GIS and Health Geography What is epidemiology?. TOC GIS and health geography ◦Major applications...
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GIS and Health Geography What is epidemiology?. TOC GIS and health geography ◦Major applications for GIS Epidemiology ◦What is health (and how location
TOC GIS and health geography Major applications for GIS
Epidemiology What is health (and how location matters) What is a
disease (and how to identify one) Quantifying disease occurrence
Incidence vs prevalence Identifying the population Working with
small area data
Slide 3
GIS and health Geography A GIS can be a useful tool for health
researchers and planners because, as expressed by Scholten and
Lepper (1991): Health and ill-health are affected by a variety of
life- style and environmental factors, including where people live.
Characteristics of these locations (including socio-demographic and
environmental exposure) offer a valuable source for epidemiological
research studies on health and the environment. Health and
ill-health always have a spatial dimension therefore. More than a
century ago, epidemiologists and other medical scientists began to
explore the potential of maps for understanding the spatial
dynamics of disease.
Slide 4
Major applications for GIS 1. Spatial epidemiology 2.
Environmental hazards 3. Modeling Health Services 4. Identifying
health inequalities
Slide 5
Spatial epidemiology Spatial epidemiology is concerned with
describing and understanding spatial variation in disease risk.
Individual Individual level data small areas Counts for small areas
Recent developments owe much to: Geo-referenced health and
population data Computing advances Development of GIS Statistical
methodology
Slide 6
Framework for analysis Population is unevenly distributed
geographically. People move around (day-to-day movements; longer
term movements including migration). People possess relevant
individual characteristics (age, sex, genetic make- up, lifestyle,
etc). small areas People live in communities (small areas).
Slide 7
Why small area analyses? Provides a qualitative answer about
the existence of an association (e.g. between environmental
variable and health outcome). May provide evidence that can be
followed up in other ways.
Slide 8
Geographical correlation studies These studies typically
involve examining geographical variations in exposure to
environmental variables (air, water, soil, etc.) and their
association with health outcomes while controlling for other
relevant factors using regression.
Slide 9
Issues: Spatial misalignment
Slide 10
Issues: Uncertainty Frequency and quality of population data
(e.g. Census every 10 years). Spatial compatibility of different
data sets. Availability of data on population movements. Measuring
population exposure to the environmental variable. Environmental
impacts are often likely to be quite small (relative to, for
example, lifestyle effects) and there may be serious confounding
effects. Cannot estimate strength of an association; Ecological (or
aggregation) bias.
Slide 11
Issues: Best practices Allow for heterogeneity of exposure. Use
well defined population groups. Use survey data to help obtain good
exposure data. Allow for latency times. Allow for population
movement effects. (Richardson 1992)
Slide 12
Spatial epidemiology Dr. John Snows Map of Cholera Deaths in
the SOHO District of London, 1854
Slide 13
Major applications for GIS 1. Spatial epidemiology 2.
Environmental hazards 3. Modeling Health Services 4. Identifying
health inequalities
Slide 14
Environmental hazards Hazard Surveillance Hazardous agent
present in the environment Route of exposure exists Exposure
Surveillance Host exposed to agent Agent reaches target tissue
Agent produces adverse effect Outcome Surveillance Effect
clinically apparent
Slide 15
Environmental hazards GIS: Identify causal and mitigating
factors
Slide 16
Major applications for GIS 1. Spatial epidemiology 2.
Environmental hazards 3. Modeling Health Services 4. Identifying
health inequalities
Slide 17
ARIA (Accessibility/Remoteness Index of Australia) A generic
index of accessibility/ remoteness for all populated places in
non-metropolitan Australia A model which allows accessibility to
any type of service to be calculated from all populated places in
Australia
Slide 18
AIRA
Slide 19
Mortality rate of infants (1980-2001) Where do infants and
children die in WA? 1980-2002 Jane Freemantle, PhD. November
2004
Slide 20
SES and Heart disease Identifying health inequalities:
Well-known relationship 25% 50% of observed gradient due to risk
factors like smoking, hypertension and diabetes in lower
socio-economic groups (Marmot et al.,1997) Access to healthcare
(Bosma et al., 2005) Imbalance between workplace demands and
economic reward (Lynch et al.,1997) Poor education, lower levels of
health literacy, low birth weight (Marmot, 2000) Relationship may
vary with gender with the association thought to be stronger in
males (Thurston, 2005)
Slide 21
The Data Number of daily hospital discharges (Y) with Ischemic
Heart Disease (IHD) where admission had been via emergency room for
591 postcodes in NSW Every day from July 1, 1996 to June 30, 2001
Males and females 5-year age increments Denominator (N) obtained
from census Social disadvantage measured at postal area level using
the census-derived SEIFA ( Socio- Economic Indexes for Areas )
index
Slide 22
High values indicate social advantage SEIFA distribution in
NSW
Slide 23
NSW IHD rates
Slide 24
TOC GIS and health geography Major applications for GIS
Epidemiology What is health (and how location matters) What is a
disease (and how to identify one) Quantifying disease occurrence
Incidence vs prevalence Identifying the population Working with
small area data
Slide 25
The study of the distribution and determinants of health and
disease-related states in populations, and the application of this
study to control health problems. the product of [epidemiology] is
research and information and not public health action and
implementation (Atwood et al. 1997) epidemiologys full value is
achieved only when its contributions are placed in the context of
public health action, resulting in a healthier populace. (Koplan et
al. 1999) What is epidemiology?
