PDCA / PDSA Cycle or Deming Cycle

- techniques and best practice to obtain the best results from brainstorming when used as a quality tool for problem solving.

The Deming cycle or Shewart wheel is also called the PDCA cycle - Plan-Do-Check-Act or PDSA cycle - Plan-Do-Study-Act.

Whatever the name, the PDSA cycle is a key element within process improvement.

It forms one of the key processes within any process improvement strategy. The cycle has been in use for many years.


PDCA, Shewart, Deming cycle background

PDCA was popularised by Dr Deming, a mathematician and statistician who became very involved in quality control methodology.

He took the basic concept of the Plan-Do-Check-Act, or PDCA cycle and used it to help improve quality of manufacturing processes.

Later Deming modified the name to PDSA, as he felt that the word check emphasised aspects of inspection rather than a more in-depth analysis. Accordingly he changed the process name to Plan-Do-Study-Act, PDSA.

Deming, when referring to the cycle with a name always referred to it as the Shewart cycle after another American statistician who had an involvement in quality control.

The work by Deming and Shewart and Deming can be traced back to early scientific method developed by Francis Bacon - Novum Organum, published in 1620. In this work he described the method of working as hypothesis-experiment-evaluate or plan, do and study.


PDCA, PDSA cycle basics

As the name indicates the PDCA cycle, Plan-Do-Check-Act, or Plan-Do-Study-Act, PDSA cycle consists of four main stages.

The concept behind the cycle is that it is an on-going process, and it undertaken repeatedly to ensure the optimum performance improvements. Also it may be undertaken to check that processes are still operating within their required tolerances and not slipping out due to external factors.

Continuous process improvement methodology

As the name of the cycle implies, there are four main stages in the PDSA, PDCA cycle.

  • Plan:   The Plan stage of the PDSA or PDCA cycle is particularly important. It sets out the parameters for the whole process - this will include the output expectations including the objectives and goals.
  • Do:   This stage of the cycle involves the actual implementation of the plan including the collection of data. Not only does it include the implementation or doing of the plan, but it also includes collecting the relevant measurement data or metrics.
  • Check / Study:   The stage of the cycle involves studying the results obtained in the previous stage, looking for deviations from expected results, etc.. Note that it can often be beneficial to present data in charts and graphs to make trends more visible.
  • Act:   In this part of the PDSA cycle, it is necessary to define and implement corrective actions on areas where there are significant differences between actual and planned results. It is important to analyse the results to determine the root causes wherever possible. Once this has been achieved, it is possible to implement the process improvement changes.

The PDSA / PDCA cycle is iterative. So, once it has competed, it is necessary to return to the beginning and see what further improvements can be made.

By Ian Poole


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