how many people have communication disorders and why does it matter?
TRANSCRIPT
How many people have communication disorders and why does itmatter?
P. ENDERBY1 & C. PICKSTONE2
1Institute of General Practice and Primary Care, University of Sheffield, and 2Northern General Hospital, UK
AbstractIn this invited paper, Enderby and Pickstone discuss the value of epidemiological research to the field of speech-languagepathology in both child and adult populations. They suggest that epidemiological research informs the development ofmodels of service delivery appropriate to population needs. They also argue for the importance of epidemiologicalinformation in contributing to the determination of ‘‘unmet’’ need for speech-language pathology services.
Introduction
New trends in health care including a shift towards
preventive approaches may extend the role of speech
and language therapists (SLTs) and require them to
understand fundamental principles of epidemiology
(Lubker, 1997). Epidemiology is commonly defined
as the study of the distribution of disease or
physiological condition in human populations and
includes the study of factors that influence this
distribution. Last (1983) broadened this definition to
include ‘‘the study of the distribution and determi-
nants of health-related states or events in specified
populations, and the application of this study to the
control of health problems’’. The field has expanded
still further to take account of factors or risks that
influence patterns of health and disease including
inequalities, neighbourhoods, community, work and
family (Berkman & Kawachi, 2000). This expanded
perspective reflects an understanding that health and
disease are influenced both at the level of the
individual and at the level of the population (Berk-
man & Kawachi, 2000). An understanding of some
of the principles of epidemiology should allow us,
firstly, to determine how much of a disease or health
problem there is within a population. The second
purpose of epidemiology allows us to identify risk
factors for diseases although these may only go part
of the way to explaining ‘‘cases’’. Often risk factors
may be linked to many disease outcomes and not
simply to one. The distinction between genetic and
environmental risk is becoming more clouded.
Finally, models of single risks and outcomes are
being superseded by an understanding of multiple
risks interacting to produce an outcome in the
context of the resilience of the individual and family.
Through studying risk, it may be possible to begin to
elucidate causal pathways and thus, potentially
treatable or even preventable factors. Increasing our
knowledge of the epidemiology of communication
and swallowing disorders should be central to
understanding the natural history of speech and
language impairment and disability as well as to
speech and language therapy research and to the
management and audit of its services. Studies that
concern themselves with the identification of risk
factors may clarify the aetiology of specific conditions
influencing theories for treatment. Epidemiological
methods may also guide the evaluation of prevention
or therapeutic interventions in our populations, or
assist us with targeting interventions if particular
clusters of risk can be identified. Additionally,
increased knowledge of this area will provide some
tools to address questions of whether we are truly
meeting the needs of the population or missing large
groups of persons who may benefit. It is probable
that attrition or coverage results from inadequate
referral routes, poor information or lack of resources.
The place of population studies in clinical
management
Population studies of language or speech are few in
number (Tomblin et al., 1997; Johnson et al., 1999),
Correspondence: P. Enderby, Institute of General Practice and Primary Care, University of Sheffield, Sheffield, UK. Tel: 0114 2715897.
E-mail: [email protected]
Advances in Speech–Language Pathology, March 2005; 7(1): 8 – 13
ISSN 1441-7049 print/ISSN 1742-9528 online # The Speech Pathology Association of Australia Limited
Published by Taylor & Francis Group Ltd
DOI: 10.1080/14417040500055086
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tend to be costly and present particular problems in
terms of follow up and controls although they
provide valuable insights into the natural history of
language difficulties. The measurement of overall
health at a population level where data is aggregated
from individuals should be simpler to devise than
individual indicators, as the degree of error asso-
ciated with generalising from larger distributions is
less than that associated with the prediction of a
particular observation. For example, age may be an
unreliable predictor of performance or health in an
individual (Townsend, 1962) but at the population
level it can be quite a sensitive discriminator. This is
particularly so in communication where the devel-
opment of language for children can be described for
a population year by year and mapped out in a
development sequence with ‘‘milestones’’ or
‘‘stages’’. Even within such a framework, it can be
difficult to discriminate between normal and abnor-
mal progression in an individual child because of the
degree of variance at any single age point. In this
way, defining which children are ‘‘cases’’ is highly
problematic. Clarity about ‘‘cases’’ is fundamental to
a calculation of prevalence which is in turn key to
service planning based on population need. How-
ever, conversely there are some who would argue that
the measurement of health is more complex at the
population level than for an individual. This is not
only because it is too difficult to reliably ascertain
certain sensitive issues of health status in large
groups where symptomology might vary (e.g., the
fluency in stammerers) but also reflects differing
dynamics of health at the population, sub-population
and individual level. Thus, some interventions may
have more profound effect in some individuals in
some populations than overall in that population.
