A History of PDCA

But first, what is it? 

Plan-Do-Check-Act is an iterative cycle for improving processes and quality control. Popularized by W. Edward Deming, but credited to mathematician Walter Shewhart (pronounced shoe-heart), PDCA is a set of distinct steps aimed at getting a system closer to perfection through continuous improvement. Let’s look at where it came from. 

Inspired by the scientific method (hypothesize, experiment, evaluate), Walter Shewhart wrote, in 1939, a cycle of steps to ensure quality in a manufacturing process. The required iteration of steps are; specification, production, and inspection. Image 1 is a visualization of the cycle. Upon inspection, it was implied that operators must take action to improve their process based on what they learned in the inspection stage. 

Image 1: the Shewhart cycle of specification, production, and inspection.

Deming had a hand in editing Shewhart’s work. In a series of lectures in 1950 at the Japanese Union of Scientists and Engineers, he modified the Shewhart cycle into what became known as the Deming Wheel.1 Visualized in image 2, the Deming wheel adds a bit more prescription to the Shewhart Cycle. The distinct steps are; 

  1. Design a product
  2. Build the product
  3. Put it on the market
  4. Test it / find out what users think
  5. Redesign the product based on customer feedback (rinse and repeat) 
Image 2: The Deming Wheel, where (1) is designing a product, (2) build the product, (3) put it on the market, (4) find out what users think, and (5) re-design the product based on what the users said. 

At the end of the seminar, the Japanese students simplified the Deming wheel even further to the PDCA framework.2 By simplifying, the cyclical method for improving a product becomes useful across more domains, e.g. the service sector. Image 3 below visualizes the simplified version. 

Image 3: The simplified version of the Deming Wheel.

Because any system of continuous improvement would not be complete without its own set of iterations, Deming revised the PDCA framework again in 1993.3 The new iteration replaced the check step with study. Deming believed that studying was a more clear representation of what should actually happen in that stage. Checking on what happened implies a brief overview, whereas studying implies a deep dive into what changed. The deep dive is a better approach for learning than a simple check. 

In the most modern iteration, the PDCA cycle has become a full framework with the addition of three questions, authored by Gerald Langley, Thomas Nolan and Kevin Nolan.4 Those are; 

  1. What are we trying to accomplish? 
  2. How will we know that a change is an improvement? 
  3. What changes can we make that will result in an improvement?  

All included, image 4 below is their framework. 

Image 4: the Model for improvement 

My personal take is that the best methodology is actually observe-plan-do-learn-adjust. Visualized in image 5 below, my take is that a careful observation of a system or process is necessary before any improvement can take place. The plan step is for defining the problem, defining the metrics that will be measured, and developing concrete steps to make the desired improvement. Once the steps have been laid out, it’s time to assign people a set of particular responsibilities and have them execute on them. Once the work has been done, studying it to learn what really worked or did not work is necessary. Finally, if the results were not what was intended, make adjustments as needed. That likely means revisiting the observation stage, and beginning the process again. 

Image 5: my personal take on the PDCA cycle. 

Regardless of the methodology you chose to make continuous improvements in your own business or life, the act of having a simple system that you can stick to will make all the difference. Don’t take someone else’s word for it- try it yourself. Find a framework that makes sense to you, and stick with until you create a better one.


  1.  Deming, W.E. 1950. Elementary Principles of the Statistical Control of Quality, JUSE
  2.  Imai, M. 1886. Kaizen: The Key to Japan’s Competitive Success. New York: Random House, page 60
  3.  Deming, W.E. 1993.The New Economics. MIT Press. Cambridge, MA. page 135
  4.  Langley, G., Nolan, K, and Nolan, T. 1994. The Foundation of Improvement, Quality Progress, June 1994
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