Isn't the question of scale related to what one is trying to measure? In a
simplified view of disasters there are two scales of importance that I see:
those that measure the magnitude of either physical or sociological impacts.
There are reliable scales that measure physical properties of hazards such
as the Richter scale, wind speed, tidal surges, etc.
Defining sociological impacts of disasters is not so easy. Attempts to
estimate the severity of impact that are based on count data (number of
people, number of structures) have not proven themselves, because the
comparison among disasters depends on pre existing conditions.
It seems to me that conditional probabilities take the pre existing
conditions into account. Conditional probability is the proportion of units
(e.g., people, structures, revenue) affected out of those exposed
in the disaster (this is the epidemiologic measure of "relative risk"). Once
the risk has been determined for two or more disasters the magnitudes of
disasters can be compared by taking the prevalence of affected units in the
population as a whole into account (this is the epidemiological measure of
"attributable risk").
For example, and much simplified:
Hurricane X had a swath of 40 X 60 miles in which 250,000 out of 1,000,000
(25%) were affected. These 1,000,000 represent 0.05% of Country Z's total
population, so
the impact of this disaster was 0.25(0.05)=0.0125.
Volcano Y affected 1,000 square miles in which 90,000 out of 100,000
(90%) were affected. These 100,000 represent 0.005% of Country Z's total
population, so
the impact of this disaster was 0.90(0.005)=0.0045.
The comparison of the two disasters is then the ratio of the two, and would
suggest that the impact of Hurricane was 0.0125 / 0.0045 = 2.8 times greater
than the volcano.
Food for thought?
Yours, Sebastian
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VetMB, Ph.D., DACVIM, DACVPM
3910 Morehouse Road
West Lafayette, IN 47906
Tel.: (765) 497-1984
Fax.: (765) 463-4493
Animal Management in Disasters (http://www1.mosby.com/)
Rescuing Rover (Http://www.lib.purdue.edu/thepress)
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