Thus the population studies may mask particular
factors of importance to the delivery of services.
Given this caution, it is still valuable to managers
of speech and language therapy services to have a
broad handle on general epidemiological informa-
tion. The major demographic determinants of a
population’s size and age structure are fertility,
mortality and migration. In most of the developed
world there has been substantial increase in fertility
and in the number of children surviving to maturity.
The numbers of children in the population, along
with their socio-economic standing will provide
some indication of the numbers of children requiring
particular health related services. It may also provide
some clues as to the models of delivery which might
best meet local needs. Additionally, the numbers of
older people, e.g., over 70 years of age surviving in a
particular population should allow managers to
consider the different requirements for different
services (e.g., stroke services). For the first time in
the United Kingdom the numbers of persons under
16 years of age are less than the numbers over 65
years of age, a factor which has vital importance for
service planning. Paradoxically, whilst total numbers
of children are falling, the number of children with
multiple risk factors including poverty is increasing
(Knitzer, 2003) It is useful at this point to draw
together prevalence data for child communication
disorders with the caution that there are no common
measures, the nature of populations providing the
data varies and different cut off points have been
used to define caseness (Law et al., 1998) (see Table
I).
Taking an epidemiological perspective requires
practitioners to interpret such data in the light of
qualitative information about risk and outcomes
(Pencheon et al., 2001). However the ‘‘causal
network’’ between risks and outcomes is rarely
simple (Sameroff & Fiese, 2000) and not fully
understood. Thus, single factors such as increasing
age alone will not predict the presence or absence of
a particular disease but can only be associated with
an increased likelihood. To illustrate some of the
issues associated with the principles of epidemiology
let us consider the issue of speech and language
disorders in children in the context of poverty.
Epidemology: Child language and health
promotion
The growth of early childhood programmes in the
UK including Sure Start (Glass, 2001) has encour-
aged practitioners to examine the potential for
prevention of language difficulties as a way of
increasing ‘‘school readiness’’ and reducing the need
for tertiary services (intervention) in later years. Such
Table I. Prevalence for childhood speech and language problems.
Classification Prevalence in children
Fluency 4 – 5%1 (Anon, 2004)
Voice Hoarseness 6 – 23%1 (Anon, 2004)
Language (pre school) 2 – 8%1 (Anon, 2004)
Up to 7 years of age Range 1 – 19%, (5.9%, median prevalence estimate)
(Law et al., 1998)
Language delay (5 10th centile) at 20 – 24 months in disadvantaged
community
Range 18 – 31% (first figure based on parent report,
second figure based on direct testing) (Pickstone, 2004)
Phonology 8 – 9%1 (median prevalence estimates)
1ASHA American Speech & Hearing Association.
