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Harish Jose


PDCA and the Roads to Rome

Can a lean purist and a Six Sigma purist reach the same answer to a problem?

Published: Tuesday, June 14, 2016 - 14:32

In this article I want to look at the concept of equifinality in relation to the plan-do-check-act (PDCA) cycle. In systems theory, equifinality is defined as reaching the same end, no matter what the starting point was. This is applicable only in an open system, one that interacts with its external environment. This could be in the form of information, material, or energy. I want to focus particularly on the repeatability of the PDCA cycle.

PDCA is the framework for the scientific method. If three different people, with different ways of thinking, are facing the same problem, can all three reach the same end goal using the PDCA process? This would imply that equifinality is possible—see the illustration below. Point A is the initial condition, and point B is the final desired condition. The three different colored lines depict the three different thinking styles. 

Iterative nature of PDCA

The most important point about PDCA is the iterative nature of the cycle. Each cycle of PDCA leads to a new cycle that is more refined, which allows the practitioner to learn from each step. The practitioner observes the effect of each step on the problem, and every action is an opportunity for further observation. The results of experiments lead to more experiments, and yield a better understanding of multiple cause-and-effect chains in the system.

If the scientific method is followed properly, it’s highly likely that the three different practitioners can ultimately reach the same destination. The number of iterations would vary from person to person due to different thinking styles. However, the iterative nature of the scientific method ensures that each step corrects itself based on the feedback. This type of steering mechanism based on feedback loops is the basis of the PDCA process, and the idea of multiple ways or methods to achieve the same final performance result is equifinality. This is akin to the saying “all roads lead to Rome.”

Final words

This post was inspired by the following thought: Can a lean purist and a Six Sigma purist reach the same final answer to a problem if they pursued the iterative nature of the scientific method? There has been a lot of discussion about which method is better. The solution, in my opinion, is in being open and learning from the feedback loops from the problem at hand.

I’ll finish this with a neat mathematical card trick that explains the idea of equifinality further. This trick is based on a principle called Kruskal Count.

The process
The spectator is asked to shuffle the deck of cards to his heart’s content. Once the spectator is convinced that the deck is thoroughly shuffled, the magician explains the rules. The Ace is counted as one, and all the face cards (Jack, Queen, and King) are counted as five. The number cards have the same values as the number on the card.

The spectator is asked to think of any number from one to 10. He is then directed to hold the cards face down, and then deal cards face up in a pile. He should deal the amount of cards equal to the number he chose in his mind. The spectator makes note of the value of the final card dealt, and is directed to deal those many cards face up on the already dealt cards.

This process is repeated until the spectator has reached a point at which point there aren’t enough cards to deal equal to the current card facing up in the pile. For example, the card is the eight of hearts, and there are only six cards remaining. The eight of hearts is the spectator’s selected card. He then puts the cards he has on his hands face up on the table, and places the other face-up cards on top. The spectator does this while you have your back turned. You easily find their selected card.

The secret
All roads lead to Rome. This trick has a more than 80-percent success rate.

The secret is to repeat exactly what the spectator did. You also choose a random number between one and 10, and start dealing as described above. Just like the concept of equifinality, no matter which number you chose as your starting position, as you go through the process, you will choose the same set of cards at the end, resulting in the same selected card! Try it for yourself. Here is a link to a good paper on this.

Always keep on learning...


About The Author

Harish Jose’s picture

Harish Jose

Harish Jose has more than seven years experience in the medical device field. He is a graduate of the University of Missouri-Rolla, where he obtained a master’s degree in manufacturing engineering and published two articles. Harish is an ASQ member with multiple ASQ certifications, including Quality Engineer, Six Sigma Black Belt, and Reliability Engineer. He is a subject-matter expert in lean, data science, database programming, and industrial experiments, and publishes frequently on his blog Harish’s Notebook.