries; the second is
an overall assessment of the health of the world’s population which provides
exhaustive estimates of premature mortality, disability, and loss of health from
different diseases, injuries, and risk factors, drawing on available WHO data
sources and on information provided by Member States. The World Health
Survey and Global Burden of Disease study, however, as they are “based on
very different measurement approaches and assumptions, give global preva-
lence estimates among the adult population of 15.6% and 19.4% respectively”
(WHO and World Bank, 2011, p. 29).
147Why Understanding Disabled Users’ Experience Matters
There are three main reasons that contribute to the difculties in accurately
measuring the prevalence of disabilities through censuses and that combine
to render the data ambiguous and nonunique. These are (1) the universality of
disability, (2) the denitional paradox of disability, and (3) the contextual fac-
tors affecting the self-perception of disability.
The universality o f disability. Since the 1980s, star ting with Irving Zola’s (1989,
1993) universal model of disability and continuing through to the biopsychosocial
model of disability adopted by the WHO as a universal framework for classify-
ing (2001) and for collecting disability data (WHO and World Bank,2011), dis-
ability has come to be dened not as something which is to be experienced only
by minority groups—due to bias, prejudice, segregation, or discrimination—as
a xed and dichotomous entity that “demarks one portion of humanity from
another (as gender does, and race sometimes does)” (Bickenbach et al., 1999,
p. 1182). Only in a purely theoretical construct, one might nd in an individual
either a full disability or a full ability. Disability is instead properly understood
as a uid and continuous experience that any human being has to tackle over the
course of their life: “it is an innitely various but universal feature of the human
condition” (Bickenbach et al., 1999, p. 1182). Disability is a type of individual’s
functioning in which the term “impairment” is not adequately descriptive.
Disability is not a set of immutable characteristics that dene a person over
another nor is it predictable by a medical diagnosis since it is not a direct con-
sequence of disease, but it is, instead, a multidimensional process that lasts a
lifetime and involves the physical, psychic, and social spheres of the individual.
(Federici et al., 2012a, pp. 27–28)
Given this broad meaning of disability (universality) and its strict relation to
human functioning (the biopsychosocial model), any classication of an indi-
vidual as having a disability is a question of a threshold of severity that any
survey might arbitrarily state. The universality of disability is therefore the
rst reason that makes it difcult in measuring disability.
The denitional paradox. A major problem encountered by experts in dis-
ability measurement is closely related to the complex denition of disabil-
ity (Üstün et al., 2003a). In the International Classication of Functioning,
Disability and Health (ICF), in fact, disability arises out of activity limita-
tions and participation restrictions, which are determined by the interaction
between the functioning of body functions and structures and the conditions
set by the contextual factors (see also Box 3.1)
Since only one or two of these dimensions of disability are reected in measures
in any given survey […], the data will only capture a portion of the popula-
tion, those who exhibit the specic aspects of disability the questions represent.
(Altman and Gulley, 2009, p. 544)
The “denitional paradox” (Madans and Altman, 2006) surrounding disability
is derived from the operational nature of the disability concept, according to
148 Computer Systems Experiences of Users with and without Disabilities
which any theoretical denition implies aporia while any operational mean-
ing is determined by the purpose of research. Madans and Altman have stated
that “there is no single operational denition of disability (multiple sets of
questions, linked to the different purposes of measurement, may be needed),
and consequently, that “different operational denitions lead to different esti-
mates” (2006). In a complex model such as this,
each domain represents a different area of measurement and each category
or element of classication within each domain represents a different area of
operationalization of the broader domain concept. To generate a meaningful
general prevalence measure one must determine which component best reects
the information needed to address the purpose of the data collection. (Mont,
2007, p. 4)
Put simply, the selection of the purpose motivating the data collection deter-
mines which denition is to be used. Since disability is a complex, mul-
tidimensional experience, the numbers of people with disability and their
circumstances (paradoxically) vary both across (e.g., between the World
Health Survey and the Global Burden of Disease study) and within countries
(e.g., the earlier instance of the Irish population census as compared to the
NDS) inuenced by these different approaches to the measuring of disability.
