source: Class Slides for the MPG Illusion These slides may be used without copyright approval Please acknowledge as the sourcehttp://

source: MPG Quiz Assume that a person drives 10,000 miles per year and is contemplating changing from a current vehicle to a new one. Rank the following five pairs of old and new vehicles in order of their benefit to the environment (i.e., which new car would reduce gas consumption the most compared to the original car). Use 1 for the largest savings and 5 for the smallest savings.

source: MPG Quiz Change in Vehicle Pairs (Old Vehicle to New Vehicle) Rank in Gas Savings? A) 18 MPG to 28 MPG B) 16 MPG to 20 MPG C) 34 MPG to 50 MPG D) 22 MPG to 24 MPG E) 42 MPG to 48 MPG Rank the gas savings from MPG improvements for a car driven 10,000 miles (1 = largest, 5 = smallest)

source: MPG Quiz – Typical Ranks Change in Vehicle Pairs (Old Vehicle to New Vehicle) Rank in Gas Savings? A) 18 MPG to 28 MPG2 B) 16 MPG to 20 MPG4 C) 34 MPG to 50 MPG1 D) 22 MPG to 24 MPG5 E) 42 MPG to 48 MPG3 Rank the gas savings from MPG improvements for a car driven 10,000 miles (1 = largest, 5 = smallest)

source: MPG Quiz – Actual Ranks Change in Vehicle Pairs (Old Vehicle to New Vehicle) Perceived Rank in Gas Savings (Mean) Actual Rank in Gas Savings Actual Reduction in Gas Consumption per 10,000 miles A) 18 MPG to 28 MPG B) 16 MPG to 20 MPG C) 34 MPG to 50 MPG D) 22 MPG to 24 MPG E) 42 MPG to 48 MPG Rank the gas savings from MPG improvements for a car driven 10,000 miles (1 = largest, 5 = smallest)

source: Alernative Quiz

source: Judgments of Car Fuel Efficiency Standard measure in US – Miles per gallon (MPG) What does it measure? – Useful for knowing range of gas tank What question do you want to answer when buying a car? – How much gas you’re going to use » Cost of gas » Greenhouse gases (burning 1 gallon of gas releases 20 pounds of carbon)

source: The Problem with MPG Consider three people who each drive 100 miles per week. Their current vehicles have the following fuel efficiency: – Person A: 10 MPG – Person B: 16.5 MPG – Person C: 33 MPG

source: The Problem with MPG Each driver trades in his or her car for a more efficient car – Person A: 10 MPG -> 11 MPG – Person B: 16.5 MPG -> 20 MPG – Person C: 33 MPG -> 50 MPG Who saves the most gas over 100 miles? Result: Each trade-in reduces gas consumption by the same amount – In each case, the new car saves 1 gallon per 100 miles – The new car eliminates 1 ton of carbon per 10,000 miles

source: Calculating Gas Savings To know gas consumption and gas savings, one needs to divide the distance one drives by MPG – Gas consumption = Distance / MPG – Conclusions Gas savings are not a linear function of MPG The relationship between gallons consumed and MPG is curvilinear Gallons consumed can be abbreviated “Gallons per Mile” or “GPM” for short The following graph and tables illustrate the relationship

source: Gas Consumption as a Function of MPG

source: Miles Per GallonGallons Per 100 Miles Gallons Per 10,000 Miles Converting MPG to GPM – Equal MPG This table displays total gas consumption based on equal increases in MPG

source: Miles Per GallonGallons Per 100 Miles Gallons Per 10,000 Miles Converting MPG to GPM – Equal GPM This table displays MPG improvements that yield equal decreases in gas consumption (1 gallon per 100 miles or 100 gallons per 10,000miles)

source: Summary of Research The following slides summarize the results of research published by Larrick & Soll (Science, 2008)

