PDCA Cycle or PDSA Cycle – Which is Right?

Review of: PDCA Cycle Training
Lean Manufacturing:
Pete Abilla

Reviewed by:
On May 12, 2014
Last modified:May 12, 2014


PDCA Cycle for Improvement is a great methodology used by Toyota to improve operations.

There’s quite a bit of confusion between the use PDCA Cycle versus PDSA Cycle. For those unfamiliar with the acronym, PDCA stands for Plan-Do-Check-Act and PDSA stands for Plan-Do-Study-Act. To some, the change of “check” to “study” might be trivial, but to Dr. Deming and his teacher, Dr. Walter Shewhart, there is a difference between “check” and “study”.

The PDCA or PDSA Cycle began as a series of steps within the world of product development. It wasn’t until much later did it become a method for process improvement. Let’s go through the history together.

1. The Shewhart Cycle

Dr. Walter Shewhart is best known for his development of statistical control. Back in 1939, Dr. Shewhart struggled with the current view of his time regarding quality and product development. He didn’t believe it was a linear model, but rather a cycle. In his words,

These three steps must go in a circle instead of in a straight line, as shown . . . It may be helpful to think of the three steps in the mass production process as steps in the scientific method. In this sense, specification, production, and inspection correspond respectively to making a hypothesis, carrying out an experiment, and testing the hypothesis. The three steps constitute a dynamic scientific process of acquiring knowledge. 1

In his mind, it looked like this:

shewhart cycle diagram

2. The Deming Wheel

Dr. Walter Shewhart’s student at the time was Dr. W. Edwards Deming. It was Deming who took the Shewhart Cycle and modified it. In 1950, while speaking to the Japanese Union of Scientists and Engineers (JUSE) regarding statistical quality control, Dr. Deming modified the Shewhart Cycle by adding a 4th step that he called – at the time – “redesign through marketing research”. Historians believe that it was at that meeting the term “Deming Wheel” was born 2.

deming wheel image in pdsa

At that meeting, Dr. W. Edwards Deming discussed these steps:

  1. Design the product
  2. Make it and test in lab and production line
  3. Launch the product
  4. Test it in service via market research and user interviews
  5. Redesign and improve the product given customer’s feedback

3. PDCA Cycle is Born

According to Misaki Imai, Japanese executives took the Deming Wheel from that 1950 seminar and called it PDCA and took Deming’s steps (1-4) and codified it as Plan-Do-Check-Act 3.

pdca cycle from misaki imai

According to Imai, in the 1960′s, the what was initially the Deming Wheel was called PDCA by the Japanese. It evolved from a method to describe product development to become a method for process improvement.

4. PDSA Cycle is Reborn

In 1986, Dr. W. Edwards Deming reintroduces the Shewhart Cycle and warned his audience that Plan-Do-Check-Act (PDCA) version is not accurate because the English definition for “check” means to “hold back”. Deming continues by encouraging his audience to use Plan-Do-Study-Act (PDSA) and not the “corruption PDCA” 4.

5. PDCA or PDSA?

I’m not picking sides. I’ve always used PDCA. In fact, at Toyota PDCA is the recognized and approved framework, not PDSA. I’m not sure if that matters. I think in the grand scheme of things, in practice it really doesn’t matter. But, to theoreticians and academics, they will likely continue to quibble over PDCA versus PDSA. But for practitioners like you and me, we’ll be busy making things better.

What’s your opinion? Does it matter to you? 5

  1. Shewhart, W. A. 1939. Statistical Method from the Viewpoint of Quality Control. Department of Agriculture. Dover, 1986, page 45
  2. Deming, W.E. 1950. Elementary Principles of the Statistical Control of Quality, JUSE
  3. Imai, M. 1986. Kaizen: The Key to Japan’s Competitive Success. New York: Random House, page 60
  4. Deming, W.E. Personal letter to Ron Moen on November 17, 1990.
  5. Some parts of this article was taken from “Evolution of the PDCA Cycle” by Ronald Moen and Clifford Norman
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  1. Ondiappan Arivazhagan "Ari" says

    I does matter. I go with PDCA.

    Opinion #1:
    However in the above explanation, why 5 steps are needed to explain a 4-step CI cycle.
    IMO, the step# “3.Launch the product” is redundant, hence waste (NVA), and can be removed or can be merged with step #4.

    Opinion #2:
    It looks like, from the above points, that the real owners of the “PDCA cycle” is the set of unknown Japanese engineers, not Deming. Is it correct.?

    Opinion #3:
    Deming should have explained how the word “Study” is superior to the word “Check” in this context and In 1986, the did “study” not mean “examine” also. BTW, the word “Check” also means ” examine (something) in order to determine its accuracy, quality, or condition, or to detect the presence of something”.

    I am comfortable with PDCA and Deming was known for his clarity of thought and, I am afraid, not for such confusing remarks on trivial matters.


  2. Attila Hujak says

    If the “check” is used in general terms and the whole cycle is not just about the product development cycle, the “CHECK” can mean anything that is necessary to do after doing something to evaluate the outcome of the “DO” ! And the main message of the PDCA/PDSA is, not let the loop open! Semantic exercises on the wording could corrupt this great philosophy and approach itself!

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