Revisiting the Prius Effect: Data Don’t Change Systems, People Do

Back in 2009, I thought about “feedback leads to reduced energy use” and called it the Prius effect, in honor of an observation by Carrie Armel at Stanford, quoted in an article by Dan Charles (Science 14 August 2009: Vol. 325 no. 5942 pp. 804-811):

“The next big force for behavioral change may be technology that brings consumers face-to-face with their energy consumption. A simple version of such energy feedback is the dashboard of a Toyota Prius hybrid car, which displays the rate at which the car is burning gasoline. No one has carried out a controlled study of how drivers react to it, but ‘every person I know who has a Prius, they get a big grin when I mention feedback, and they have to tell me their personal story about how they’ve reduced their energy use,’ says Armel.”

I continue to see Prius effect thinking in a range of projects—I fall into the same thinking myself: effective, attractive data served up to people is the key to driving better system performance.

No, it’s not.

Let me explain.

I don’t doubt that drivers of cars with energy information displays like the Prius can use the feedback to modify behavior. As a driver-owner of Honda Civic hybrid cars, I have used real-time mileage feedback to try to improve my energy performance while driving.

Here are a few reasons why the ca. 2009 Prius effect observed by Armel worked for people in her circle:

(1) The instantaneous mileage performance is available at all times with a glance at a gauge;

(2) The feedback signal in the early model Priuses was a bar graph that moved beside an indexed scale—higher is better, lower is worse, and it was easy to interpret.

(3) The main control lever in a car with automatic transmission is the accelerator; it’s easy to learn the connection between using the accelerator to reduce RPM and the mpg display.

(4) The Prius driver sits in the driver’s seat, interacting with accelerator and brake to change driving actions to improve performance.

(5) Prius drivers may be motivated by bragging rights and concern for the environment actually to drive conservatively, adjusting their driving actions, guided by their display.

Reasoning by analogy to the Prius effect, in the past 15 years people have designed many information interfaces to make energy use visible to building occupants and staff in order to drive action.

There are too many attractive displays, interactive dashboards, and web apps that fail to achieve real impact, which means changes to the system and improved performance.  I've built my share.

And the tools to develop interesting interactive displays are increasingly powerful and flexible, making it ever easier to create more dashboards, web apps, and feedback systems. Nonetheless, achieving changed behavior and improved performance remains the aim of all that information design work.

A bit more thinking has helped to clarify the connection between information displays and people acting to improve performance.

The five reasons I suggested for the Prius effect are specific instances of a more general set of factors. Once someone has defined a measure relevant to assessing performance and figured out a way to generate data for the measure, now what?

To use relevant data to improve performance, a person or group must

(1) sense the data;

(2) interpret the data;

(3) connect the interpretation to one or more suitable actions that will improve performance;

(4) have the power or potential to act, based on step (3) (“can do”);

(5) actually act to change system performance (“actually do”).

While there’s a lot of fun and challenge for people like me to develop relevant measures and data and then to craft inspiring and engaging ways to achieve steps (1) and (2), that’s all preliminary to the change and action steps (3) through (5).

In order to build more useful and engaging data displays that will contribute to better system performance, I've concluded that I need to pay more attention to how people will take steps (3) through (5) so my information designs actually contribute to better systems.