And, according to new research, there’s another problem — confusing but widespread energy metrics, such as the ubiquitous miles per gallon or MPG. The paper, authored by Richard Larrick and two colleagues at the Fuqua School of Business at Duke University and just published in the journal Behavioral Science & Policy, not only argues that MPG is misleading, it lays out four separate principles to help make energy metrics more comprehensible to, er, humans.
“How people learn and how they make decisions is less of a mystery than ever before,” the authors note. But they say that that needs to be much more widely applied in the labeling of energy consuming products, ranging from cars to air conditioners.
The paper recommends steps such as putting energy use into context by comparing it to other things — for instance, your house used 10 percent more electricity than the average of your neighbors –and explaining how much total energy a given consumer product will use over its lifetime, or at least a significantly long time period. Another recommendation, meanwhile — which really draws out the problem with the MPG metric — is to switch from metrics that are based on energy efficiency to those based on consumption.
To show what this means, let’s explore further the problem with MPG. Most people probably do know their car’s MPG rating — but not necessarily how that translates into how much gas they actually use over 1,000 or 10,000 miles. And that’s not always straightforward – especially when it comes to comparing different vehicles.
To show as much, the researchers pose the following tricky question — which of the following options would most reduce the amount of gas consumed by a family’s driving?
- Trading in a very inefficient SUV that gets 10 miles per gallon (MPG) for a minivan that gets 20 MPG.
- Trading in an inefficient sedan that gets 20 MPG for a hybrid that gets 50 MPG.
If you’re like most people and chose B, you’re wrong.
The total increase in miles per gallon is clearly greater in option B — but that’s not the same as the overall reduction in gas consumed. “Driving 100 miles by the MPG values given above, our family can see that Option A reduces gas consumption from 10 gallons to 5 every hundred miles, whereas option B reduces gas consumption from 5 gallons to 2 over that distance,” explain Larrick and colleagues. Do the math for 10,000 miles or 100,000 miles and the ratios are the same, but the absolute number of gallons saved just grows and grows.
The point is not that we’re dumb or bad at math — rather, it’s that a metric like miles per gallon, which measures energy efficiency, can easily be confusing because it doesn’t give you a sense of the total energy consumed for various uses.
MPG is not the only such metric — though it’s the best known. For instance, air conditioning units use a rating called SEER (“seasonal energy efficiency rating”) which tells you how much cooling you get “per watt-hour of electricity.” It’s the same story — a metric based on efficiency, not the total amount of energy consumed.
“The main benefit of a consumption metric is that it does the math for people,” note Larrick and his co-authors.
Another recommendation from the study — giving a much broader time frame for how much energy a person will use with a given product — can also be elucidated with the example of gasoline consumption. The authors argue that if you tell people how much gas their car will use and how much that will cost over 100,000 miles of driving — where a small difference in MPG will add up to potentially big savings — they will become more inclined to choose the more efficient vehicle in a purchasing decision.
“If you’re thinking about switching to a new car, it’s good to give people the costs and benefits over a long distance, like what might be the life of the car, 100,000 miles,” says Larrick. “It gets people’s attention, and they realize, ‘that’s going to be a three to four thousand dollar difference between the two vehicles,’ and that’s the change that’s worth making.”
Fortunately, we’re getting better at all of this, Larrick says. The EPA’s new label for new cars, which came into use in 2011, leads with MPG but also provides gallons per 100 miles, annual fuel cost, and cost savings over five years “compared to the average new vehicle.”
“I think the new label is integrating a lot of the recommendations, but that’s a new development,” says Larrick. “It still has MPG.” It just has a lot of other stuff, too.
Overall, then, if you find trying to compute your personal energy use bewildering, be fair to yourself — the metrics out there may not be helping matters.