The Deming Cycle (also called the Deming Wheel or Shewhart Cycle) is a four-step, iterative approach to solving problems and improving processes, most commonly known by the acronym PDCA (Plan-Do-Check-Act). Its roots trace to physicist Walter Shewhart, who described a three-step linear process (specification, production, inspection) at Bell Labs in the 1920s and 1930s. W. Edwards Deming, Shewhart’s colleague, expanded it into a four-step iterative cycle and popularized it in Japan starting in 1950.
Here’s the detail most sources skip entirely: Deming himself rejected the name “PDCA.” In a personal letter, he called it “the corruption” of his cycle and insisted on PDSA (Plan-Do-Study-Act) instead, because he believed the word “Check” wrongly suggested passive inspection rather than genuine learning.
Quick Reference Table
| Term | What It Means | Origin |
| Shewhart Cycle | The original three-step process: specification, production, inspection | Walter Shewhart, 1920s–1939 |
| Deming Wheel / Deming Cycle | Deming’s four-step expansion, first presented in Japan | W. Edwards Deming, 1950 |
| PDCA | Plan-Do-Check-Act; the name Japanese engineers gave Deming’s cycle | Popularized in Japan post-1950; formalized by Mizuno, 1959 |
| PDSA | Plan-Do-Study-Act; Deming’s own preferred, corrected version | Deming, publicly restated in 1986 and 1993 |
Key Takeaways
- The cycle didn’t start as four steps, or with Deming. Walter Shewhart described a three-step linear process, specification, production, inspection, at Bell Labs, which Deming later expanded and made iterative.
- Deming presented his four-step cycle in Japan in 1950, initially calling the fourth step something closer to “redesign through marketing research,” not yet the “Act” most people know today.
- Japanese engineers, not Deming, coined “PDCA.” The Plan-Do-Check-Act label was a later interpretation and simplification of Deming’s original teaching, with Shigeru Mizuno often credited with formalizing it around 1959.
- Deming explicitly rejected “PDCA” later in his life. In a 1990 letter to Ronald Moen, he called it “the corruption,” and by 1993 he was publicly insisting on PDSA, referring to it as “the Shewhart Cycle for Learning and Improvement.”
- The disagreement was about more than wording. Deming felt “Check” carried a connotation of “hold back” or pass/fail inspection, while “Study” implied genuinely analyzing what was learned, whether the result matched the prediction or not.
- Despite Deming’s objection, “PDCA” remains the more common term in practice today, including at Toyota, where it’s the officially recognized framework rather than PDSA.
- The “Do” step is about testing a plan on a small scale, not analyzing data. A common point of confusion is blending Plan-phase problem analysis into the Do step; Do is specifically where the plan gets carried out, ideally as a small, low-risk pilot.
Public, Onsite, Virtual, and Online Six Sigma Certification Training!
- We are accredited by the IASSC.
- Live Public Training at 52 Sites.
- Live Virtual Training.
- Onsite Training (at your organization).
- Interactive Online (self-paced) training,
What Is the Deming Cycle?
The Deming Cycle, also known as the Deming Wheel or the Shewhart Cycle, is a four-step, iterative method for improving a process or solving a problem: Plan, do the work, check or study the results, and act on what was learned, then repeat. Its defining feature is that it’s a cycle, not a one-time linear project; each pass through the loop is meant to feed directly into the next one, building knowledge incrementally over repeated iterations.
Where the Deming Cycle Actually Came From?
The cycle’s origin predates Deming himself. Walter A. Shewhart, a physicist and statistician at Bell Labs, described a three-step scientific process in his 1939 work Statistical Method from the Viewpoint of Quality Control: specification, production, and inspection. This was originally a linear process, not yet the repeating loop most people associate with the concept today.
W. Edwards Deming, who had known and worked alongside Shewhart since the late 1920s, took this linear three-step process and reshaped it into an iterative, four-step cycle. In 1950, Deming presented this expanded version to the Japanese Union of Scientists and Engineers (JUSE).
Japanese engineers who learned the concept from Deming’s teaching, credited in various accounts to Kaoru Ishikawa and formalized by Shigeru Mizuno around 1959, condensed it into the label most people know today: Plan-Do-Check-Act, or PDCA.
