Poka Yoke Corner

“Mistake proofing is the use of process or design features  to prevent errors or the negative impact of errors.” (Shingo, 1986).

Mistakeproofing is also know as “poka yoke”, a Japanese slang for avoiding errors. Mistakeproofing is used where human error can cause mistakes or defects to occur especially in the processes relying on workers’ skills, attention and experience.

To err is human!

Shingo (1986) makes a clear distinction between a mistake and a defect. Mistakes are inevitable and human error is unavoidable when people are not very concentrated on understanding the instructions that they are given. Defects are the results of mistakes and entirely avoidable.

There is no comprehensive typology of mistake-proofing. The approaches to error reduction are diverse and evolving. More innovative approaches will evolve, and more categories will follow as more organizations and individuals think carefully about mistake-proofing their processes. Tsuda (1993) lists four approaches to mistake-proofing:

  1. Mistake prevention in the work environment.
  2. Mistake detection (Shingo’s informative inspection).
  3. Mistake prevention (Shingo’s source inspection).
  4. Preventing the influence of mistakes.

The main purpose of mistakeproofing is to eliminate human errors. Therefore, human error deserves special emphasis. Rasmussen (1997) and Reason (2000) define three types of errors based on how the brain control actions.

  • Skill-based actions.
  • Rule-based actions.
  • Knowledge-based actions.

Berwick (2001) states “…We are human and humans err. Despite outrage, despite grief, despite experience, despite our best efforts, despite our deepest wishes, we are born fallible and will remain so. Being careful helps, but it brings us nowhere near perfection… The remedy is in changing systems of work. The remedy is in design. The goal should be extreme safety. I believe we should be as safe in our hospitals as we are in our homes. But we cannot reach that goal through exhortation, censure, outrage, and shame. We can reach it only by commitment to change, so that normal, human errors can be made irrelevant to outcome, continually found, and skillfully mitigated.”

It is possible to come across with several mistakeproofing examples used in different trades. Below is an example of color coding. The aim is to prevent errors by distinguishing the wire-nuts depending on the colors.

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Below is an example of mistakeproofing in the industry providing that there is a signalling system when there are missing bolts.

poka-yoke-in-industry

<More examples to be provided> 

Mistakeproofing examples might be categorised depending on the type and function that they have.

References

Berwick, D. (2001). Not again-Preventing errors lies in redesign-not exhortation. British Medical Journal, 322, 247-248.

Rasmussen, J. (1997). Risk management in a dynamic society: a modelling problem. Safety Science, 27, 183-213.

Reason, J. (2000). Human error: models and management. British Medical Journal, 320, 768-770.

Shingo, S (1986). Zero quality control: source inspection and the poka-yoke system. trans. by Dillion AP. New York: Productivity Press.

Tsuda, Y. (1993). Implications of foolproofing in the manufacturing process. In: Quality through engineering design. Kuo W, ed. New York: Elsevier.