1. GIS and its applications in Health
دانشکده بهداشت دانشگاه علوم پزشکی تهران
آذر ماه 1384
ارايه دهنده: علي اکبر حقدوست

2. Definition John Snow project
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
GIS workshop in TUMS

3. ٍExample
GIS workshop in TUMS

4. Poisson Distribution Assumptions: Constant proportion in area
Independent distribution
GIS workshop in TUMS

5. Flying bombs strikes, south London
آيا بمبهاي آلمان در جنگ جهاني دوم آن گونه كه ادعا مي نمود قدرت تفكيك بالا در هدف قرار دادن مواضع را داشت؟
GIS workshop in TUMS

6. Flying bombs strikes, south London
Number of bombs in cells
# of cells 1 2 3 4 5
Total
observed
229
211 93 35 7
576
expected
227.5
211.3
98.2
30.4
7.1
1.54
GIS workshop in TUMS

7. Flying bombs strikes, south London
How can we test if the distribution of bombs was random?
GIS workshop in TUMS

8. 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
GIS workshop in TUMS

9. Nearest neighbor method
Minimum distance between observation I and (n-1)
Checks the distances between events A a b c d
GIS workshop in TUMS

10. Exponential (e)
GIS workshop in TUMS

11. Exponential (e)
GIS workshop in TUMS

12. R r
GIS workshop in TUMS

13. 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
GIS workshop in TUMS

14. Probability that at least one of n random points within the boundaries of the large circle falls within the boundaries of the small circle
GIS workshop in TUMS

15. Expected median, mean and variance based on these explanations (nearest neighbor analysis)
GIS workshop in TUMS

16. example آيا بين نقاط اين شكل هيچ ارتباطي وجود دارد؟
GIS workshop in TUMS

17. نقاط ضعف روش نزديكترين گزينه
Very large and small area (A) may reduce the significance
GIS workshop in TUMS

18. Boundary influence
GIS workshop in TUMS

19. 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
GIS workshop in TUMS

20. Original map
GIS workshop in TUMS

21. Cartogram
GIS workshop in TUMS

22. 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
GIS workshop in TUMS

23. Alternative method Case control approach
It means we can compare the spatial distribution of cases versus controls using Poisson models
GIS workshop in TUMS