Wednesday, May 5, 2010

Worries about planes crashing

Consider for a moment what the average person does when they get off a plane.  They get their luggage, call for a ride or go to a bathroom that doesn't require contortionist training to use.  One very important thing they also do is call others to report that they have arrived safely.  It is important to note that people do not call others to report that they have successfully completed their commute home from work safely.  To compare the safety records of regular flights and car crashes from US data:

Chance of dying in a million plane flights:  .25
Chance of dying in a million days of normal car usage:  .33

So even if you fly every single day you are significantly more likely to die in a car crash than in a plane crash and *massively* more likely to be injured since car crashes often injure people - planes not so much.  It is more reasonable for people to want you to call them each evening to assure them you have not died in a car that day than it is for them to worry about your plane getting there safely.  Or is it?

Humans have a fear of the unknown and we tend to overestimate the risks of unusual behaviour drastically.  This could be considered irrational but really is a good heuristic.  We cannot take the time to do a full analysis of everything we do each day so we must make snap decisions.  Any time we face a decision with a big unknown we *should* guess high at the risk level.  The cost of guessing low is potentially catastrophic while the cost of guessing high is known and small.  Just as it is rational for all of us to buy insurance despite the cost of running insurance companies it is rational for us to worry more about risk in unfamiliar situations - it increases our expected lifetime at a cost we can afford to pay.

Given these things it isn't irrational to call people when you arrive from your plane trip.  Logically they do not need to be worried but their brains cannot avoid using their built in heuristic of fear in response to unfamiliar risk.  I am a pretty rational person and have some significant amount of self control but flying still makes me a bit nervous.  I doubt most people would even notice my reaction but I feel distinctly better when on the ground.  Rationally I know that driving across the city is more dangerous than a plane flight but I do not have perfect control over my responses to these things and my fear instinct kicks in while aloft.

Certainly you could argue that people should suppress their built in reactions when faced with concrete data that assures them that their gut instincts are wrong.  Like most things about human learning though changing your reactions requires time and familiarity and not dictated facts.  Fact is that an average day brings more risk of car crash death than a plane ride does of a plane crash death but until we all start flying as much as we drive we are going to continue to worry about plane crashes over car wrecks.  Correct it is not, but it is both unavoidable and entirely logical.

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