Once again, the Mythbusters have shown that they are careless with basic mathematics. They have shown that they can’t reliably calculate percentages, which makes me worry about all of other math that they do. They described dimpled golf balls as going 37% farther, when they actually went 61% farther!
In Episode 127 – Dirty vs. Clean Car they test whether a dirty car will get better mileage than a fast car. As part of this test they measure how much farther a dimpled golf ball will go compared to a smooth golf ball. They describe the results in three different ways:
- The dimpled golf balls appear to go about twice as far
- The dimpled golf balls go about 893 feet compared to about 556 feet for the smooth golf balls (those are either exactly what they said or very close)
- The dimpled golf balls go 37% farther than the smooth golf balls
This series of statements seem suspicious. Twice as far would be 100% farther, which is a long way from the 37% farther that they calculated. The ‘twice as far’ was just an eyeballed estimate, but the calculation of 37% farther seems improbably inconsistent with this estimate.
Looking at the numbers and applying standard percentage calculations we see that the percentage change from non-dimpled (556 feet) to dimpled (893 feet) balls was:
(893 / 556) * 100% – 100% = 60.6%
The multiplication by 100% is needed to change the result from a simple ratio to a percentage, and then we subtract 100% because we want to calculate the percentage increase.
The result of 60.6% shows that their eyeballed estimate was actually reasonably good, but their math was terrible. So, where did the 37% number come from? Let’s try to find out.
Given those same numbers we could reverse the numbers to see the percentage change from dimpled (893 feet) to non-dimpled (556) feet balls:
(556 / 893) * 100% – 100% = –37.7%
It’s not perfect (37.7% should be rounded to 38%) but it looks like this is the calculation that they did. They calculated one thing (the non-dimpled balls travelled about a 37% shorter distance) but said something else (the dimpled balls travelled about 37% farther). The two statements are quite different.
The simplest example of this non-transitivity is if we have two people, one who is three feet tall and the other who is six feet tall. We can say that the tall person is 100% taller, or we can say that the short person is 50% shorter. Different numbers for different statements.
Adam and Jamie need to think more about what they’re saying, or get better fact checkers.