The PDCA (plan, do, check and act) cycle is a method used for the continuous improvement of processes and products. It is an iterative method that represents the scientific approach to problem solving. It has universal validity, as it can be used to face any improvement activity in a rigorous and systematic way. The method is also known as the “Deming cycle”, named after W. Edwards Deming.

The PDCA cycle has four strengths that determine its reliability and effectiveness.

The first is its solid foundations. As described, the PDCA cycle is based on a scientific approach, and is a universally-recognised problem-solving method.

The cycle can also be used as guide for correct implementation of improvements, as it defines a clear, unambiguous process for problem solving. 

A further strength point is that it is not limited to definition and application of a solution, but rather it also includes a step to verify (check) and consolidate the results (act), in order to make sure the problem has been solved and to prevent it from recurring. 

Finally, it has a vast broad scope of application. The PDCA cycle can be applied to all company areas and functions, both production and management processes.

The cycle is named after its four stages or steps.

• Plan: this is the most delicate and important stage of the cycle, which determines whether or not the problem is solved and therefore the process is successful. In this step, the problem is described in detail, analysed and measured using data, and its root cause is determined. Tools used include the Ishikawa diagram, Pareto analysis, and the 5 whys technique. Once the causes of the problem have been understood, an action plan is drafted, and this will guide the next step in the cycle - do.
• The plan stage only identifies the problem, but also the objective, i.e. why the problem needs to be solved, as well as the evaluation criteria to validate the results of the improvement cycle.
• Do: in this step, the action plan defined in the plan stage is implemented. To do this, one good practice is to test hypothesised solutions, whose outcome is not yet known, in pilot areas.
• Check: in this stage, the initial situation and the situation following implementation of the actions and objectives defined in the plan stage are compared. The outcome of the comparison determines whether or not you to move on to the next stage in the cycle - act. If the objective has not been achieved, a new PDCA cycle will be applied to the same problem, carefully analysing the causes that led to the failure.
• Act: having now reached the final stage of the cycle, with the solution to the problem having been verified, this needs to be consolidated it by applying a standard, to prevent the problem from recurring. The standard becomes effective when it is shared throughout the organisation.

Following the steps in the PDCA cycle helps avoid three scenarios that normally occur when facing a problem using an unstructured approach that fails to solve it.

The first is when the plan and do phases have been completed, but then the cycle is broken. The problem is analysed and defined, and actions are identified, but the results of these are not verified, taking for granted that they will be effective.

The second possible case occurs when moving directly to action, without executing the plan. This leads to an iteration of the do stage, making a series of attempts that may not be conclusive.

The third and final scenario is when the cycle has a long analysis stage that never gives rise to actions that can be verified.

The PDCA cycle is effective when every stage is concluded. However, this is not the only factor that affects the effectiveness of the cycle. 

It may happen that the steps in the cycle are carried out by different teams or people, in which case the cycle may become less effective due to a lack of overall vision and accountability, which come from managing the PDCA cycle in its entirety. Overall vision and accountability are therefore key factors in achieving a positive outcome to the cycle.

In conclusion, it can be said that the PDCA cycle is a very powerful tool, however to make the most of it, the method needs to be applied in its entirety, having the same team manage and supervise the complete cycle.