In one line: Plan a small change, do it, check what happened against what you expected, and act on what you learned, then repeat. It is the universal loop of continuous improvement.
Core idea
The Plan–Do–Check–Act cycle is the engine of continuous improvement. It is associated with W. Edwards Deming, who popularized it (he preferred Plan–Do–Study–Act, emphasizing learning over inspection), building on Walter Shewhart’s earlier work on statistical control [1]. Its power is in the loop: every improvement becomes the new baseline for the next one, and every failed experiment is still a lesson.
flowchart LR P["Plan<br/>define the problem,<br/>predict the result"] --> D["Do<br/>try it on a small scale"] D --> C["Check<br/>compare results<br/>with the prediction"] C --> A["Act<br/>adopt, adapt,<br/>or abandon"] A --> P
How it works
- Plan: state the problem and the goal, find the likely causes, and decide on a change, including a prediction of what it will do.
- Do: carry out the change, preferably as a small, low-risk trial, and collect data.
- Check (study): compare the results with the prediction. What happened, and why did it differ?
- Act (adjust): standardize the change if it worked, modify it if it partly worked, or drop it and try another idea. Then start the next cycle.
The course version reads the last step as Adjust, which is a reminder that the point of the loop is to change course based on evidence.
In practice
PDCA scales from a single engineer’s workflow to a whole program. It applies to:
- a test procedure improved cycle by cycle;
- a team’s sprint retrospective (see Scrum);
- a company-wide quality campaign;
- personal habits, such as forecasting your weekly hours, comparing actuals, and adjusting next week’s plan.
The most common failure is skipping Check: making changes and moving on without comparing results against the prediction, so nothing is learned.
Questions to ask yourself
- What did I predict would happen the last time I changed a process, and did I check?
- Which recurring problem on my team would benefit from one small, measured experiment?
- Do we standardize what works, or rely on heroes to remember it?
Connections
- The philosophy behind it: Deming’s Quality Philosophy, Total Quality Management.
- Structured versions: Six Sigma (DMAIC), Scrum (sprints).
- Organizational use: Adaptive and Transformational Change.
- Capabilities exercised: Realizing the Vision, Decision Making, Inquiry.
Sources
- ASQ - PDCA Cycle and Deming’s 14 Points [1]
- Deming’s account of the management system behind the cycle [2]