The PDCA method or Deming wheel for your improvement

by iwolm
1 comment

What is and haw can be used the PDCA method?
A simple and concise explanation of how to implement and apply the PDCA to solve problems and activate the continuous improvement.

The PDCA is a tool to solve problems and is the scientific approach to problem solving.

It is a method of universal validity because it allows us to deal with any activity in rigorous and systematic way.

The PDCA term comes from the initials of the four phases in which it is possible to divide the process of problem solving, which have the following meaning:

P = PLAN = plan before you start => SAY WHAT YOU DO
D = DO = do what they set out => DO WHAT YOU SAID
C = CHECK = measure results => RECORD WHAT HAVE YOU DONE
A = ACT = standardize and create the procedure or repeat a new cycle => CONTINUOUS IMPROVEMENT

From the graphic point of view, P.D.C.A. is represented by a moving circle called the Deming wheel.

The movement stands for dynamism and continuity of the application process.



  • Identify the problem (PLAN)
    1. Identify and describe the problem by analyzing the main aspects.
      Motivate the choice that is why we face it.
      To well describe the problem it is necessary to collect data through observation and analysis.
      We only must use data and facts, not opinions, that should be checked for validity and reliability.
      Since performing a collection of all the elements that identify a phenomenon can be too expensive and last long, it is necessary to collect data only on specific samples which has to be representative and meaningful anyway.
      Significance: All data have to be numerical consistent and can be layered in various ways to make them meaningful.
      Representativeness: The data must ensure the representation of phenomenon. Among the right tools are:
    2. Define the rough objective in a clear, quantitative and comprehensive way, quantifying the benefits of ensuring its achievement, as the economic effects, both tangible and intangible.
      Times, indicators and monitoring tools must also be defined
    3. Analyze the problem that is analyze data that describe it and identify the negative effects or to the one to study, defining their importance and priorities for action. Each share of improvement must be based on objective considerations, that is, the result of the data processing, that represent the phenomenon under study in the most reliable way. A good tool for the analysis of data is the HISTOGRAM.
    4. Search all the possible causes, that is develop a complete picture of all the problem causes and identify the most likely causes (hypotheses), then test them with data collection, processing, testing, etc..
      It is necessary to find an agreement on the underlying causes of the problem and define the “law of priority”, iterating the process until you find the real proved cause.
      The most commonly used tools to identify the causes of a problem are the CAUSE EFFECT GRAPH, the BRAINSTORMING, the CORRELATION DIAGRAM, the PARETO CHART.
    5. Plan corrective action, starting from the research and analysis of the possible corrective actions and identify the most effective ones, then design activities to be performed, defining how and when, and then define the criteria to evaluate results.
  • Experience (DO) Prepare interventions by defining everything you need to implement them.
    Train the staff responsible for the implementation of corrective actions.
    Apply the corrective actions and implement the planned solutions.
    Verify the correct implementation of the actions.
  • Compare the results (CHECK) Verify that the corrective action has been carried out on schedule.
    Check the results of the actions taken and compare the data obtained with those of the starting position.
    Compare your results with your goals.
    If you have reached the goal, you can move on to Act, otherwise you need to repeat a new PDCA cycle on the same problem, critically analyzing the various phases of the above cycle in order to locate the failure causes.
  • Standardize the solution (ACT) Make the solution found a common practice (MAKE A PROCEDURE) so that the corrective actions can be consolidated and irreversible.

It is also necessary to make a specific and thorough training of the operators and to program checks on the validity of corrective actions, establishing from the outset how and when.

If necessary, prepare a new plan by activating a new phase of PDCA on the same subject for further improvement => activation of CONTINUOUS IMPROVEMENT.

Systematic use of PDCA.

The PDCA method can be used for continuous improvement, enabling the three cycles described below.

    This is the cycle that is positioned downstream of the phases PLAN and DO and has the aim of verifying whether what was planned and implemented still return the expected results.
    In case of positive CHECK, the ACT phase consists in maintaining the current status and continuing to monitor the compliance with requirements.
    On the other hand, if CHECK is negative, it’s necessary to reactivate the cycle of the corrective action.
    If the result of CHECK is negative, (the results are not what you want), you turn on the cycle of the corrective action to rectify the situation.
    The cycle is characterized by two components:

    • the remedy, that is the immediate action designed to correct the effects
    • prevention, that is the planned action aimed at removing the causes.

    When the CHECK is positive again, you activate the maintenance cycle again.

