Home > Improvement Kata & Coaching Kata> RETIRE THE PDCA WEDGE?


Thank you LEI for letting us share ideas & findings. Some things we in the Lean community have learned to believe may not actually be true. For our first posting we invite you to take a look -- and think about -- this discussion starter.
By Mike Rother and Jeff Uitenbroek | May 2012
by Joseph Kinsella | June 2012
This is a great article.
The thing that you are describing with the wedge is the difference between the Eastern and the Western way of doing things. It is a mind set thing.
One of the trainers that taught me Lean said to me. We are told to teach you the 5S system. The last S being (Sustain) but in Toyota we call it the 4S system. The reason being once we have done all of the hard work to sort out the Visual Factory we at Toyota expect people to keep up the improvement. We do not say " Can you now keep up the improvments " It is a Western way to allow slippage.

In the West companies have made their money to easily.

In the East people learn the Martial Arts and in that system if you slip back you will die. Only the best survive in deadly combat. This way of thinking carries over into their current working lives.

Many thanks for this PURE thought.

Have a nice day. Feedback is the breakfast of champions.       
by Herbert Gensch | June 2012
Interesting thoughts and concepts; thanks for stimulating my brain to a deeper level of thinking!

The goal is always to "keep the ball rolling"; a concept you explained well.

If standards are not a wedge and the process decays; it is because we have allowed the standard to erode.  Maybe science erodes the wedge if the ball does not move (friction, force, decomposition, etc.).

I believe the true course is not to allow the ball to spin in place, but drive it upward towards the goal!

Thanks again for the challenge.

by Tim Mann | June 2012

I think the images of a wedge as a standard and the wheel as PDCA’s are incongruent.  A different picture needs to be developed to explain the relationship between striving to reduce process variability and process standardization (knowing the new best practice), and between following standards and improvising (entropy).

I propose a mouse in a maze.  The maze is the process and the walls are the standard.  A PDCA is an experiment where a wall in the maze is moved to a different position to try and enable the mouse to get through the maze easier or quicker.  The mouse may choose to go through the maze at a slower pace or even climb over a wall to follow a different path (entropy or adverse to change).  For a physical process, entropy is some of the walls becoming shorter over time, allowing variations in the path.
Tim - Thetford Corp.

by F K | June 2012

After trying for 15 years now to understand why people are motivated and how to stimulate this motivation, I maintain the following observations and antitheses. You wanted a feedback? Here you are!


Slide 2 +3: Here are mixed terms. What should be the message here? Bring the terms such as lack of discipline and entropy together, I think is inappropriate. They cannot hit a problem. The one is physics and the other social psychology. It is a fact that entropy always increases - even with improvements! Even though I am improving, increases the entropy. It always rises. There is no process on earth where it does not rise. The idea that you can avoid the increase of entropy is thermodynamic nonsense. It is also true: Processes deteriorate if people are undisciplined. Why people are undisciplined? Simple: because life is not just about discipline.

Slide 4: The idea that you can stay with a permanent improvement in the regression is like the idea of eternal life. And so it is only in religion.

 Slide 5: No one wants to continuous improvement / change - this is to always claim social, neurobiological and ethical nonsense.

Slide 6: Toyota is in danger to be glorified. As socially and sensitive as this company is always shown, it is not. If it culture were so simple and social connectable, why there is no more of these cultures? Because this culture limits the right of self-determination. Part of the crisis of Toyota was certainly the fact that the new generation of Toyota don’t integrate themselves so easy in the company anymore compared to the older generation who built the culture. If someone does not comply with the standard of Toyota, then he is punished by the social group – I asked people who work there. Autonomous personalities would never want to work at Toyota.

Slide 7: No one ever said that standards should replace or interfere with scientific thinking; - this is a rhetorical statement / question.

Slide 8: I do not understand why the concept of entropy is used.

Slide 9: As I said, there is no process on earth, where entropy is not increasing. Why the sense of the word standard is now being redefined? A standard is a standard and a goal is a goal. Standards are not goals.

Slide 10: This adage applies to the molecular level. PANTA REI only applies at the micro level, but not in a social-psychological system - see the slide 5. Please, we distinguish two types of change: from the outside and inside. People like standards - if they have it imposed them by themselves - not if they are externally defined. Both views should be distinguished. We are not all “equipped” to learn throughout life – even if many teachers would like to see this. Take a look at our schools. Not everyone can make it in the world. To personality development, a sense of coherence is necessary, which doesn’t come by itself or through external training.

