The Wall Street Journal concludes that, for most heterosexuals, the risk
of AIDS is something less than the risk of getting hit by lightning.
The Wall Street Journal statement is technically true, but highly
misleading. The Washington Times incorrectly restates the Wall Street
Journal by leaving off the qualifiers.
The basic problem with the Wall Street Journal statement is that it boils
down to "The risk of a small amount of X is smaller than a lifetime of Y".
Obviously, this statement can be true even if X is much more dangerous than Y.
As an example, the risk of dying from a 1000 mile car trip is less than
the risk of ever getting hit by lightning. This doesn't mean that driving
is safe, and in fact motor vehicle accidents kill about 50,000 Americans
a year. In addition, it is clearly wrong to say that the risk of dying
in a car accident is less than the risk of getting hit by lightning.
Thus, you can see that the Wall Street Journal statement sounds
impressive but doesn't really prove anything. In addition, the Washington
Times totally changes the meaning by removing the qualifiers "single act"
and "ever".
To get an accurate comparison of AIDS and lightning, we have to look at
the same time period. Since most people have sex more than once, it makes
more sense to look at the risk per year than the risk of a single act.
In a typical year, about 4000 Americans are diagnosed with AIDS obtained
through heterosexual contact, about 300 are struck by lightning, and about
90 die from lightning strikes. Thus, you can see that the risk of AIDS is
much higher than that of lightning; the AIDS rate is about the same as
the death rate from significant killers such as bronchitis or non-gas
poisoning or anemia or drowning or fires. (Are people needlessly worried
about the chances of dying in a fire?) If we exclude the half of
these AIDS cases attributed to heterosexual sex with partners who use IV
drugs, AIDS still is much more risky than lightning. Even if we exclude
in addition all the partners with unknown risk, AIDS still comes out ahead.
Therefore, comparisons between AIDS and lightning need to be examined very
closely. The Wall Street Journal, by using a carefully constructed
comparison, has a correct but misleading statement. Rephrases, such as
in the Washington Times, are wrong. To see the problems with these
comparisons, note that the risk of dying from a 1000 mile car trip is less
than risk of ever getting hit by lightning.
Appendix: calculations and references.
There were 94 lightning deaths in the US in 1980 out of 225 million
people. Thus, you have odds of about 1 in 2.4 million of dying of lightning
per year and 1 in 32,000 of ever dying of lightning (assuming a 75 year
lifespan). From a NOAA reprint, about 1/3 of lightning strikes are fatal,
so this would give odds of 1 in 800,000 of being struck by lightning per
year and about 1 in 10,000 of ever being struck by lightning.
(The NOAA, by the way, calls lightning "The underrated killer" and points
out that it kills more people in the US than tornadoes, floods, or
hurricanes.) There are about 2.4 motor vehicle fatalities per 100 million
miles travelled. Thus, in a 1000 mile trip, you have about 1 in 42,000 odds
of dying.
Lightning deaths from "The Injury Fact Book", fraction of fatal lightning
strikes from NOAA Reprint Vol 6 Number 2, 1976
(http://aws.com/lightnin.txt),
other US statistics from "Statistical Abstract of the United States, 1990"
The AIDS statistics are from the CDC's HIV/AIDS Surveillance Report,
Fourth Quarter 1992. I used 1992 statistics because the statistics from
1993 on are artifically inflated by a change in the AIDS definition, so
the 1992 statistics are the most accurate available.
Ken Shirriff:
[email protected]
This page:
http://www.righto.com/theories/lightning.html
Copyright 2000 Ken Shirriff.