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

GIS workshop in TUMS Definition Lilienfeld 1976 in “Fundamental epidemiology” 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? time space We should explore the distribution in time and space John Snow project

GIS workshop in TUMS ٍ Example

GIS workshop in TUMS Poisson Distribution Assumptions: 1.Constant proportion in area 2.Independent distribution

GIS workshop in TUMS 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 Flying bombs strikes, south London Number of bombs in cells # of cells012345Total observed expected

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

GIS workshop in TUMS 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 Flying bombs strikes, south London

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

GIS workshop in TUMS Exponential (e)

GIS workshop in TUMS Exponential (e)

GIS workshop in TUMS R r

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 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 Expected median, mean and variance based on these explanations (nearest neighbor analysis)

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

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

GIS workshop in TUMS Boundaryinfluence Boundary influence

GIS workshop in TUMS 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 Original map

GIS workshop in TUMS Cartogram

GIS workshop in TUMS Limitations in using cartogram 1.We need to have an accurate map to illustrate the population density 2.The population at risk is not usually distributed exactly the same as the whole population 3.It needs power full computer to generate a cartogram

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