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Checklists are powerful tools, proven to increase the accuracy of behavior and to reduce error, particularly slips and memory lapses. They are especially important in situations with multiple, complex requirements, and even more so where there are interruptions. With multiple people involved in a task, it is essential that the lines of responsibility be clearly spelled out. It is always better to have two people do checklists together as a team: one to read the instruction, the other to execute it. If, instead, a single person executes the checklist and then, later, a second person checks the items, the results are not as robust. The person following the checklist, feeling confident that any errors would be caught, might do the steps too quickly. But the same bias affects the checker. Confident in the ability of the first person, the checker often does a quick, less than thorough job.

One paradox of groups is that quite often, adding more people to check a task makes it less likely that it will be done right. Why? Well, if you were responsible for checking the correct readings on a row of fifty gauges and displays, but you know that two people before you had checked them and that one or two people who come after you will check your work, you might relax, thinking that you don’t have to be extra careful. After all, with so many people looking, it would be impossible for a problem to exist without detection. But if everyone thinks the same way, adding more checks can actually increase the chance of error. A collaboratively followed checklist is an effective way to counteract these natural human tendencies.

In commercial aviation, collaboratively followed checklists are widely accepted as essential tools for safety. The checklist is done by two people, usually the two pilots of the airplane (the captain and first officer). In aviation, checklists have proven their worth and are now required in all US commercial flights. But despite the strong evidence confirming their usefulness, many industries still fiercely resist them. It makes people feel that their competence is being questioned. Moreover, when two people are involved, a junior person (in aviation, the first officer) is being asked to watch over the action of the senior person. This is a strong violation of the lines of authority in many cultures.

Physicians and other medical professionals have strongly resisted the use of checklists. It is seen as an insult to their professional competence. “Other people might need checklists,” they complain, “but not me.” Too bad. Too err is human: we all are subject to slips and mistakes when under stress, or under time or social pressure, or after being subjected to multiple interruptions, each essential in its own right. It is not a threat to professional competence to be human. Legitimate criticisms of particular checklists are used as an indictment against the concept of checklists. Fortunately, checklists are slowly starting to gain acceptance in medical situations. When senior personnel insist on the use of checklists, it actually enhances their authority and professional status. It took decades for checklists to be accepted in commercial aviation: let us hope that medicine and other professions will change more rapidly.

Excerpted from ‘The Design of Everyday Things’ by Don Norman