Sunday, June 22, 2008

Should mileage units be gallons per 1000 miles?

Mileage is generally reported in miles per gallon (or kilometers per litre for the rest of the world). This seems to make sense. The consumer will want to know how far they will be able to get with the gasoline (petrol or paraffin for you non-Americans) they buy. Well, not exactly.

That might be a good metric if you have a fixed fuel budget and your travel plans followed from this. But most people buying automobiles aren't in that position. Most car shoppers have a certain amount of driving they need to do and are looking to keep their expenditures down. It should therefore make more sense to report mileage as the reciprocal (like gallons per 1000 miles for example).

While the two are mathematically equivalent, reciprocals scale differently. Most people will make bad decisions with the opposite ratio. Check out the video below for an explanation.

There are many examples of things like this all over. Let's take sunscreens for example. The SPF rating represents the equivalent protected exposure to UV rays in minutes to 1 minute exposure without the sunscreen. For example, 15 minutes of exposure to the sun while wearing SPF15 sunscreen gives you the same UV exposure as 1 minute unprotected.

But how much UV radiation is actually blocked? That can be calculated using the formula (1 - 1/SPF) * 100%
SPF5 blocks 80% of UV radiation.
SPF15 blocks 93% of UV radiation.
SPF45 blocks 98% of UV radiation.
SPF100 blocks 99% of UV radiation.

While something with a very high SPF rating may seem very impressive, I think anything higher than SPF15 is a waste.

And of course the way mileage is reported should be changed.


Eero said...

Actually in Europe and Canada the fuel efficiency is generally described as litres per 100 kilometers. And you're right, it's very easy to comprehend.

Elaine said...

Hi, Javier... was trying to find an Email for you - anyway, thanks for your kind words about the SONG FU song. I really appreciated your support, especially since I seem to have been trashed in the comments. :P If you're interested in some of my scratchings, I'm at