Where PDCA comes from
PDCA is often called the Deming cycle or Shewhart cycle, after the quality pioneers who popularised it. W. Edwards Deming later preferred PDSA (Plan-Do-Study-Act) to emphasise learning over inspection. Toyota built PDCA into everyday management, and it sits underneath A3 problem solving, kaizen and standard work.
The four steps
- Plan. Define the problem or opportunity, understand the current state, find the cause and form a hypothesis: "If we change X, we expect Y." Decide how you will measure the result.
- Do. Run the change on a small scale, such as one line, one shift or one product, so risk is low and learning is fast.
- Check. Compare actual results with the prediction. Did the change work? Why or why not? What surprised you?
- Act. If it worked, standardise it and spread it. If not, adjust the hypothesis and start another cycle.
PDCA at different levels
PDCA is not only for projects. The same loop runs at every level of a well-run operation:
- Daily: a tier 1 meeting reviews yesterday's results (check) and agrees actions for today (act and plan).
- Weekly or monthly: leaders review trends and improvement work.
- Annually: strategy deployment plans, executes and reviews breakthrough objectives.
Common mistakes
- Spending most of the effort on Do and skipping Check, so nobody knows if the change worked.
- Planning without a clear, measurable prediction, which makes Check impossible.
- Running the change everywhere at once instead of testing small.
- Forgetting Act, so successful changes are never written into standard work and quietly drift back.
Example
A maintenance team believes a new lubrication interval will cut bearing failures on a conveyor. They plan the change for one conveyor, predicting fewer unplanned stops over two months. They run it, check the stop data against the other conveyors, and find a clear improvement. They act by updating the lubrication standard for all similar conveyors and scheduling a review.