10 Percent and urban legend

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Being attracted by the premise that we only use 10% of our brains, the other night I watched "Lucy," even though my (mostly) always logical son insisted that the premise was untrue. Most interesting was how increasingly ineffective the plot became when you doubted its basis. (Sorry, Scarlett and Morgan. You both did fine jobs.)

Urban legend can sneak up on us. And the myth that says we use only 10 percent of our brains is especially pervasive, because it has been around so long and many people use it to their advantage. Another interesting take on the 10-percent-of-brain myth is Humans Already Use Way, Way More Than 10% of Their Brains at the Atlantic Monthly.

For more myths that are circulating, check out Snopes.com. It's a must-see in our twitter-fueled society.

The quantity 10 percent seems to be a handy number, though. There's the Ten Percent Law or Rule of 10's in ecology that says

...during the transfer of energy from organic food from one trophic level to the next, only about ten percent of the energy from organic matter is stored as flesh. The remaining is lost during transfer, broken down in respiration, or lost to incomplete digestion by higher trophic levels. (Wikipedia)

Statistics has the 10% condition which

states that sample sizes should be no more than 10% of the population. Whenever samples are involved in statistics, check the 10% condition to ensure you have sound results. Some statisticians argue that a 5% condition is better than a 10% condition if you want to use a standard normal model.

What I wonder is how 10 percent represents the population.  Guess that's why I'm not a statistician.

In elementary physics class we learned that efficiency seldom exceeds 20 percent.

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However, looking for example of inefficient devices, I'm finding some relatively efficient ones: Diode-pumped solid-state lasers that range from 1 to 60% efficient; autos that range between 15 and 35% efficient, and large AC motors that approach an amazing 93% efficiency (article is about centrifugal pumps).

Since we've wandered from the 10-percent topic, here's the ninety-nine rule:

The first 90 percent of the code accounts for the first 90 percent of the development time. The remaining 10 percent of the code accounts for the other 90 percent of the development time.

—Tom Cargill, Bell Labs (Wikipedia)

-- Marge