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GIS in health
Generally, the objectives of a GIS are the management
(acquisition, storage and maintenance), analysis (statistical and spatial
modelling), and display (graphics and mapping) of geographic data. GIS is a
valuable tool to assist in health research, in health education, and in the
planning, monitoring and evaluation of health programmes and health systems.
Buffer Zones Creation
Another process that is very useful in health
research and planning is the benefit to the investigation of illness at or near
pollution and other hazardous sites, is the ability to create buffer zones
around the lines or points which represent those locations. The user can specify
the size of the buffer and then intersect or merge this information with disease
incidence data to determine how many counts of the illness fall within the
buffer. This technique has been used extensively for many conditions - e.g. to
understand the association between prevalence of childhood leukemia in northern
England and the proximity to nuclear power stations. This technique also
provides answers to questions such as "How many persons live within a 10 km
radius from a particular PHC or within how many kilometres from a community is a
First Referral Centre for attending to complex emergencies such as Caesarian
section during childbirth.
The generation of distance/proximity surface,
taking into account the distance, and the resistance to get there in terms of
costs which may be measured in rupees or time or even transportation means that
may not be available on the one hand, and the allocation modelling i.e.
assignment of every point of an area to the nearest set of designated features,
for example, the First Referral Centres are other geographic analysis tools that
can be used in health research and planning.
Spatial Analytic
Techniques
As discussed earlier, spatial variation in health related data
is well known, and its study is a fundamental aspect of epidemiology. There are
many types of spatial analysis : Point patterns - As the name implies, these are
dot maps, which display the distribution of health events as data locations. A
classic example is the identification of the source of cholera spread shown in
Figure 1. An alternative is the use of dynamic graphics such as associating the
dot map with a histogram of case occurrence. Selecting the upper tail of the
histogram automatically highlights the corresponding cases on the map thus
allowing characterisation of the regions by high incidence of the disease. Line
patterns Vectors or lines that aid in the analysis of disease diffusion and
patient-to-health care facilities flow. The lines can indicate the presence of
flow between two sub-regions or if the arrows have widths proportional to the
volume of flow, they can represent quantification. Francis and Schneider in 1984
designed an interactive graphic computer programme called FLOWMAP, to produce a
variety of maps of origin-destination data. Area patterns Chloropleth maps are
used to embed histograms into the polygons of maps. Another alternative is to
use stem-and-leaf plots to classify data before area pattern analysis. Surface
and contour patterns To overcome the limitation of administrative regions for
mapping, surface, and contour pattern maps allow the variable under study as
continuous process throughout the region. This analysis assumes that the event
is a continuous process and thus we get the maps, which are called isoline or
isopleths.
Temporal Analytic Techniques
Most of the techniques described earlier
can be used not only in health but in other areas as well. However, surveillance
of diseases requires continuous systematic collection and analysis of a series
of quantitative measurements. The detection and interpretation of changes in the
pattern of the constructed time series is very important and therefore this
presents a major challenge to the public health systems, as late detection of
the 'disease' may result in missed opportunities for intervention. Quality
Control Charts are useful methods for mapping surveillance data. The methods
commonly used for such mapping include - the Shewhart test, the simple
cumulative sum test and the V-mask. These methods are based on a comparison of
incoming values from the time series with constant values, usually defined
empirically from historical data. The advantages of such methods are that they
can provide graphic information, and as such can be incorporated into an
information system, helping the public health systems in the process. These are
techniques poorly developed in our country but are found widely used in the US,
France and some of the European countries. Statistical Monitoring
Epidemiologists like to use the concept of ratio of case numbers at a particular
time to past case occurrence using the mean or median. Based on this concept,
the Centers for Disease Control and Prevention of the US Government has
developed a technique in which the expected values are calculated based on a
five year average. Public health professionals directly report the incidence of
diseases to a central registry through a dedicated extranet environment and the
analysed maps are available readily, sometimes even in the public domain.
GIS for Advocacy and Communication in Health
Since mapping is
an excellent means of communicating a message clearly even to those who are not
necessarily familiar with the methodology, GIS can be used effectively with
leadership at various levels - panchayats, nagarpalika, districts, states and
national administration to convey the priorities, the problems and provide an
analysis and evidence based menu of options for programme implementation.
Mapping is also used in participatory learning and evaluation techniques for
community health projects. Small or large maps may be drawn or painted by groups
or individuals to represent the context in which they are living. These maps,
showing the location of the community structures - the houses, the wells, pumps,
latrines, roads, PHCs, sub-centres and anganwadi centres give participants a
wider view of where they are living. Such maps can help in discussion,
assessment, analysis and decision making.
These maps when posted in
public places and if updated provide a mirror for review and continuous updation
of decisions at the community level. Such efforts have been tried out in
different parts of India not only for decisions in the health sector but also
for critical decisions on siting of handpumps, sub-centres and even primary
schools.
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