GIS and its applications in Health

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GIS and its applications in Health

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Definition

• Lilienfeld 1976 in Fundamental epidemiology
• Epidemiology study of distribution of disease,
  or pathological condition in human populations
  and factors that influence this distribution
• What does mean distribution in above
  definition?
• We should explore the distribution in time and
  space
• John Snow project

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?Example
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Poisson Distribution

• Assumptions
• Constant proportion in area
• Independent distribution

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Flying bombs strikes, south London

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Flying bombs strikes, south London

• Number of bombs in cells

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Flying bombs strikes, south London

• How can we test if the distribution of bombs was
  random?

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Flying bombs strikes, south London

• This method is robust even for small sample
  numbers
• You can estimate variance even based on the group
  data
• Limitation
• It does not taking into account distances between
  events

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Nearest neighbor method

• Minimum distance between observation I and (n-1)
• Checks the distances between events

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Exponential (e)
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Exponential (e)
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Probability that a random point within the
boundaries of the large circle falls within the
boundaries of the small circle
Probability that a random point within the
boundaries of the large circle does not fall
within the boundaries of the small circle
Probability that n random points within the
boundaries of the large circle does not fall
within the boundaries of the small circle
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Probability that at least one of n random points
within the boundaries of the large circle falls
within the boundaries of the small circle
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• Expected median, mean and variance based on these
  explanations (nearest neighbor analysis)

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example
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• Very large and small area (A) may reduce the
  significance

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• Boundary influence

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Transformed map

• Uniform distribution is violated in nearly all
  situations.
• Redraw a map so that the density of the
  individuals at risk is equalized over the area
  under study, called a cartogram

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Original map
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Cartogram
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Limitations in using cartogram

• We need to have an accurate map to illustrate the
  population density
• The population at risk is not usually distributed
  exactly the same as the whole population
• It needs power full computer to generate a
  cartogram

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Alternative method

• Case control approach
• It means we can compare the spatial distribution
  of cases versus controls using Poisson models