Slide 26
(H. Shodell, Science 82, September, p. 50) E pidemiologists...
are like bookies of disease, stalking the globe to determine
point-spreads on which groups of people are most likely to get
which diseases. Part detective and part statistician, part
anthropologist and part physician, epidemiologists hope to track
down the agents of illness by deducing which of the differences
between peoples lie at the root of their distinctive disease
patterns.
Slide 27
Epidemiologic approaches DESCRIPTIVE Health and disease in the
community What? Who? When? Where? What are the health problems of
the community? What are the attributes of these illnesses? How many
people are affected? What are the attributes of affected persons?
Over what period of time? Where do the affected people live, work
or spend leisure time? ANALYTIC Etiology, prognosis and program
evaluation Why? How? What are the causal agents? What factors
affect outcome? By what mechanism do they operate?
Slide 28
Dorland's Illustrated Medical Dictionary (28th ed.): Health "a
state of optimal physical, mental, and social well-being, and not
merely the absence of disease and infirmity. Disease "any deviation
from or interruption of the normal structure or function of any
part, organ, or system (or combination thereof) of the body that is
manifested by a characteristic set of symptoms and signs...". What
are disease and health?
Slide 29
What is health Health, as defined in the World Health
Organization's Constitution, is "a state of complete physical,
mental and social well-being and not merely the absence of disease
or infirmity." Health is seen as more than just the absence of
disease, and depends upon a complex suite of factors, with location
taking the lead. A location is more than just a position within a
spatial frame (e.g., on the surface of the Earth or within the
human body). Different locations on Earth are usually associated
with different profiles: physical, biological, environmental,
economic, social, cultural and possibly even spiritual profiles,
that do affect and are affected by health, disease and
healthcare.
Slide 30
Location and health An example of how location matters and
carries with it other factors into play The body weight of infants
at birth is one readily available piece of data, and the
relationship between low birth-weight and maternal and child health
is a continuing line of research. In New York City, Sara McLafferty
and Barbara Tempalski have studied the spatial distribution of low
birth-weight infants and identified areas in which the number of
low birth-weight infants increased sharply during the 1980s. Their
results indicated that the rise in low birth-weight was closely
linked to women's declining economic status, inadequate insurance
coverage and prenatal care, as well as the spread of
crack/cocaine.
Slide 31
Location and health
Slide 32
Slide 33
TOC GIS and health geography Major applications for GIS
Epidemiology What is health (and how location matters) What is a
disease (and how to identify one) Quantifying disease occurrence
Incidence vs prevalence Identifying the population Working with
small area data
Slide 34
Manifestional criteria: labeling symptoms Manifestational
criteria refer to symptoms, signs, and other manifestations of the
condition. Defining a disease in terms of manifestational criteria
relies on the proposition that diseases have a characteristic set
of manifestations. This defines disease in terms of labeling
symptoms. Causal criteria: underlying pathological etiology Causal
criteria refer to the etiology of the condition, which must have
been identified in order to be employed. This defines disease in
terms of underlying pathological etiology. What is disease
Slide 35
Manifestational Criteria How do you identify a disease? The
Acquired Immunodeficiency Syndrome (AIDS) was initially defined by
the CDC in terms of manifestational criteria as a basis for
instituting surveillance. The operational definition grouped
diverse manifestations Kaposi's sarcoma outside its usual
subpopulation, PCP and other opportunistic infections in people
with no known basis for immunodeficiency. This was based on similar
epidemiologic observations (similar population affected, similar
geographical distribution) and a shared type immunity deficit
(elevated ratio of T-suppressor to T-helper lymphocytes).
Slide 36
Causal Criteria Human immunodeficiency virus (HIV, previously
called human lymphotrophic virus type III) was discovered and
demonstrated to be the causal agent for AIDS. AIDS could then be
defined by causal criteria.
Slide 37
Challenges with Disease Classifications A single causal agent
may have multiple clinical effects. Multiple etiologic pathways may
lead to apparently identical manifestations, so that a
manifestationally-defined disease entity may include subgroups with
differing etiologies. Multi-causation necessitates a degree of
arbitrariness in assigning a causative versus a contributing factor
to a disease. Not all persons with the causal agent develop the
disease.
Slide 38
Underlying Genetic Susceptibility Onset of disease Diagnosis of
disease Environmental & Behavioral Factors (Spatial dependence)
Physiologic Abnormalities Clinical disease Cause-specific mortality
X Sub-clinical disease The natural history of disease
Slide 39
TOC GIS and health geography Major applications for GIS
Epidemiology What is health (and how location matters) What is a
disease (and how to identify one) Quantifying disease occurrence
Incidence versus prevalence Identifying the population Working with
small area data
Slide 40
Measures of disease occurrence To study disease, we need
measures of its occurrence. Some measures of disease occurrence
Counts Prevalence Incidence Mortality
Slide 41
Epidemiologic approaches DESCRIPTIVE Health and disease in the
community What? Who? When? Where? What are the health problems of
the community? What are the attributes of these illnesses? How many
people are affected? What are the attributes of affected persons?
Over what period of time? Where do the affected people live, work
or spend leisure time? Each of the measures can be calculated for
different combinations of What? Who? When? and Where? Each of the
Ws needs to be defined carefully to get comparable measures across
a province or state, a nation, the world.
Slide 42
Prevalence The prevalence of a disease is the proportion of
individuals in a population with the disease (cases) at a specific
point in time: Prevalence is a proportion range of 0 to 1 Removes
the effect of total population size makes estimates from different
populations or over time more comparable.
Slide 43
Prevalence Often expressed as a percent (%) Prevalence * 100
Also often expressed as the prevalence per 1,000 or 10,000 or
100,000. Prevalence * 1,000 = prevalence per 1,000.