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programmes are provided in areas of disadvantage
and poverty. Poverty tends to be regarded as a risk
factor for developmental outcomes. It is recognized
that poverty is a relative term and that, for those who
are starving using the word ‘‘poverty’’ for the less
well off in the cities of the developed world would
seem inappropriate. However, the term child pov-
erty, currently referred to by many governments,
now encompasses families who live on low incomes
in comparison with the majority of the population
(Glass, 2001). Thus low income is defined (in the
UK) as an income below 60% of the contemporary
median incomes adjusted for household size (Pia-
chaud & Sutherland, 2002). Obviously the main
characteristic of poverty is low income, but it is also
strongly associated with poorer living standards, lack
of access to goods and services, poor housing
conditions and reduced educational levels within
the household. Notwithstanding the child’s genetic
make up which has been held to be responsible for
50% of variance in IQ outcomes (Parker, Greer, &
Zuckerman, 1988), the most important single factor
influencing developmental outcomes is usually held
to be the quality of parenting and the conditions of
the child’s physical surroundings (Gross, 1996). It is
within the home setting that the child learns to
communicate and interact with his environment and
those around him (Trivette, 2004). Research indi-
cates that poverty is associated with poorer
developmental outcomes (McLoyd, 1998; Bradley
& Corwyn, 2002) which means that children are less
prepared to start school and may have a higher risk of
long term learning and literacy problems. Establish-
ing the extent of developmental delay with
disadvantaged children is challenging. When tested
using standardised measures, some groups of chil-
dren from disadvantaged backgrounds are more
likely to be diagnosed with identifiable problems.
To some degree, this may result from under
representation of disadvantaged groups in the norm-
ing samples for tests (Qi et al., 2003). Some
researchers caution against the application of stan-
dardised measures developed with relatively
advantaged samples with children from disadvan-
taged situations because of the care needed in
interpreting the results (Fenson et al., 2000). Hence
the epidemiological conundrum: is the child normal
within this population, thus not requiring health
intervention? There may even be some practitioners
who make tacit allowances for children from poor
areas believing that the child is delayed in terms of
his language skills but that the degree of delay is in
line with expectations given the deprived circum-
stances. Thus they may be considered to be in the
normal range for that population and context.
Conversely others consider that the language delay
is preventable and requires intervention because it is
out of line with ‘normative data’ for the population as
a whole. Irrespective of the cause of the develop-
mental delay, there is no evidence whether such
children are less likely or more likely to gain benefit
from intervention. These children are often excluded
from research and screening studies. The same
factors which may preclude them may also prevent
them from taking part in intervention (Barnes,
2003).
Notwithstanding the challenges of interpreting test
scores for disadvantaged children, Ross and Roberts
(1999) collected longitudinal data from Canada and
confirmed that there was a higher incidence of
language and speech delay and impairment in
children from low income families with two and a
half times the expected rate of such. Their data
indicated that over 35% of children from low income
families have delayed development of vocabulary,
compared to 10% in higher income families at the
age of four to five years. Pickstone (2004) and others
have raised the question as to whether this develop-
mental language delay represents the tail of the
normal distribution curve for language skills or
whether the performance is qualitatively different in
some way.
Epidemiological study is not an end in itself. It
serves to contribute to the effort of improving health
of the population. Thus, knowing there is a
difference in the speech and language levels of those
who live in poverty should lead us to think of the
impact this should have on service involvement.
Furthermore, it should also lead to careful consid-
eration of models for how intervention might work
for children with multiple risks factors or conversely
for those who have higher resilience. There is an
assumption that in identifying children with delayed
language, effective intervention can compensate for
some risks. It can be argued that if there are no
interventions that can have an effect in reducing this
gap, then gathering such epidemiological data is
unhelpful. This is not dissimilar to screening.
Usually screening is used to identify conditions that
can be alleviated by timely interventions. Screening
children for language disorders when we are un-
certain whether interventions can be effective is still
rather a leap of faith. Most studies of interventions
with late talkers have tended to recruit families who
were self-selected, perhaps thereby more compliant
and frequently more affluent. Thus, they represent a
more advantaged group (Paul, Murray, Clancy, &
Andrews, 1997). Antoniadas and Lubker (1997)
called for epidemiology to be an essential tool for
establishing prevention programmes and evaluating
their impact and outcome in the area of speech and
language. Collecting even basic routine data could
add substantially to the epidemiological knowledge
base of communication disorders.