    This cycle requires a proper implementation of the first two ones since the improvement is more effective the more stable is the initial situation.
    The improvement cycle is activated when, despite the maintenance cycle indicates positive results, it is necessary that new ideas arise on how to do better, in a way more simple, less expensive, faster, more secure, etc..
    It is therefore necessary to start from the PLAN step because it is necessary to “design” new actions to achieve new goals.
    If, after the implementation of these actions (phase C) the CHECK is successful, you can go back to the maintenance cycle, otherwise you have to activate the corrective one.

How to create a histogram

The histogram is a bar graph that shows the variability of a phenomenon making it easier to interpret the data.
If the factors that affect the processes (man, machine, material, method, etc.) were perfectly constant, the data generated by the processes would all have the same value.
Actually this never happens, so it is inevitable to have some variability in the values.
The use of the histogram is aimed at the study of such variability, through the analysis of the shape of their distribution, the mean value and the dispersion.
It also allows to evaluate the significance of any differences between the expected result (specification) and what was actually achieved, providing guidance on the possible causes of such deviations.
The histogram is also an important tool in monitoring processes.

The construction of the histogram takes place according to the following steps:

  1. Collection of N data on the phenomenon
    Xi = output characteristic of a process
  2. Calculation of the variation range
    R = X max – X min (maximum value – minimum value) / li>
  3. Determination of the number of classes
    K = N ½
  4. Calculation of the class amplitude
    h = R / K
  5. Calculation of class limits
    Class 1: (X min) / (min X + h)
  6. Construction of the frequency table
  7. Definition of the Cartesian axes
    X = characteristic
    Y = frequency
  8. Representation with data bars showing data in the frequency table.

How to create a cause and effect diagram

The CAUSE – EFFECT diagram is a form of structured and logical representation of the connection between an effect and its related causes.
With the term effect is meant any problem you want to analyze. It can be a type of defect, a quality feature, a parameter of productivity etc..
The purpose of this diagram is the search for the causes of a problem, that is a prerequisite for its solution.
Only by identifying the real causes it is possible to determine the appropriate improvement actions aimed at their elimination.
The perspective is that of preventing problems through actions that act on the causes rather than the correction of the same with remedies in order to maximize the effects.

The application of the diagram provides three distinct phases:

  1. Construction of the diagram
    Referring to a specific effect to be analyzed (clearly defined), you can identify all the possible causes.
    These cases can be structured in large families, such as:

    • Method
    • Machines
    • Labor
    • Materials

    or for stages of the process

  2. Selection of cases
    Of all the possible causes you select those considered the most influential. This assessment is based on historical data or data collected ad hoc and on the people experience.
  3. Check the causes
    through data collection and appropriate testing, you verify real influence of the selected causes to identify those priority.

How to create a Pareto chart

It is very useful to use the Pareto chart as it allows an immediate and effective graphical representation of the priority aspects of a problem.
In this way it is possible to concentrate the available resources on them, increasing both the probability of success and the entity itself of obtainable improvements.
The use of Pareto diagram is possible in any field, and offers a valuable support in the planning step because you can determine which areas has to engaged in relation to the objectives.

The application of the diagram includes:

  1. Construction of the frequency table
    Based on the collected data, you build a table in which the various items of classification (CLASS), the corresponding frequencies of occurrence (absolute and cumulative) and incidence rates (absolute and cumulative) are listed in descending order.
    The non relevant elements are instead grouped in the class “Others” in order to make more evident the identification of priority.
  2. Construction of the diagram
    You can trace the horizontal axis, on which are shown different classification items, and the vertical axes, concerning the frequencies of occurrence and the percentages.
    Based on the data in the table, for each item of classification, you can built bars of length and height corresponding to absolute values and percentages.
    You can also trace the so-called cumulative curve, which represents the progressive sum of occurrence frequencies and relative percentages.

Considering the identification of priorities for action, you may want to also build the diagram for costs.
Often, in fact, to problems of modest numerical relevance may correspond high costs.

Summary of the method PDCA


  • Identify the problem
  • collect data
  • define the objectives
  • analyze the causes
  • define and suggest solutions


  • apply the corrective actions
  • monitor the implementation


  • verify the results of the actions taken
  • compare with objectives


  • make the solution found a common practice
  • prepare a new phase of plan.


You may also like

1 comment

edgar August 12, 2014 - 4:19 pm

Interesting, thank you for sharing.


Leave a Comment