An In-Depth History of the Kaizen PDCA Cycle

An In-Depth History of the Kaizen PDCA Cycle

Kaizen works to improve two things: Processes and End results (i.e. products, services, etc.).

Lean organizations focus on improving all parts of a process from start to finish in order to increase the quality of the results. Through the use of specific cycles (like PDCA), organizations can improve the processes and end products.

Shewhart's Straight-Line Process

In 1939, in Shewhart's published book, Statistical Method From the Viewpoint of Quality Control, Shewhart introduced a three step, straight line concept of scientific processes. In his specification, production, inspection process Shewhart applied the scientific method.

Step One > Step Two > Step Three
Specification Production Inspection

Later, Shewhart changed the steps to be a recurring, circular concept.

The Deming Wheel

Deming studied Shewhart's straight-line process and modified the concept, adding his own ideas. In 1950, Deming presented his version as what he referred to as the Deming Wheel, The Deming Cycle, and the Deming Circle.

The Deming Wheel is a 4-step, cyclical process. There should be a constant cycle through design, production, sales, and research to produce quality service and products.

Deming Wheel Cycle

  • The product should be designed (with applicable tests occurring)
  • The product should be made and tested in the lab and tested in the production line.
  • The product should be sold.
  • The product must be tested through market research and through using it. One must figure out what users think about the product and why other people have not yet purchased the product.

1951 Japanese PDCA Cycle - Plan, Do, Check, Act

In 1951, the Deming Circle was reworked by the Japanese. It was developed into the PDCA (Plan, Do, Check, Act) Cycle. Masaaki Imai wrote that the Deming Circle was developed into the PDCA cycle by Japanese executives but did not specify who.

The PDCA Cycle steps:

  • Plan: Describe an issue and postulate potential causes and resolutions
  • Do: Implement the plan.
  • Check: Analyze the results to verify whether or not the plan has had the intended effect.
  • Act: If the results of the cycle were not satisfactory go back to plan. If the results were satisfactory, standardize the solution.

1985 Japanese PDCA Cycle - Plan, Do, Check, Act

In 1985 the PDCA Cycle was revised, utilizing additions from Kaoru Ishikawa.

The Japanese PDCA cycle was changed to include other things within the Plan, Do, Check, Act steps:

  • Plan: Now divided into two steps - define goals and targets as wells as decide on ways to reach the end goal.
  • Do: Now divided into two steps - “ participate in education and training as well as implement the plan.
  • Check: Analyze the results to verify whether or not the plan has had the intended effect.
  • Act: If the results of the cycle were not satisfactory go back to plan. If the results were satisfactory, standardize the solution.

The PDCA cycle functions a bit like the scientific method with people testing out hypotheses to see what works and then developing new procedures based on outcomes.

A key thing to remember is that these cycles are ongoing. Standards are important to have, but they aren't set in stone. Workplaces are dynamic and business conditions change, so standards must change, too.

Shewhart Cycle

In 1986, Deming revealed a modified Shewhart cycle. He confirmed that it was a revised version of the original 1950s version.

The new cyclical steps were:

  • "What could be the team's most important accomplishments? What changes might be desirable? What data are available? Are new observations needed? If yes, plan a change or test. Decide how to use the observations.
  • Carry out the change or test decided upon, preferably on a small scale.
  • Observe the effects of the change or test.
  • Study the results. What did we learn? What can we predict?
  • Repeat step one, with knowledge accumulated.
  • Repeat step two, and onward.

Shewhart Cycle for Learning and Improvement - The PDSA cycle

PDSA Cycle - Plan, Do, Study, Act

In 1993, Deming changed the Shewhart's Cycle to the Shewhart Cycle for Learning and Improvement, also known as the PDSA (Plan Do Study Act) Cycle. He did this because he believed that "check" was seen to mean "hold back" to inspect instead of analyzing.

The cyclical steps of PDSA are:

  • Plan: "Plan a change or test aimed at improvement"
  • Do: "Carry out the change or test (preferably on a small scale)"
  • Study: "Examine the results. What did we learn? What went wrong?"
  • Act: "Adopt the change, abandon it or run through the cycle again."

PDSA Cycle and Model for Improvement - Plan, Do, Study, Act

Deming's PDSA cycle was added to in 1991 by men named Moen, Nolan, and Provost. To the "Plan" step of the PDSA cycle, the men added the requirement of using prediction and associated theory. They also asserted that the "Study" step of PDSA relates the witnessed data to the prediction as a foundation for learning. The men pointed out that it wasn't enough to conclude that a change brought about improvement, you will also need to be able to predict if a change will result in improvement under different future circumstances.

In 1994, Nolan, Provost, and a man named Langley added the "Model of Improvement" questions to the PDSA Cycle. It consists of these three questions:

  • "What are we trying to accomplish?" 
  • "How will we know that a change is an improvement?"
  • "What change can we make that will result in improvement?"

The Deming Circle VS. PDCA

In August of 1980, Deming was involved in a Roundtable Discussion on Product Quality--Japan vs. the United States. During the roundtable discussion, Deming said the following about his Deming Circle/PDSA and the Japanese PDCA Cycle, "They bear no relation to each other. The Deming circle is a quality control program. It is a plan for management. Four steps: Design it, make it, sell it, then test it in service. Repeat the four steps, over and over, redesign it, make it, etc. Maybe you could say that the Deming circle is for management, and the QC circle is for a group of people that work on faults encountered at the local level."

SDCA Cycle - Standardize, Do, Check, Act

The SDCA Cycle is a modified version of the PDCA (Plan, Do, Check, Act) Cycle.

To create the best products possible in the best way possible, people must follow best practices, often referred to as standard work or standardized work. The SDCA cycle maintains standards, while the PDCA cycle improves them.

To maintain standards:

  • Standardize: When a problem occurs, identify what the current standards are.
  • Do: Use current standards.
  • Check: Make sure the standards are effective.
  • Act: Continue using the standards to stabilize the process.

This process - the SDCA cycle - occurs as part of daily work to make sure that work is up to par. When people discover a problem and find that the standards themselves are part of the problem - ”the standards could be preventing a process from occurring faster, easier, safer, etc.


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