Friday, July 23, 2010

Past Performance Does NOT Predict Future Outcome

"The Black Swan" is a very interesting book. Lots of things to think about. You'll hear people getting mileage out of Nassim Nicholas Taleb without  referencing "The Black Swan" directly but (IMHO), if you've read a strength and conditioning blog post about logical fallacies or confirmation bias over the past couple years, it's a pretty good bet they've read this book.

The Black Swan: Second Edition: The Impact of the Highly Improbable: With a new section: "On Robustness and Fragility"
...the Problem of Induction or Problem of Inductive Knowledge (capitalized for its seriousness) - certainly the mother of all problems in life. How can we logically go from specific instances to reach general conclusions? How do we know what we know? How do we know that what we have observed from given objects and events suffices to enable us to figure out their other properties? There are traps built into any kind of knowledge gained from observation.

Consider a turkey that is fed every day. Every single feeding will firm up the bird's belief that it is the general rule of life to be fed every day by friendly members of the human race "looking out for its best interest," as a politician would say. On the afternoon of the Wednesday before Thanksgiving, something unexpected will happen to the turkey. It will incur a revision of belief.

...Let us go one step further and consider induction's most worrisome aspect: learning backward. Consider that the turkey's experience may have, rather than no value, a negative value. It learned from observation, as we are all advised to do (hey, after all, this is what is believed to be the scientific method). Its confidence increased as the number of friendly feedings grew, and it felt increasingly safe even though the slaughter was more and more imminent. Consider that the feeling of safety reached its maximum when the risk was at the highest! But the problem is even more general than that; it strikes at the nature of empirical knowledge itself. Something has worked in past, until - well, it unexpectedly no longer does, and what we have learned from the past turns out to be at best irrelevant or false, at worst viciously misleading.

- The Black Swan: Second Edition: The Impact of the Highly Improbable: With a new section: "On Robustness and Fragility" (pp. 40-41) 
Ever heard these?

"I'm going to go back to doing good mornings [or Smolov, etc, etc, etc...], because the last time I did them, my squat numbers skyrocketed."

"If it ain't broke, don't fix it."

"I don't understand what went wrong. I did EVERYTHING THE SAME AS BEFORE!"

Yeah, me too.
Change is inevitable. All things are impermanent. Even if you want to do the same program to get the same results you got before, you could be disappointed because you are not the same you. This is a tough pill to swallow. We think that past performance is a good predictor of future outcomes, but we know that it's not true because car accidents, the stock market, and drilling rigs tell us it's not true ALL THE TIME. We know that things change. Sometimes, "if it ain't broke" means "it ain't broke... yet".

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