Also Read: What is the PDSA Cycle and Why It Matters?
The Four Steps, Correctly Explained
A common source of confusion, including on earlier versions of Six Sigma glossary content, is blending the boundaries between these four steps. Here’s each one defined clearly:
- Plan: Investigate the current situation, understand the actual problem, and develop a specific plan with a clear, testable prediction of the expected outcome.
- Do: Carry out the plan, ideally as a small-scale pilot rather than a full rollout, specifically to limit risk if the plan doesn’t work as expected.
- Check (or Study): Examine what actually happened during the Do step, and compare it honestly against what the Plan step predicted would happen.
- Act: Based on that comparison, either adopt the change as standard practice, adjust and run the cycle again, or abandon the approach and start over with what was learned.
A specific correction worth making directly: analyzing data to identify the real underlying problem belongs in the Plan step, not the Do step. The Do step’s job is narrowly to execute the plan, preferably at a small, controlled scale, not to perform the analysis itself.
Why Deming Rejected “PDCA” and Insisted on “PDSA”
This is the single most important, and most frequently omitted, part of this topic, and it’s worth stating plainly because it’s genuinely surprising to many practitioners: the man the cycle is named after didn’t like the name most people use for it.
By the 1980s, Deming was actively and publicly correcting people who called it PDCA. In a personal letter to Ronald Moen in 1990, Deming wrote to “be sure to call it PDSA, not the corruption PDCA.” In his 1993 book The New Economics, he stated directly that PDCA was the wrong terminology and that the correct version was PDSA: Plan-Do-Study-Act.
Why did the specific word matter so much to him?
Deming felt that “Check,” in English, carries a connotation tied to inspection, auditing, and pass/fail verification, activities that happen after an outcome and focus on judging it. He believed genuine improvement requires learning, not judging. “Study” was his replacement precisely because it implies deeper analysis: not just “did it work, yes or no,” but “what did we actually learn, including from anything unexpected.”
According to the Deming Institute’s own account, Deming’s focus in this step was on comparing real, observed results against a prediction made during Planning, and using any gap between the two to refine the underlying theory, not simply to grade the outcome pass or fail.
Does It Actually Matter Today: PDCA or PDSA?
In practical terms, both names describe essentially the same underlying cycle, and the debate is more historical and philosophical than operational.
PDCA remains the far more common term in actual use today, including as the officially recognized framework at Toyota, one of the organizations most closely associated with disciplined continuous improvement. PDSA is used more by those following Deming’s own writing and the Deming Institute directly, particularly in healthcare quality improvement circles, which have historically leaned toward Deming’s original terminology.
For a Six Sigma practitioner, the practical takeaway isn’t which acronym to use, most training and most workplaces will keep using “PDCA”, it’s the substance behind Deming’s objection: treat the third step as genuine analysis and learning, not a simple pass/fail check, regardless of which letter you use for it.
How Does the Deming Cycle Compare to DMAIC?
Both are iterative, structured improvement methods, but they differ in depth and origin.
SSDSI’s own DMAIC vs. PDCA comparison covers this in full detail; the short version is that DMAIC (Define, Measure, Analyze, Improve, Control), a Six Sigma-specific methodology, generally provides more structured, statistically rigorous phases suited to complex problems, while the Deming Cycle’s four broader steps are lighter-weight and more universally applicable across almost any kind of process or improvement effort, technical or otherwise.
Real-World Example (Hypothetical)
Problem: A customer support team wants to reduce how often a specific type of ticket gets escalated unnecessarily, but has no clear theory yet about why it’s happening.
Analysis: The team applies the cycle correctly, following Deming’s own emphasis on prediction and learning rather than simple pass/fail checking.
Six Sigma approach: Plan — the team forms a specific, testable prediction: adding one additional clarifying question to the initial ticket form will reduce unnecessary escalations by identifying the real issue earlier. Do — the new question is piloted on a single support queue for two weeks, not rolled out company-wide immediately. Study — the team compares actual escalation rates in the pilot queue against the original prediction, and specifically examines a handful of tickets where the new question didn’t help, not just the overall pass/fail number.
Action: The Study step reveals the new question helps for one ticket category but not another, refining the team’s original theory rather than simply confirming or rejecting it outright.