Slide 11: What should the message be? DEMING was wrong? In my view it's not good if you attributing statements to already deceased people. Motivation cannot be carried out through routines. No one can train others to be motivated. To provide sense and motivation by external circumstances – coaching - is impossible. Ask a neurobiologists and psychologists. Even under threat of life-time great thinkers have not changed their attitudes, but died for their visions. The pursuit of a goal does not motivate. The converse is true for the launch: Only if Motivation is present, a goal is sought.


What annoys me is that new terms must always be used to draw attention to the authors. Let's take the word kata in the strictest sense. It comes from the martial arts. It is a routine. A routine what someone has adapted. He makes moves that would make no one else volunteered. And why? What is the driver for him? Money? No, there are the two basic human needs: growth and belonging to a group. People experience themselves as growing and belonging, and then they do something. I think Toyota is wildly inflated. Why do the people at Toyota give up freely their self-determination? It must be a wonderful world for growing personalities. I just don’t believe it, sorry.


I look forward to feedback.



by Ramesh P R | May 2012
by Jason Schulist | May 2012

Improvement Kata seems like a lever to drive PDCA forward and the target condition seems like a magnet or a "channel" for focusing the PDCA.

by Jason Schulist | May 2012
When I look at page 9 _ A standard is a target condition, I don't see the target condition as a wedge - It is more like a magnet that assists the experimentation and the PDCA cycle versus a more difficult slope to traverse.

by Jay Bitsack | May 2012
Just as a quick afterthought to my prior post.  If a "kata" is a behavior that needs to or should be praticed, then it seems possible to view the PDCA wedge as a "kata" block (as opposed to a "chock" block) that prevents the CI wheel from rolling backward.
by Jay Bitsack | May 2012

Hi Mike and Jeff:

You've asked a thought provoking question and posited an interesting way of looking at the role of standards/standardization in the continuous improvement cycle.  Based on how you presented your argument, what you're suggesting as new location for the "wedge" makes good sense.


If, however, one was to view the PDCA cycle as being akin to the scientific method and the wedge as being a proen theory - as opposed to a hypothesis, then the wedge in its traditional location makes sense.  It functions as the latest accepted/proven body of knowledge that exists regarding how and why a particular observed system works.  If one wishes to test the system and reproduce the theoretical results, one must be able to faithfully duplicate the conditions under which the theoory holds.  In the case of any standardized process, the capability of that process to operate at a desired or target level of performance is only theoretically possible.  Any varables that can act on that system must be held in control in order for it to realize its currently known or proven potential.  Ergo, the theory actually serves as a mechanism for holdign the current system in place, with the potential variables beinig held withinin a relatively static band of variability.


In order for a new and better theory to be developed, tested, and proven, the PDCA cycle has to be put into motion... ideally with a pulling force.  I see that pulling force being akin to a hypothesis or an idea/concept for how a particular process might be made to perform at a greater capability level (i.e., less waste, more efficiency).  The hypothesis then serves as a new set of conditions/parameters under which the system can be tested to determine whether or not the new conditions actually result in improved performance.  If so, and those conditions can be faithfully reproduced by others on a consistent basis - achieving the same desired results, then the hyposthesis become the new accepted theory.  And it will remain as such until disproven.

The perspective I've just described may be driven primarily on a semantic basis, but I tend naturally tend to subscribe to a higher level of precision in the meaning and use of words in English language.  Hopefully, that's in keeping with the principles of lean thinking and the teachings of Taiichi Ohno, et al.  So, bottom line... the wedge is useful as a reminder of the conditions required to keep the continuous improvement cycle from backsliding.  However, creative/innovative thinking or problem-solving and an attitude of never being satisfied with the status quo might be added to the diagram as an engine that powers the PCCA wheel.

Best regards, Jay

by Peter Alfvin | May 2012

Thanks for writing this.  The distinction between "standard" and "standardized work" as always fascinated me.

Do you know when, where and by whom the "wedge" concept was introduced into the Lean literature?


Kata Contributors
Gerardo Aulinger
Barb Bouche
Elizabeth Carrington
William Costantino
Jeremiah Davis
Tyler Fife
Richard Fleming
Håkan Forss
Dennis Gawlik
Richard Green
Craig Kennedy
Jeffrey Liker
Drew Locher
Michael Lombard
Constantin May
Kyle Muramatsu
Tyson Ortiz
Stuart Powell
Tadas Puksta
Nicole Purrier
Mark Rosenthal
Mike Rother
Meryl Runion
Tilo Schwarz
Karsten Seydel
Julie Simmons
Alex Thomason
Jeffrey Uitenbroek
Emiel van Est
Tony Webster
Todd Weston