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Survivorship bias
June 1, 2020
 
Ever see one of those Facebook posts that shows kids riding in the back of a pickup truck, maybe back in the 1950s, with commentary something like, “We didn’t wear seat belts and we turned out just fine.”? Such posts are clearly a criticism of an over-reaching “nanny state” that supposedly legislates away personal freedom by requiring silly things like seat belts.

But you know what? The kids who were killed because they were not wearing seatbelts are not posting on Facebook. Well, duh, you might say. But how many people reading those posts actually stop to think of this critical fact? Very few, I wager.

This example is a literal illustration of survivorship bias: only the survivors are around to post on Facebook, and only they have the last word on the topic. Unless, that is, you can see through that bias to a bigger world.

The examples are everywhere, yet we rarely stop to consider them. Ever see a late-night infomercial in which the host interviews someone who lost their shirt flipping houses with no money down? Unlikely, to say the least.

“Grandma smoked a pack of cigarettes a day and lived to be 102.” Well, what happened to Grandpa, who also smoked a pack of cigarettes a day? He died at 49. Oh.

About 1.6% of all NCAA (college) football players ever play in the National Football League.(1) We see the success stories on the gridiron, we don’t see the 98.4%.  Yet how many young football players pin their hopes on an unlikely NFL career, often downplaying the more important task of doing well in the classroom along the way? As a university professor who has taught at three universities with top football teams, I can confirm this phenomenon is very prevalent among that type of student. Incredibly high failure rate? Don’t want to hear it.

And while we are on the topic of career choices, a similar mental calculation often goes on among budding entrepreneurs. For example, we observe that a number of very successful entrepreneurs dropped out of college, e.g., Mark Zuckerberg and Bill Gates. I think by now you are ahead of me: What we do not see are the entrepreneurs who dropped out of college and did not succeed, and there are certainly many of those! One could push faulty reasoning even further: Both Zuckerberg and Gates dropped out of Harvard. So the key to success is to get admitted to Harvard and then drop out??  Again, should we ever manage to get accurate data on those who did so, the success stories I am sure would be 0.0001% or thereabouts of the entrepreneurial population.

We would all make more informed, better decisions if we had the relevant facts at hand – and if we consciously are aware of, and combat, the biases that often stop us from doing so. Next time you run into a scenario like any of those I have just mentioned, stop for a moment and see whether you can answer the “flip” questions.  For example, What if the opposite were true? Is there something major here that I am not seeing? Is this a floating piece of ice, or is it the tiny top of a massive iceberg? In other words, try to flip the issue on its head and see what you find.
 
In the meantime though, and I’m not being a nanny here, you might want to buckle up.

Notes:
(1) Source: http://www.ncaa.org/about/resources/research/estimated-probability-competing-professional-athletics

For an earlier version of this essay, more focused on finance, see:
https://www.bloombergprep.com/blog-posts/survivorship-and-related-biases

If you want to read previous newsletters, click “View this email in your browser” at the top. Then in the upper left-hand corner, you can click on “Past Issues”.
 
Copyright © 2020 John S. Howe, All rights reserved.

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