PDSA / Plan-Do-Study-Act (or Adjust)

PDSA stands for Plan-Do-Study-Act, or less commonly, Plan-Do-Study-Adjust.

It is a structured, iterative problem-solving approach popularized by W. Edwards Deming, who originally was mentored on the process by Walter Shewhart. With that origin in mind, it should come as no surprise that this method is also known as the Deming cycle.

PDSA Background

Most of the continuous improvement world considers the Deming cycle to be PDCA, or Plan-Do-Check-Act. In the later years of Deming’s career, he used PDSA instead of PDCA. The story goes that Deming claimed that he intended it to be PDSA all along, but he was mis-translated when he first taught this method in post-World War II Japan.

Study vs. Check

Those who understand the Deming cycle know that the third step is intended to uncover a deep understanding of the new process with the changes that you have made in place. That more closely aligns with “study” than with “check”.

The problem is that those who are not well versed hear “check” and think of it as a much more cursory confirmation that the changes were effective. In some cases, a quick look will get you the right answer. But sometimes, even though the results look positive, they were not exactly as expected. The Deming cycle requires a great deal of prediction. It’s not enough to get the right result. You have to get the right result in the way that you thought it was going to happen. Otherwise, it was just luck. The problem you thought you solved is likely to recur.

The reality though is that PDCA is far too embedded in the Lean community to have much of a chance of being replaced. That’s not to say that it is better than PDSA. Despite this entrenched terminology, I encourage you to use and more importantly teach PDCA as if it actually were Plan-Do-Study-Act.

Act vs. Adjust

In addition to the third letter, there is also apush, albeit a lesser one, to use “adjust” as the final letter. The premise here is that you will seldom get things completely right. Even in the best of cases, you have to make some minor changes to the process. Most people view this as less conditional than “act”, which is often done only when the check is not up to par.