Result (hypothetical): Acting on that refined understanding, the team rolls out the question specifically for the ticket categories where it demonstrably helped, rather than either abandoning the whole idea or blindly deploying it everywhere. This is a hypothetical illustration of the cycle applied with a Study, not just Check, mindset, not a documented case study.
Also Read: Cycle Time Reduction: Strategies to Boost Efficiency
Common Mistakes When Applying the Deming Cycle
- Treating the third step as a simple pass/fail check. This is precisely the shallow interpretation Deming spent years pushing back against; the real value comes from studying why a result did or didn’t match the prediction.
- Skipping the small-scale pilot in the Do step. Rolling out a full, untested change directly increases risk if the underlying theory turns out to be wrong.
- Blending data analysis into the Do step. Understanding the real problem is Plan-step work; Do is specifically for executing the plan.
- Treating one pass through the cycle as the finish line. The cycle is meant to repeat, refining the underlying theory with each iteration, not conclude after a single loop.
- Assuming “PDCA” and “PDSA” describe fundamentally different methods. They describe the same underlying cycle with a genuine, but philosophical, difference in emphasis on the third step, not two competing frameworks.
Frequently Asked Questions on Deming Cycle
Q: What is the Deming Cycle?
A: The Deming Cycle is a four-step, iterative method for improving a process, commonly known as PDCA (Plan-Do-Check-Act) or, in Deming’s own preferred terminology, PDSA (Plan-Do-Study-Act). It builds on Walter Shewhart’s earlier three-step linear process.
Q: Who invented the Deming Cycle?
A: Walter Shewhart described the original three-step linear version (specification, production, inspection) in 1939. W. Edwards Deming expanded it into the iterative four-step cycle and presented it to Japanese engineers in 1950.
Q: What is the difference between PDCA and PDSA?
A: They describe the same underlying cycle. PDCA uses “Check” for the third step, implying inspection or a pass/fail judgment. PDSA uses “Study,” Deming’s own preferred term, implying deeper analysis and learning from both expected and unexpected results.
Q: Did Deming really reject PDCA?
A: Yes. In a 1990 letter to Ronald Moen, Deming called PDCA “the corruption” of his cycle, and in his 1993 book “The New Economics,” he stated directly that PDSA was the correct terminology.
Q: What is the Shewhart Cycle?
A: The Shewhart Cycle refers to Walter Shewhart’s original three-step process, specification, production, and inspection, described in 1939, which Deming later expanded into the four-step iterative cycle that bears his name.
Q: How is the Deming Cycle different from DMAIC?
A: DMAIC (Define, Measure, Analyze, Improve, Control) is a more structured, statistically rigorous Six Sigma methodology built for complex problems. The Deming Cycle’s four broader steps are lighter-weight and more universally applicable across nearly any process improvement effort.
Final Words
The Deming Cycle’s real story is more interesting than the simple four-letter acronym most people learn: it began as Shewhart’s linear three-step process, became Deming’s iterative four-step cycle, and then, in a detail most sources skip entirely, Deming spent years publicly rejecting the very name most people now use for it. Whether an organization calls it PDCA or PDSA matters far less than whether it actually follows Deming’s original intent for the third step: studying and learning from a result, not just checking whether it passed or failed.
Understanding the real history and intent behind the Deming Cycle, especially Deming’s own insistence on genuine study over simple pass/fail checking, deepens how a practitioner actually applies continuous improvement day to day.
Six Sigma Development Solutions, Inc. (SSDSI) is IASSC-accredited and 5-star rated on Google Reviews, having certified 5,322+ professionals across 600+ organizations in 52 cities. Our onsite, live virtual, public, and online training covers PDCA, DMAIC, and the full history and application of continuous improvement methodology. Explore SSDSI’s Green Belt certification to build that foundation.
About Six Sigma Development Solutions, Inc.
Six Sigma Development Solutions, Inc. offers onsite, public, and virtual Lean Six Sigma certification training. We are an Accredited Training Organization by the IASSC (International Association of Six Sigma Certification). We offer Lean Six Sigma Green Belt, Black Belt, and Yellow Belt, as well as LEAN certifications.
Book a Call and Let us know how we can help meet your training needs.
