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PDCA Cycle: Continuous Improvement with Shewhart and Deming

PDCA Cycle

PDCA CycleThere aren’t many ideas so big that we use them every day – often without thinking. But the PDCA Cycle, Plan-Do-Check-Act, is one.

The PDCA Cycle comes with many names and none. It’s pretty much something humans have been doing since the dawn of time. But that doesn’t diminish the idea.

So, what is the PDCA Cycle, and how has it evolved?

What is the PDCA Cycle?

The PDCA Cycle as we use it today is the creation of the great management thinker W Edwards Deming. It is an iterative model for continuous improvement. Therefore, you’ll find it at the heart of quality methodologies like Kaizen, Total Quality Management (TQM), and Six Sigma.

The acronym stands for the four steps in the cycle, which repeat until you reach a stable working product, or the solution to your problem. Although, in Kaizen, since we are after continuous improvement, the cycle never stops.

The four steps are:

  1. Plan
  2. Do
  3. Check
  4. Act

We’ll look at the steps in detail later.

The Origins of The PDCA Cycle

Although it was W Edwards Deming who introduced the PDCA Cycle, he attributed it to Walter Shewhart. In the 1920s, Shewhart articulated a simple product process, that he based on the scientific method:

  • Specification
  • Production
  • Inspection

He later simplified and generalised this to:

  • Plan
  • Do
  • See

Which gives us the more common modern terminology of the ‘Plan-Do-Review cycle’.

The Scientific Method

In this, we can readily see the echoes of  the scientific method:

  • Hypothesis
  • Experiment
  • Analysis

To Japan…

Along with the other great American prophet of Quality, Joseph Juran, Deming went to Japan after the Second World War. There, he consulted with Japanese manufacturing industry, and propounded the PDCA Cycle, that was also known then as the ‘Deming Cycle’, or the ‘Deming Wheel’.

Deming himself preferred to refer to it as the ‘Shewhart Cycle’. So many names!

There, not surprisingly, companies like Toyota took up his ideas eagerly and incorporated the PDCA Cycle into the Toyota Production System and Lean Manufacturing.

From PDCA to PDSA Cycle

Later in his life, in the mid-1980s, Deming shifted his terminology from PDCA Cycle to PDSA Cycle:

  • Plan
  • Do
  • Study
  • Act

He preferred the emphasis on analysis that the word ‘study’ conveys, to the more passive inspection that ‘check’ implies. In this way, he was further reverting to the roots of the approach in the scientific method.

The OODA Loop – a Kindred Concept

I would recommend that you also read our article on Colonel John Boyd’s OODA Loop. This idea is in many ways similar to the PDCA Cycle. But it offers additional insights that will help you refine your understanding and practice.

So, it’s time to dissect the PDCA Cycle…

The Steps of the PDCA Cycle

In fact, I am going to cheat a little. And in two different ways.

First, I am going to defer to Deming and replace C for Check with S for Study. Like him, I think this gives us a better framework.

And second, I shall add in an O for Observe at the start. This is often found in Lean Production methodologies and is, I think, a useful addition (and one that takes us closer to the OODA Loop).

PDCA Cycle: Plan-Do-Check-Act \ aka Deming or Shewhart Cycle


Before we do anything, it is as well to carefully observe the current state, and characterise the issues to resolve.


Design some form of intervention or test that you hope will create the improvement or result you need.


Execute your plan and carry out the change or the test you designed. The iterative nature of the PDCA or PDSA Cycle means that small, incremental steps are usually best.


When you check the results of your test or the outcomes of your changes, what do you observe… and what do you learn from them?


Make a choice: adopt the change, adapt it further, or abandon it. Some people like A for Adjust.


The iterative nature of the cycle is fundamental. In this sense, we can view it as a precursor to Takeuchi and Nonaka’s Scrum methodology for product development. This has morphed into a widely-used project management methodology within the Agile Project Management paradigm.

What is Your experience of the PDCA Cycle?

We’d love to hear your experiences, ideas, and questions. Please leave them in the comments below.

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