Expect Error

Expect Error

Humans make mistakes. A well-designed system expects its users to err and is as forgiving as possible. Some examples from the world of real design illustrate this point.

• For decades in the Paris subway system, Le Métro, users would buy a packet of small tickets that were inserted into a machine that read the ticket, printed a record on it that rendered it used, and then spit it out from the top of the machine. (The authors also describe local riders using an electronic card waved at a sensor.) The tickets had a magnetic strip on one side but were otherwise symmetrical. On Thaler’s first attempt to navigate the Métro, he was not sure how to use the system, so he tried putting the card in with the magnetic strip faceup and was pleased to discover that it worked. He was careful thereafter always to insert the card with the strip faceup. Many years and trips to Paris later, Thaler was proudly demonstrating to visiting friends the correct way to use the Métro system when his wife started laughing. It turns out that it didn’t matter which way you put the ticket into the machine! The only reason Thaler never made a mistake was that it was impossible to do so.

The authors contrast this with card readers they encountered in Chicago parking garages. When entering the garage, you put your credit card into a machine that reads it and remembers you. Then, when leaving, you must insert the card again into a machine at the exit. This requires reaching out of the car window and inserting the card into a slot. Because credit cards are not symmetrical, there are four possible ways to put the card into the slot (faceup or facedown, strip on the right or left). Exactly one of those ways is the right way. And in spite of a diagram above the slot, it is very easy to put the card in the wrong way, and when the card is spit back out but the gate does not go up, it is not immediately obvious what caused the card to be rejected or to recall which way it was inserted the first time. Both of us have been stuck for several painful minutes behind some idiot who was having trouble with this machine, and we both have to admit to having occasionally been the idiot who makes all the people behind him start honking.

• Over the years, automobiles have become much friendlier to their Human operators. In fact they are full of nudges. If you do not buckle your seat belt, you are buzzed. If you are about to run out of gas, a warning sign appears and you might be beeped. If you wander into another lane, your car makes an unpleasant sound. If you back up and are close to hitting something, you hear a loud warning. If you drive for three hours or more without stopping, your car might ask you if you would like to stop for a cup of coffee. Any remotely sensible car comes with an automatic switch for the headlights that turns them on when you are operating the car and off when you are not, eliminating the possibility of leaving your lights on overnight and draining the battery. Nudges of these kinds are saving lives, and we can expect many more of them in the future.

But some error-forgiving innovations are surprisingly slow to be adopted. Take the case of the gas tank cap. A plastic tether keeps a removed gas cap attached to the car, so it cannot be left behind at the pump. Our guess is that this bit of plastic cannot cost more than 10 cents. Once some carmaker had the good idea to include this feature, what excuse can there ever have been for building a car without one?

Leaving the gas cap behind is a special kind of mistake psychologists call a “postcompletion” error.7 The idea is that when you have finished your main task, you tend to forget things relating to previous steps. Other examples include leaving your ATM card in the machine after getting your cash or leaving the original in the photocopier after getting your copies. Most ATMs (but still not all!) no longer allow this error because you get your card back immediately. Another strategy, suggested by Don Norman, is to use what he calls a “forcing function,” meaning that in order to get what you want, you have to do something else first. So if you have to remove the card in order to get your cash, you will not forget to do so. Unless, of course, you forget why you came to the ATM.

• Another automobile-related bit of good design involves the nozzles for different varieties of gasoline. The nozzles that deliver diesel fuel are too large to fit into the opening on cars that use gasoline, so it is not possible to make the mistake of putting diesel fuel in your gasoline-powered car (though it is still possible to make the opposite mistake). The same principle has been used to reduce the number of errors involving anesthesia. One study found that human error (rather than equipment failure) caused 82 percent of “critical incidents.”8 A common error was that the hose for one drug was hooked up to the wrong delivery port, so the patient received the wrong drug. This problem was solved by designing the equipment so that the connectors were different for each drug. It became physically impossible to make this previously frequent mistake.
• A major problem in health care is medication adherence and drug compliance. Many patients are on medicines they must take regularly and in the correct dosage. The book cites an estimate of more than 125,000 annual deaths in the United States associated with not taking prescribed medicines.9 In principle, all of those deaths ought to be preventable. Nudges should be able to help, which brings us to an interesting choice-architecture question: If you are designing a drug and you have complete flexibility, how often would you want your patients to have to take their medicine?

If we rule out a onetime dose administered immediately by the doctor (which avoids the need to remember later doses but is often technically infeasible), the authors consider how a recurring routine can help people remember a dose, where the medicine permits that schedule. A suitable schedule with fewer daily doses creates fewer occasions for forgetting. But frequency is not the only concern; regularity is also important. A daily dose can be easier to connect to a routine than an alternate-day dose; the appropriate schedule depends on the medicine. An established routine may help people remember a medicine, though adding another pill can also make a regimen harder to manage. (Pill container boxes, one for each day, are useful nudges.) An alternate-day schedule can be harder to remember. (Similarly, meetings that occur every week are easier to remember than those that occur every other week.) Some medicines are taken once a week, and many patients take such medicines on Sundays (because that day is different from other days for most people and thus easy to associate with taking one’s medicine). Take the pill before going to church, turning on the game, doing the puzzle, or what have you.

Some birth control regimens illustrate this problem: active pills are taken every day for three weeks, followed by one week without active pills. To solve this problem and to make the process automatic, the pills are sold in a special container that contains twenty-eight pills, each in a numbered compartment. Patients are instructed to take a pill every day, in order. The pills for days twenty-two through twenty-eight are placebos whose only role is to facilitate compliance for Human users. There is room for a lot more thinking about effective nudges to promote medication adherence; they could save numerous lives.10

• While working on the first edition of this book, Thaler sent an email to his economist friend Hal Varian, who works for Google. Thaler intended to attach a draft of the introduction to give Hal a sense of what the book was about, but he forgot the attachment. When Hal wrote back to ask for the missing attachment, he noted with pride that Google was experimenting with a new feature of its email program, Gmail, that would solve this problem. A user who mentions the word attachment but does not include one would be prompted: “Did you forget your attachment?” Thaler sent the attachment along and told Hal that this was exactly what the book was about.

Google caught on and now has an assortment of nudges specifically designed to address forgetfulness. As the company put it in 2018, “When your inbox is flooded with emails, some will inevitably slip through the cracks. Luckily, the new Gmail can help. It will now ‘nudge’ users to reply to emails they may have missed and to follow up on emails for which they haven’t received a response.”11 As both of us have found, the feature is useful. With respect to an email sent to Sunstein about one of his writing commitments, for example, the program said, “Sent 6 days ago. Follow up?” To its credit, Google practices libertarian paternalism. The company adds: “Nudging is on by default for users with the new Gmail enabled, but they can turn it off from their Gmail settings menu if they choose.” Hurray!

• Visitors to London who come from the United States or other parts of Europe have a problem being safe pedestrians. They have spent their entire lives expecting cars to come at them from the left when they cross the street, and their Automatic System knows to look that way. But in the United Kingdom, automobiles drive on the left-hand side of the road, so the danger often comes from the right. Many pedestrian accidents occur as a result. The city of London tries to help with good design. On many corners, especially in neighborhoods frequented by tourists, the pavement has signs that say, “Look right!” After the initial publication of this book, Thaler became a frequent visitor to London and was always grateful to those signs for preventing unhappy collisions with oncoming traffic.