251. Survivorship Bias's Fatal Flaw

<p>There’s an important bias to avoid: Survivorship bias. Unfortunately, people who might otherwise do something with their lives hide behind survivorship bias. Just as important as knowing when survivorship bias matters is knowing when survivorship bias does not matter. Survivorship bias has a fatal flaw.<!--more--></p> <p><!-- /wp:paragraph --><!-- wp:heading {"level":3} --></p> <p><!-- /wp:paragraph --><!-- wp:heading {"level":3} --></p> <h3>Example: Abraham Wald avoided survivorship bias to bring back more survivors</h3> <p><!-- /wp:heading --><!-- wp:paragraph --></p> <p>In WWII the US military was trying to improve their planes. Each time a plane came back from a mission, they made a record of the bullet holes. Since most bullet holes were on the wings and tails of the planes, the military concluded they needed to add more armor in the wings and tails.</p> <p><!-- /wp:paragraph --><!-- wp:paragraph --></p> <p>But statistician Abraham Wald <a href= "https://mcdreeamiemusings.com/blog/2019/4/1/survivorship-bias-how-lessons-from-world-war-two-affect-clinical-research-today"> said</a>, No – that’s not where you want to add more armor. You want more armor around the engine.</p> <p><!-- /wp:paragraph --><!-- wp:paragraph --></p> <p>That seemed weird. Their map of bullet holes showed very little damage to the engine compartment.</p> <p><!-- /wp:paragraph --> <!-- wp:image {"id":7565, "align": "center"} --></p> <div class="wp-block-image"><img class="wp-image-7565 size-medium" src= "http://kadavy.net/wp-content/uploads/2021/02/Survivorship-bias-abraham-wald-plane-350x261.png" alt="" width="350" height="261" /> </div> <p><!-- /wp:paragraph --><!-- wp:paragraph --></p> <p>What Wald noticed that the military hadn’t noticed is they were only seeing bullet holes on planes that returned from missions. The bullet holes they weren’t seeing were the bullet holes on planes that did <em>not</em> return. And the bullet holes on planes that did not return were the ones bringing the planes down.</p> <p><!-- /wp:paragraph --><!-