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January 12, 2020

"Mistake-Proofing: Designing Errors Out"


I spent a most instructive half-hour earlier this afternoon with this slim (72 pages) book.

You know how I feel about mistakes: it's so much easier to avoid them than to correct them.

Especially if they're links in a chain of events that go off the rails as a result.

The book was originally published in hardcover by Productivity Press in 1995.

As of January 2002, it had been out of print for several years.

The rights reverted back to the authors, who made it available as a print-on-demand title.

Below, excerpts.

Mistake-Proofing: Designing Errors Out

This book is about mistakes and how to prevent them from ruining your business. It's about how to rescind Murphy's Law. In this book we present a way in which you can control the mistakes that cause the defects. It allows you to go back into the process, weed out the mistakes, and ensure that they will never be a problem again. We call this mistake-proofing.

Mistake-proofing is really quality control in its strictest sense. It does not redesign a process as reengineering does, nor does it track problems as statistical process control does. It simply keeps the system performing as it was originally designed to perform.

As a method, mistake-proofing is comprehensive. You can apply it to services just as easily as to manufacturing. This is because mistake-proofing is designed to deal with defects that originate from human mistakes as well as those that originate from equipment and materials.

Most importantly, mistake-proofing is the only method we know that includes customers' actions in the quality control system. The importance of this is emphasized by one study that estimates that customers of services are responsible for one-third of the the problems they complain about.

Another big advantage of mistake-proofing is that it is simple — you don't need a Ph.D. in statistics to apply it. In reality, mistake-proofing is more like a structured form of common sense.

Mistake-proofing is also inexpensive relative to its design alternative, redundancy.

Mistake-proofing works on the principle that if you look behind every defect, you will find a mistake that caused it. For our purposes, we define a mistake as the result of an activity, either mental or physical, that deviates from what was intended. If you can correct or prevent the mistakes in your business, you will eliminate the defects.

Machine mistakes, being generally mechanical in nature, are better understand than human mistakes. They are, therefore, more predictable and easier to control. If we look closely at the different types of machine mistakes, we see that they fall into two categories: those mistakes we can see coming and those that catch us unaware.

Employees experience a continuous stream of encounters — one defect is a low failure rate. Customers experience a single defect as a 100% failure rate.

Mistakes are random events and therefore we must continuously watch for them. Sampling is not good enough. It looks at only a small proportion of the outputs in a process. It assumes that the rest of the outputs will be similar to the sample and that, therefore, we can draw conclusions about the entire output.

The best way to ensure the detection of a mistake is to make sure that something in the environment makes it very obvious that one has been made. A good example of an environmental cue is the inevitable "extra" parts that remain after a do-it-yourself repair project. These parts make it very clear that you have not reassembled the item correctly.

The key to creating mistake-proofing devices and procedures is not to do too much at once. Instead, concentrate on clever, inexpensive methods to check for only one mistake at a time. If you have two possible mistakes, develop two separate devices or procedures to catch them.

Toyota, which is very experienced at mistake-proofing, averages about twelve devices for each machine.

Go/No-Go gauges are not limited to the shop floor. Customers often use such gauges to detect and prevent mistakes. Some amusement park rides require riders to be above a certain height (so they do not slip through the safety restraints) or below a certain height (to keep larger people off of rides meant only for small children). Parks do not want customers to discover they are too small or large after waiting in a potentially very long line. By placing a gauge at he front of the line, customers can tell if they are tall enough (or short enough) to go on the ride without waiting in line.

Remember that the goal is to develop clever, simple and inexpensive devices. Don't immediately opt for the high-tech solution.

Preview the book here.

Note: If I'd taken the road not taken and continued in academic anesthesia, eventually chairing a department, I'd have bought as many copies of this book as there were members of my department — faculty, residents, nurse anesthetists, medical students.

Then I'd hand each person a copy as they entered weekly rounds.

The first half hour of these "Time-Out" rounds would be silent, with everyone present asked to focus on their new book.

The final half hour would be a directed free-for-all, with me leading a discussion that made its way through the book front-to-back.

What's the cost of one-brain dead patient avoided?



January 12, 2020 at 04:01 PM | Permalink


But see "No Good Deed Goes Unpunished: Case studies of incidents and potential incidents caused by protective systems"


Systems to identify or prevent mistakes, if not considered properly, can increase risk or magnify harm. Tim Harford discusses in an episode of his podcast:


Posted by: strunkl | Jan 13, 2020 2:42:57 PM

Joe, Perhaps you will find this book to your taste:

When I bought it in hardcover many moons ago, the title was The Psychology of Everyday Things. It is an explication of application psychology. Note: application psychology, not applied psychology.

In short, there is knowledge in the head and knowledge in the world. The best designs put knowledge in the world. The best example is now extinct: the microfloppy disc. It was designed so that it would fit the drive only one way. And you could drop it in a shirt pocket.

It was worth my time and then some. Perhaps it will be worth yours.

Posted by: antares | Jan 13, 2020 7:48:38 AM

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