Epidemiology can therefore provide frameworks to
examine prevalence data for populations in order to
inform service planning. Such data depends upon
chosen cut off points for screening and thereby on
the definition of cases. Ideally, prevalence data would
be derived from longitudinal studies which are time
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consuming and expensive. Prevalence for the same
condition may vary according to the population
under scrutiny and needs to be interpreted with
considerable care. This said, an alternative method
to inform service planning would be to build models
of predictive risk (Law et al., 2000). Paradoxically,
although practitioners need to identify children who
will only progress with intervention, prevalence data
does not allow such predictions. A model of
predictive risk would allow known risk factors and
weight their importance (given research evidence) as
well as taking account of resilience in making a
prediction about the likely risk of long term needs. In
fact, Law et al. (2000) argue that we should work to
build a model rather than carrying out further
research to establish prevalence for different popula-
tions and conditions. This is in contrast to the view
that ‘‘Studies of the prevalence of speech and
language disorders and their long term impact
provide the foundation and rationale for studies of
the effectiveness of assessment and treatment proce-
dures. . .. . .. . .’’ (Logemann & Baum, 1998).
Epidemiology, acquired conditions and
intervention
Given the numbers of persons referred to speech and
language therapy in many countries over the last 20
years we should be better equipped to predict how
different populations react to their interventions.
The definition which opened this paper emphasized
that epidemiology studied ‘‘factors that influence the
distribution of disease or physiological condition’’,
thus there is an urgent need to consider methods of
collecting core data about the populations we serve.
The International Classification of Functioning
(ICF) which has replaced the ICIDH (World Health
Organization, 2002) offers an opportunity for col-
lecting such data. Whilst there is some information
on the numbers of persons who may be aphasic,
dysarthric and who stammer (Enderby & Philipp,
1986) there is little or no information on the related
consequences, i.e., the activity restriction or societal
loss. More information on the presentation of such
associated aspects would assist in determining the
types of intervention that may be needed and provide
a mechanism for collecting information on outcome
in order to determine consequences of intervention
or prevention programmes.
A retrospective study by Enderby and Pethram
(2001) analysed data collected on an information
system specifically designed for use by speech and
language therapists. The age, gender, medical
diagnosis and speech and language therapy diagnosis
associated with the referral of more than 73,000
clients to 11 speech and language therapy service
between 1987 and 1995 were reviewed. Whereas in
1987 just over one third (34.8%) of the patients
referred to these services did not have formal medical
diagnosis, and this was commonly associated with
children with speech and language delay or disorder,
by 1995 the group not having a particular medical
diagnosis had fallen to 17.2% of referrals. A better
understanding of the causes of communication
disorders, expanded paediatric services and earlier
primary investigation had improved the specificity of
the referrals. In 1987, 22.7% of the referrals with a
medical diagnosis to speech and language therapy
were associated with cerebral vascular disease.
However, by 1995 this had increased to 32%. The
most remarkable change was the increase in the
number of referrals for dysphagia which represented
only 0.94% of referrals in 1987 to 20.6% in 1995.
However the gender balance of referrals remained
remarkably constant over this period, 60% of the
referrals being male and 40% being female. Whilst
nearly half of all the referrals were aged less than five
years, the proportion of all referrals represented by
this age group had fallen slightly over these years.
This had been matched by an increase in the
proportion of the case load aged over 70 years and
is possibly related to the change in overall demo-
graphy. If one studies this information and relates it
to information published elsewhere associated with
the known incidence and prevalence of particular
speech and language disorders (e.g., dysphasia
associated with stroke, dysarthria associated with
Parkinson’s disease etc.) it is possible to investigate
unmet need. For example, it is suggested that there is
a prevalence rate of 160 persons per 100,000 with
Parkinson’s disease (Wade & Langton-Hewer,
1987). Investigating literature related to the sympto-
matology of Parkinson’s disease which is
summarized by Enderby and Davies (1989) would
suggest that 99 persons with Parkinson’s disease per
100,000 population would have a speech, language
or swallowing disorder. The evidence supporting the
value of speech and language therapy for those with
hypokinetic dysarthria is relatively robust, supporting
the appropriacy of referral.
