Using Numbers to Say What You Want

I’ve been more or less enjoying the articles over at 538, and not just the sports ones.  I also  started a new job as a researcher at the FAA back in the fall, so it jumped out at me when I saw a post titled “A Deadly 2014 For Air Travel Has Reversed Recent Safety Gains“.  My job isn’t to run numbers on these kinds of things, but I get emails with FAA news, and the ones I saw seemed positive.  Crashes were down.  Why is 538 telling me that safety gains have been reversed?  It’s because it picked one number to base the title on instead of all the other ones it mentions in the article.

Once you actually read the post, it’s clear that airline travel has gotten safer: the number of accidents per flight has dropped since 2005, and the number of deaths per flight have dropped even more.  The next graph, which plots share of accidents by share of traffic for different parts of the world, shows that there’s pretty much a perfect 1:1 ratio.  Places with more traffic have more accidents, which you would expect if there was just an even rate regardless of where you fly.  Those seem like positive things to note.

What’s odd is that other places have looked at the exact same numbers and made more positive conclusions.  Vox, for example, said it was a (surprisingly, given the media attention on the crashes) safe year for travel.  Verge notes that there were only 19 accidents, well below the recent average (a couple of the articles note that the exact numbers depend on your source, as different places use different data and count different things as crashes, but they all show the same trends).  The Washington Post said it was the safest year ever.

All of those more positive posts picked up on the somewhat implicit idea that if there are fewer crashes period, there will probably be fewer fatalities and other bad news.  This year is something of a fluke in that the crashes that did occur were big planes full of passengers that crashed in a bad way.  Large planes, per hours of flight, are safer overall than commuter flights or general (personal) aviation.  Airplane crashes in general are more survivable than you might guess.  I did a quick search and found a variety of numbers depending on the study and the timeframe, but the survival rate for any kind of crash is somewhere north of 60%.  Combined with how rare crashes are at all, and the fact that the rate is dropping, fatalities are very low and this year has been unfortunate.  Why 538 chose to emphasize the negative, I couldn’t say.

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