source: Study 1: Ranking Improvements (n = 77, Larrick & Soll, Science, 2008) Task: Rank gas savings from MPG improvements for a car driven 10,000 miles (1 = largest, 5 = smallest) Change in Vehicle Pairs (Old Vehicle to New Vehicle) 34 MPG to 50 MPG 18 MPG to 28 MPG 42 MPG to 48 MPG 16 MPG to 20 MPG 22 MPG to 24 MPG Perceived Rank in Gas Savings (Mean)

source: Study 1: Ranking Improvements (n = 77, Larrick & Soll, Science, 2008) Change in Vehicle Pairs (Old Vehicle to New Vehicle) Perceived Rank in Gas Savings (Mean) Actual Rank in Gas Savings Actual Reduction in Gas Consumption per 10,000 miles 34 MPG to 50 MPG MPG to 28 MPG MPG to 48 MPG MPG to 20 MPG MPG to 24 MPG Task: Rank gas savings from MPG improvements for a car driven 10,000 miles (1 = largest, 5 = smallest)

source: Study 3: Fleet Decision (n = 171 in a national survey, Larrick & Soll, Science, 2008) A town maintains a fleet of vehicles for town employee use. It has two types of vehicles. – Type A gets 15 miles per gallon. – Type B gets 34 miles per gallon. The town has 100 Type A vehicles and 100 Type B vehicles. Each car in the fleet is driven 10,000 miles per year. They can afford to replace one type of vehicle with a hybrid (H) option. – Type AH gets 19 miles per gallon. – Type BH gets 44 miles per gallon.

source: Study 3: Fleet Decision (n = 171 in a national survey, Larrick & Soll, Science, 2008) They can afford to replace one type of vehicle with a hybrid (H) option. GPM frame: Participants saw both MPG and “Gallons per 100 miles” 1) Replace the Type A vehicles (6.67 gpm) with Type AH that gets 5.26 gpm 2) Replace the Type B vehicles (2.94 gpm) with Type BH that gets 2.27 gpm MPG Frame 1) Replace the Type A vehicles (15 mpg) with Type AH that gets 19 mpg 2) Replace the Type B vehicles (34 mpg) with Type BH that gets 44 mpg

source: Study 3: Fleet Decision (n = 171 in a national survey, Larrick & Soll, Science, 2008) They can afford to replace one type of vehicle with a hybrid (H) option. GPM frame: Participants saw both MPG and “Gallons per 100 miles” 1) Replace the Type A vehicles (6.67 gpm) with Type AH that gets 5.26 gpm 2) Replace the Type B vehicles (2.94 gpm) with Type BH that gets 2.27 gpm MPG Frame 1) Replace the Type A vehicles (15 mpg) with Type AH that gets 19 mpg 2) Replace the Type B vehicles (34 mpg) with Type BH that gets 44 mpg Result: 75% of participants incorrectly favored Option 2 Result: 64% of participants correctly favored Option 1

source: Specific Policy Implications For car purchase decisions, provide a measure of efficiency that is volume of gas divided by distance – Europe and Canada use liters per 100 kilometers – United States What should the US use as a basic “gallons per mile” measure? Where should it be reported? Example of an online GPM calculator for new cars –

source: Improving Decision Making How can psychology be used to improve a range of decisions? – “Choice architecture” principles from Nudge (Thaler & Sunstein, 2008): Set defaults to encourage people to make more prudent choices. Provide explicit feedback to help people recognize when they are doing well and when they are making mistakes. Help people see the connection between their options and what choices will actually make them better off. Design incentives so that benefits and costs are clear. Design “forgiving” systems that take into account the fact that people will make mistakes. Structure complex choices so they are easier for people to understand.

source: Improving GHG Decisions What can psychology contribute to reducing greenhouse gas emissions? – Car choice – Car use – Other transportation What new tools could help people make decisions that reduced greenhouse gas emissions in general?

source: Useful Links and References Larrick, R. P., & Soll, J. B. (2008). The MPG Illusion, Science, 320, Thaler, R. H., & Sunstein, C. (2008). Nudge. New Haven: Yale.