Thursday, August 27, 2009

Miles to go before I sleep

Math can make your head spin. I was reading Seth Godin's blog (catching up on his blog actually, but whatever) and came upon his post, "Not so good at math." He reprinted the classic miles-per-gallon example, comparing Suburbans to Priuses, in which two alternative performance improvements are proposed and you are asked which is the better choice.

His point is to remind marketers that the ordinary consumer is, as he puts it "not wired for arithmetic. It confuses us, stresses us out and more often than not, is used to deceive."

Have you ever heard someone say, "numbers don't lie"? Yeah, right. Numbers may not lie, but they sure can obfuscate some cold hard facts, especially when wielded by a master.

To me, it's like the age-old question is lying by omission lying?

The mpg example goes like this:

You want to reduce gasoline consumption and, lucky for you, there are only two kinds of cars in the world. Half of them are Suburbans that get 10 miles to the gallon and half are Priuses that get 50.

If we assume that all the cars drive the same number of miles, which would be a better investment:

  • Get new tires for all the Suburbans and increase their mileage a bit to 13 miles per gallon.
  • Replace all the Priuses and rewire them to get 100 miles per gallon (doubling their average!)

That seems like a no-brainer, right? Well, except for the fact that you know there's a trick in there somewhere.

This is a bit of a mind bender, but think about it this way (since you've obviously figured out that the answer is NOT replacing the Priuses) — if you drive 25 miles in an "unmodified" Suburban, you'll go through 2 1/2 gallons of gas, while going through only 1/2 a gallon driving the same distance in a Prius. That's easy enough, right? Okay, stick with me. If you modify the Prius, doubling the gas consumption efficiency, and drive another 25 miles you'll save a whopping 1/4 gallon of gas.

But, if you modify your Suburban, improving gas consumption efficiency only by a third, and drive another 25 miles, you'll save 1/2 gallon of gas (actually, a little bit more). Twice as much as you would save modifying the Prius.

Basically, the Prius is already so efficient, that making it more efficient doesn't save you that much. But the Suburban is so inefficient, that even making it a little more efficient makes a big difference.

To Seth's point, however, who of us ordinary consumers would jump to that conclusion first? And no, Dad, you are not an ordinary consumer.

1 comment:

Ben Weiss said...

That's why gallons per mile (or gallons per 100 miles) is a much more meaningful way to think about this.

The Prius uses two gallons per 100 miles, and the Hummer uses ten gallons per 100 miles. So if the choice is to make the Prius use one gallon per 100 miles, or make the Hummer use seven gallons per 100 miles, clearly the latter is the better choice.

Or you could just drive an electric car :)