Whilst the referrals of patients with this disorder
increased to all services studied in the nine year
period, it is interesting that no service was receiving a
referral rate indicating that all those within their local
population with Parkinson’s disease and associated
communication or swallowing disorder were being
referred to those services. However, there was an
improvement in referral rate as twice as many being
referred in the more recent years.
A better understanding of the impact of different
symptoms particularly associated with neurological
disease as well as an improved knowledge base and
appreciation of speech and language therapists by
neurologists, patients’ organizations and others has
led to earlier identification of communication and
swallowing disorders in this field. Thus it is likely
that some of the texts cited in Enderby and Phillip
(1986), that referred to the proportions of persons
with different neurological diseases having speech
and language problems, is now out of date. The
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referral patterns to services associated with more
unusual disorders are an indication of changing
recognition. Table II indicates aetiologies that cause,
in a proportion of patients, communication and
swallowing disorders.
We referred earlier to the issue of identification
of ‘‘case’’ being more problematic when the
definition of ‘‘normal’’ gives rise to debate. Societal
changes can also have an impact on what is
determined to be normal, for example persons
with reading problems were less disadvantaged/
advantaged when society did not demand a great
reliance upon this form of communication. Less
able readers at that time could have been seen in
the tail end of the normal curve rather than being
aberrant to the extent of requiring a diagnostic
label. It is possible that with the greater reliance on
all forms of communication, those who are less
able communicators will find themselves in the
position of being determined as cases worthy of
intervention or remediation.
In addition to all the above we would suggest that
gathering more consistent epidemiological allows
historical, comparative and hypothesis testing studies
which may illuminate this area and should underpin
and inform the delivery and type of services.
References
Anon (2004) Communication facts: Incidence and prevalence of
communication disorders and hearing loss in children – 2004
edition. American Speech and Hearing Association.
Antoniadis, A., & Lubker, B. B. (1997). Epidemiology as an
essential tool for establishing prevention programmes and
evaluation their impact on outcome. Journal of Communication
Disorder, 30, 369 – 244.
Barnes, J. (2003). Interventions addressing infant mental health
problems (Research review). Children and Society, 17, 386 –
395.
Berkman, L. F., & Kawachi, I. (Eds.) (2002). Social epidemiology.
Oxford: Oxford University Press.
Bradley, R. H., & Corwyn, R. F. (2002). Socioeconomic status
and child development. Annual Review of Psychology, 53, 371 –
399.
Bradshaw, J. (2002). Child poverty and child outcomes. Children
and Society, 16, 131 – 140.
Enderby, P., & Davies, P. (1989). Communication disorders:
Planning a service to meet the needs. British Journal of
Communication Disorders, 24, 301 – 331.
Enderby, P., & Philipp, R. (1986). Speech and language handicap:
Towards knowing the size of the problem. British Journal of
Disorders of Communication, 21, 151 – 165.
Enderby, P., & Petheram, B. (2002). Has aphasia therapy been
swallowed up? Journal of Clinical Rehabilitation, 16, 604 – 608.
Glass, N. (2001). What works for children? The political issues.
Children and Society, 15, 14 – 20.
Gross, D. (1996). What is a ‘‘good parent’’? The American Journal
of Maternal/Child Nursing, 21, 178 – 182.
Johnson, C. J., Beitchman, J. H, Young, A., Escobar, M.,
Atkinson, L., Wilson, B., Brownlie, E. B., Douglas, L.,
Taback, N., Lam, I. & Wang, M. (1999). Fourteen year
follow-up of children with and without speech/language
impairments; speech/language stability and outcomes. Journal
of Speech & Hearing Research, 42, 746 – 760.
Knitzer, J. (2003). Social and emotional development in young
low income children: What research tells us and why it matters
for early school success. Testimony presented at the Mailman
School of Public Health, Columbia University, New York. 29
January 2003.
Last, J. M. (1983). A dictionary of epidemiology. Oxford: Oxford
University Press.
