GM Gets Shifty With Numbers

General Motors (GM) gets shifty with numbers in a recent print ad titled “Change is in the air.” I saw it on page 53 of The Economist magazine’s U.S. edition dated May 13-19, 2006.

The ad begins:

We’re changing a lot of things at GM these days. Even people’s minds. Take the environment. Today we lead the industry in the number of models that get an EPA estimated 30 mpg or better on the highway. More than Toyota or Honda.

The ad does not mention that GM also leads the industry in the number of models that get an EPA estimated 29 miles per gallon or less. What? It turns out GM can win either side of this issue because GM has significantly more models than any other car company. In other words, “We have the most models above 30 mpg! We have the most models below 30 mpg! How? Because we have, by far, the most models!”

To make a more meaningful comparison, let’s look at the percentage of each car company’s models that get 30 mpg or better on the highway. Using the Environmental Protection Agency’s data for model-year 2006 cars, we find that 14.1% of GM’s models get 30 miles per gallon or better on the highway. That’s less than half the 30-mpg+ percentage of either Toyota (36.7%) or Honda (36.4%). It’s also less than the average 30-mpg+ percentage across all car models in the database (17.3%).

Thus, GM’s “leadership” doesn’t look so good from this, more meaningful angle. (For those who remember the Arizona State University ad that claimed superiority over Stanford and several Ivy League schools in the number of freshmen who were top-10% high schoolers, this GM ad is abusing numbers in a similar way.)

For the record, below is a ranking of car brands by the percentage of models that get 30 mpg or better on the highway. You can create this analysis from the 2006 EPA data file using an Excel PivotTable. The original data represents each GM brand separately, but I have added a line at the end that totals the GM brands listed in the ad (Buick, Cadillac, Chevrolet, GMC, Hummer, Pontiac, Saab, and Saturn).