Nate Silver on the Risks of Airplane Terrorism
Over at fivethirtyeight.com, Nate Silver crunches the numbers and concludes that, at least as far as terrorism is concerned, air travel is safer than it’s ever been:
In the 2000s, a total of 469 passengers (including crew and terrorists) were killed worldwide as the result of Violent Passenger Incidents, 265 of which were on 9/11 itself. No fatal incidents have occurred since nearly simultaneous bombings of two Russian aircraft on 8/24/2004; this makes for the longest streak without a fatal incident since World War II. The overall death toll during the 2000s is about the same as it was during the 1960s, and substantially less than in the 1970s and 1980s, when violent incidents peaked. The worst individual years were 1985, 1988 and 1989, in that order; 2001 ranks fourth.
Of course, there is a lot more air travel now than there was a couple of decades ago. Although worldwide data is difficult to obtain, U.S. air travel generally expanded at rates of 10-15% per year from the 1930s through 9/11. If we assume that U.S. air traffic represents about a third of the worldwide total (the U.S. share of global GDP, which is probably a reasonable proxy, has fairly consistently been between 26-28% during this period), we can estimate the number of deaths from Violent Passenger Incidents per one billion passenger boardings. By this measure, the 2000s tied the 1990s for being the safest on record, each of which were about six times safer than any previous decade. About 22 passengers per one billion enplanements were killed as the result of VPIs during the 2000s; this compares with a rate of about 191 deaths per billion enplanements during the 1960s.
Why? Because over the past decade, the risk of airplane terrorism has been very low:
Over the past decade, according to BTS, there have been 99,320,309 commercial airline departures that either originated or landed within the United States. Dividing by six, we get one terrorist incident per 16,553,385 departures.
These departures flew a collective 69,415,786,000 miles. That means there has been one terrorist incident per 11,569,297,667 mles flown. This distance is equivalent to 1,459,664 trips around the diameter of the Earth, 24,218 round trips to the Moon, or two round trips to Neptune.
Assuming an average airborne speed of 425 miles per hour, these airplanes were aloft for a total of 163,331,261 hours. Therefore, there has been one terrorist incident per 27,221,877 hours airborne. This can also be expressed as one incident per 1,134,245 days airborne, or one incident per 3,105 years airborne.
There were a total of 674 passengers, not counting crew or the terrorists themselves, on the flights on which these incidents occurred. By contrast, there have been 7,015,630,000 passenger enplanements over the past decade. Therefore, the odds of being on given departure which is the subject of a terrorist incident have been 1 in 10,408,947 over the past decade. By contrast, the odds of being struck by lightning in a given year are about 1 in 500,000. This means that you could board 20 flights per year and still be less likely to be the subject of an attempted terrorist attack than to be struck by lightning.
In 2008, 37,000 people died in automobile accidents—the lowest number since 1961. Even so, that’s more than a 9/11 worth of fatalities every month, month after month, year after year.
There are all sorts of psychological biases that cause us to both misjudge risk and overreact to rare risks, but we can do better than that if we stop and think rationally.
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