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The plan-do-check-act (PDCA) cycle has been an integral part of quality management for several decades. Today, the ISO 9001 quality management standard specifies use of the PDCA model for managing processes and creating process oriented thinking.
As I reflect on what I perceive to be the limited success of ISO 9000 standards to date and review the emphasis on inspection and testing in ISO 9001, I have some questions.
For example, why is check included in the cycle when the goal is to reduce the need for verification activities? Several factors related to the cost of poor quality and current demands for quality in terms of Six Sigma and virtual perfection also make me question the role of PDCA.
I therefore decided to investigate its evolution and role and to propose a new process management model I call the 4P's cycle.
Evolution of PDCA
PDCA's evolution began with the dawn of the modern tools of quality in the 1920s (see sidebar "PDCA's Beginnings").
PDCA is a continuous feedback loop to identify and change process elements to reduce variation. In other words, the objective of PDCA is to plan to do something, manufacture or do it, verify or check it for meeting requirements, and correct the process to maintain the acceptable output performance.
However, literature shows W. Edwards Deming must have realized maintaining or controlling a process was not good enough. He relabeled the feedback cycle of gaining knowledge as the PDSA (plan-do-study-act) cycle for continuous improvement, as shown in Figure 1.1
Accordingly, the study of variation in process output is important to continually improving the process. PDCA can be used to identify the need for an improvement, and PDSA can be used to sustain improvement.
PDSA emphasizes study of excessive variation with respect to the acceptable limits and identification of causes of excessive variation for necessary adjustment rather than identifying the root causes of the problem.
It is apparent the PDSA cycle was intended to go beyond Shewhart's out of control action plan. Deming must have recognized there must be a tendency toward continuous reduction in variation to keep it within customer specified limits.
Somehow, PDSA did not get as much visibility as PDCA, which became a default method to manage a process. As a...