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:
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.
At that meeting, Dr. W. Edwards Deming discussed these steps:
- Design the product
- Make it and test in lab and production line
- Launch the product
- Test it in service via market research and user interviews
- 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.
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
- Shewhart, W. A. 1939. Statistical Method from the Viewpoint of Quality Control. Department of Agriculture. Dover, 1986, page 45 ↩
- Deming, W.E. 1950. Elementary Principles of the Statistical Control of Quality, JUSE ↩
- Imai, M. 1986. Kaizen: The Key to Japan’s Competitive Success. New York: Random House, page 60 ↩
- Deming, W.E. Personal letter to Ron Moen on November 17, 1990. ↩
- Some parts of this article was taken from “Evolution of the PDCA Cycle” by Ronald Moen and Clifford Norman ↩