We always hear the base rates for these things. For example, the CDC (
http://wonder.cdc.gov/wonder/PrevGuid/m0052833/m0052833.asp ) says an
average of 82 people died from lightning in the US between 1980-1995.
But we don't know how many man hours outside was required for this. If
during the same time the US average of 250 million people or so spent an
average of 10 minutes outdoors in thunderstorms per year (low estimate),
this would be 25 million thunderstorm man hours per 82 deaths and the
risk of death would be 1 death per 300,000 thunderstorm man hours. This
would be the important statistic governing the dangerosity of lightning
because it estimates how much risky behavior (exposing oneself to
lightning) results in each death. I'm guessing these data just to show
how the calculation is done. To estimate the dangerosity of caving,
we'd need to know how many man hours were spent underground for several
years and the corresponding number of fatal accidents. To be useful,
we'd also want to separate out horizontal vs vertical caving, cave
diving, and caving by non-cavers. As in ALL cases involving injury, it
is also obligatory to separate out factors like drinking, though in my
experience this is not as common as, say, drinking and driving, which
produces something like a 20-fold modifier in the number of deaths per
driving hour or driving mile.
You need to do the same thing to assess the danger of driving vs flying
(also do per mile), comparing traveling abroad vs in the US or comparing
the risks of living in certain cities, and other things that people talk
about a lot. I know I once tried to work out flying vs driving. Per
hour, it seems that flying is more dangerous. Per distance, cars are.
For something like smoking that causes an accumulated risk of early
death, it may be more useful to compare time smoked to time lost. (It's
4:1.)
Speaking of flying and caving, I once was going to go on a flying trip
in a single-engine plane, but my pilot was on the cave-rescue call list
in Bloomington, Indiana and was called out on a search. They found the
lost boys drunk in the back of a cave, burning their shirts for light.
It was Y2K morning. They'd gone out to celebrate the millennium. SO,
obviously, drinking and Y2K can (via caving) cause not flying. I'm sure
the base rate and the per flight rate of this is very small.
Gregg
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