Law, J., Boyle, J., Harris, F., Harkness, A., & Nye, C. (1998).
Screening for speech and language delay: A systematic review
of the literature. Health Technology Assessment, 2.
Law, J., Boyle, J., Harris, F., Harkness, A., & Nye, C. (2000).
Prevalence and natural history of primary speech and language
delay: Findings from a systematic review of the literature.
International Journal of Language & Communication Disorders,
35, 165 – 188.
Table II. Incidence and prevalence of acquired communication and swallow disorders.
Incidence of new cases
per 100,000 Prevalence per 100,000
Number of speech or
swallowing problems
Stroke 220 500 66 with communication disorder
120 dysphagia
Parkinsons Disease 20 160 69 dysarthria
30 dysphagia
Multiple Sclerosis 3.0 144 70 communication disorder
10 dysphagia
Dysphonia 28 28 28
Motor Neurone Disease 4 7 6
Myasthenia Gravis 3 30 10
Head injury Severe 10 – 15 228 longstanding problems 160
Moderate 15 – 20
Mild 250
Brain tumour 20 - 7
Encephalitis 7 - 5
Tourette Syndrome 0.5 40 20
Progressive supranuclear palsy - 6 6
Muscular dystrophy - 50 20
Guillain-Barre syndrome 2.5 - 2.0
Note: these figures are arrived at from a number of sources, primarily from publications of the Neurological Alliance Member Organizations
2002.
12 P. Enderby & C. Pickstone
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ech
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info
rmah
ealth
care
.com
by
McM
aste
r U
nive
rsity
on
10/2
8/14
For
pers
onal
use
onl
y.
Logemann, J. A., & Baum, H. B. (1998). Speech-language hearing
interventions in the schools: A public health perspective on
measuring their short term impact and long term impact.
Language, Speech and Hearing Services in the Schools, 29, 270 –
273.
Lubker, B. B. (1997). Epidemiology: An essential science for
speech language pathology and audiology. Journal of Commu-
nication Disorders, 30, 52 – 251.
McLoyd, V. (1998). Socioeconomic disadvantage and child
development. American Psychologist, 53, 185 – 204.
Paul, R., Murray, C., Clancy, K., & Andrews, D. (1997). Reading
and metaphonological outcomes in late talkers. Journal of
Speech and Hearing Research, 40, 1037 – 1047.
Parker, S., Greer, S., & Zuckerman, B. (1988). Double jeopardy –
the impact of poverty on child development. Pediatric Clinics of
North America, 35, 1227 – 1240.
Pencheon, D., Guest, C., Melzer, D., & Muir Gray, J. A. (Eds.)
(2001). Oxford handbook of public health practice. Oxford:
Oxford University Press.
Petheran, B., & Enderby, P. (2001). Demographic and epidemio-
logical analysis of patients referred to speech and language
therapy at 11 centres 1987 – 1995. International Journal of
Language and Communication Disorders, 36, 515 – 525.
Piachaud, D., & Sutherland, H. (2002). Changing poverty post-
1997. CASE paper 63. London: Centre for Analysis of Social
Exclusion, London School of Economics.
Pickstone, C. (2004). Targeted screening for delayed language in a
disadvantaged community. PhD thesis. University of Sheffield.
Tomblin, J. B., Records, N. L., Buckwalter, P., Zhang, X., Smith,
E., & O’Brien, M. (1997). Prevalence of specific language
impairments in kindergarten children. Journal of Speech,
Language & Hearing Research, 40, 1245 – 1260.
Townsend, P. (1962). The last refuge – a survey of residential
institutions and homes in England and Wales. London: Routledge
& Kegan Paul.
Trivette, C. M. (2004). Influence of home environment on the social-
emotional development of young children. Practice based research
analysis. Morganton, NC: The Puckett Institute.
Wade, D. T., & Langton-Hewer, R. (1987). Epidemiology of
some neurological diseases. International Rehabilitation Medi-
cine, 8, 129 – 137.
Why does it matter? 13
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onal
use
onl
y.