In Lean Six Sigma and Six Sigma, poka-yoke (poh-kah yoh-keh) is a tool used to identify steps in a process where an error is likely to occur. This allows companies to make changes to avoid mistakes before operations even begin. It’s a simple but powerful tool that applies to any operation in any industry.

Also known as error-proofing or mistake-proofing, poka-yoke is considered a key item in the Six Sigma toolbox. Project teams use poka-yoke in Lean, which focuses on eliminating waste, as well as Six Sigma, which focuses on eliminating defects.

In both cases, the final goal is the same: finding and eliminating potential problems in a process before they happen, or correcting mistakes in an existing operation.

How Poka-Yoke Began

Toyota engineer Shigeo Shingo coined the term poka-yoke in Japan in the 1960s. Shingo ranks among the greatest pioneers in continuous process improvement and operational excellence. His many achievements include developing the concept of the Single-Minute Exchange of Die and using poka-yoke techniques to both correct and prevent defects.

Poka-yoke focuses on solutions that permanently correct an ongoing or expected issue, not just fixing a problem for one instance. It remains part of the Toyota Production System (TPS) as a feature in Jidoka, which allows workers or automated machinery to stop a process if they detect the potential for a defect or mistake.

How Poka-Yoke Works

Poka-yoke can work in both a proactive and reactive way. It’s most useful when used to ensure that the optimum conditions exist before a process begins, preventing mistakes from happening. However, if defects are already detected, poka-yoke techniques can identify errors and give teams a chance to quickly eliminate them.

Putting poka-yoke to work involves following a series of steps. They typically flow as follows, according to the American Society for Quality (ASQ). This is an example of proactively using poka-yoke.

  • Create a detailed process flow chart of every operation in a process, no matter how small.
  • Review each step to determine where human errors are likely to occur – this can involve the 5 Whys.
  • Once every potential error is found, work through the process to find the root cause.
  • Design solutions in the process to eliminate the risk of the error ever happening. This can include eliminating the step or replacing it with a mistake-proof step.
  • If the team cannot eliminate the step that involves the potential error, they can come up with ideas to minimize its impact should an error occur. This can include establishing inspection methods or setting strong parameters on the functions of a step so that errors are easily detected.

To get rapid feedback on potential errors once an operation starts, three types of inspection methods work best. A successive inspection calls for the next worker in the process to inspect the work done before her. Self-inspection involves employees checking their own work as soon as they have it completed. A source inspection involves a check before that step in the process begins to ensure the optimum conditions exist (automated systems often handle this issue).

Examples of Poka-Yoke

Simple examples of poka-yoke are apparent in everyday life.

  • If you frequently are late leaving the house in the morning because you can’t find your car keys, find the optimum place to put them each night so you know where they are in the morning.
  • On cars with a start button, drivers must first press the brake, preventing unwanted and potentially dangerous movement of the vehicle.
  • Many child-proof mechanisms represent the principles of poka-yoke, finding key areas where accidents can occur and taking steps to reduce the risk of them happening.

In business, the idea of poka-yoke is apparent in many activities, especially in the online world. Online forms prevent omissions and errors by not allowing people to hit the “submit” button until every field is properly filled out. Many online forms require filling out email addresses twice to assure they are correct (people take this same mistake-proofing step when setting a new password).

It also works with complex challenges, such as the check-in procedures at a hospital or how restaurants greet and seat patrons during busy times of the day. In both cases, poka-yoke can make the process more efficient by finding the points in the process where errors will likely occur (or are already occurring).

Why Poka-Yoke Is Important

Even the smallest error in a process can cause large problems down the road. For most businesses, they will impact the bottom line and the ability to fulfill customer requests. There’s also a loss of professionalism when a company does not correct an easily avoidable error.

The universal nature of poka-yoke also makes it valuable. It can help detect issues in any operation where mistakes can occur (which is basically every type of operation). Poka-yoke can help solve problems with processing, set up, missing or inadequate equipment and parts, measurement errors, human operation mistakes and much more.

Learning how to put poka-yoke into action is part of earning a Lean Six Sigma or Six Sigma belt certification. It’s considered one of the keys of process improvement methodology and something students learn early in their Lean Six Sigma careers.