The contextual factors. People with the same impairment can perceive very
different types and degrees of social participation restrictions and activity
limitations depending on context (WHO and World Bank, 2011). According
to the ICF
contextual factors represent the complete background of an individual’s life
and living. They include two components: Environmental Factors and Personal
Factors— which may have an impact on the individual with a health condition
and that individual’s health and health-related states. (WHO, 2001, p. 22)
Two women, one of whom lives in Stockholm and the other in Kabul, both of
whom lost the use of their legs due to a spinal cord injury and are thus reliant
on a wheelchair for mobility, would experience their individual functioning
and disability in very different ways. The condition of the streets, the avail-
ability and accessibility of public transportation, the housing spaces available,
and the sociocultural status of and the attitudes toward women would all con-
spire to make each woman’s actions in her current environment drastically
different from one another, even though both have the same individual abilities
to execute the same actions. In addition to these socioenvironmental factors,
which make it so difcult to census disability around the world, one must con-
sider personal factors such as those relating to perceptions of the morbidity
of a disease, as well. As the Nobel Prize-winning economist Amartya Sen
has stated (1998, 2002), there is a conceptual contrast between health percep-
tion versus observation. Tension often exists between internal or subjective
views of health and health-related conditions, based on the individual’s own
149Why Understanding Disabled Users’ Experience Matters
2. It approaches accessibility as a world apart, an optional feature of the inter-
face, instead of a main component of the interaction. In light of this, the
access is something that pertains to the technology, without any link to the
UX of the interaction.
As we have already discussed in Chapter 2, and underlined in Chapters 4 and 5, the
assessment of accessibility does not consist in a test for granting access to people
with special needs, but rather it is a necessary step of any kind of interaction evalu-
ation for improving the intrasystemic dialogue between a psychotechnology and any
typology of user. Moreover, disabled users, as well as users without disabilities, must
be involved by evaluators in an overall assessment of the interaction (i.e., measuring
accessibility, usability, and UX).
Therefore, the assessment of accessibility cannot be reduced to an analysis of
conformance to the rules, because it is part of a multistep process in which acces-
sibility, usability, and UX are measured by different techniques involving experts’
and mixed users’ samples (i.e., with and without disability).
The main advantage of this multistep process is that the overall interaction data
collected in the assessment, by the evaluator, can be discussed with the designers
for concurrently deciding how to modify the product’s features and how to opti-
mize the intrasystemic dialogue, in line with the real needs and expectations ana-
lyzed by a mixed sample of users. In particular, the involvement of the disabled
users in the evaluation cohort, by extending the population of interaction behaviors
perceptions, and external or objective views of that same individual’s health
status based on the observations of doctors or professionals. In Sen’s research
into differences in the self-perception of own pathological conditions (also
understood as morbidity; Sen, 1998, 2002), North Americans were found to
have a morbidity score 10 times higher than that perceived by the people of
Bihar, one of the poorest Indian states. According to these results, we should
infer that the health conditions of the people of Bihar are better than those
of North Americans (Federici and Olivetti Belardinelli, 2006). Therefore, the
contextual factors, the third reason affecting the self-perception of disability,
are considered to have a strong impact in the way that a same health condition
is perceived as disabling.
How many people with a disability are there in the world? Among the adult
population, the gure is estimated between 15.6% and 19.4% of the global
population. Since “global aging has a major inuence on disability trends”
(WHO and World Bank, 2011, p. 34) and “one third [2 billion] of the popula-
tion is forecast to be 60 years and older in 2050” (WHO, 2011, p. vii)—which
would be “more than double the number of children in developed countries”
(UN, 2007, p. 8)—seriously considering the accessibility of products, services,
environments, or facilities is not just a matter of human rights but is an issue of
numbers and marketing, as well.
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