Plan-Do-Study-Act Cycle

The plan-do-study-act (PDSA) cycle consists of a circle or a wheel as depicted in Figure 1. The wheel is divided into four quadrants, each representing a significant step in the quality improvement process. The continuous, circular motion of the PDSA cycle symbolizes the central component of the quality improvement philosophy—that improvement is a never-ending cycle, a continuous movement, as opposed to a linear project with a discrete beginning and ending. The PDSA cycle is often referred to as “the Shewhart cycle” or “the Deming cycle” after the two men who were instrumental in its conception and dissemination.

Statistician Walter Shewhart (1891–1967), employed by Bell Laboratories in the 1920s and 1930s, pioneered the use of new statistical methods to improve the quality of manufactured goods. At the time, quality inspection in the manufacturing industry consisted of using classical statistical techniques to detect products that were outside of the specification limits. Shewhart introduced the use of statistical process control tools that could be used to forecast or predict. This contradicted the linear manufacturing model, which was to specify, produce, and inspect. In proposing a circular, closed-loop model, Shewhart emphasized that each area of production requires statistical knowledge from each of the other areas. Shewhart's work promoted a fundamental change of focus from detection to prevention. Integral to this change was his emphasis on work processes rather than the manufactured goods themselves. Shewhart asserted that proper control of the processes of production was far more efficient than end point inspection of the product.

Figure 1 The Plan-Do-Study-Act (PDSA) Cycle

Quality expert W. Edwards Deming (1900–1993) studied Shewhart's work, expanded upon it, and is credited with disseminating it throughout the world. In 1950, Deming presented an influential series of lectures to Japanese engineers and top executives. In the lectures he explained the meaning and use of the PDSA cycle. The four stages of the PDSA cycle are as follows:

• Plan: The quality team plans a change or tests a pilot program by first observing and analyzing the current process. This establishes a baseline from which to later evaluate the effectiveness of the team's actions. Throughout this step, team members ask, “What is the purpose of this change or test?”
• Do: Next, the plan is implemented, preferably on a small scale. All relevant changes that occur during the implementation are documented, and all data are collected systematically for later evaluation.
• Study or Check: The effects of the change or test are then measured and evaluated. The team asks itself, “Has the purpose been achieved?”
• Act: Depending on the outcome of the evaluation, the change is acted on or tested. If the test result is positive, the change is standardized to remove variation in the process, and the cycle begins again.

[Page 436]In teaching the PDSA cycle, Deming emphasized the central role of the customer in the learning cycle. He asserted that there are many stages of work and these stages all form a process. If you look at a single process, every stage of that process has a customer—the next stage. In the final stage, there is an ultimate customer, the one who buys the product or the services. Thus the customer plays a significant role in planning for the future by helping clarify what needs to be done for improvement. Thus the PDSA cycle represents a never-ending cycle of learning in which the results of a change must be studied, analyzed, and acted on in a scientific manner.

...