Tools used in quality management

6.3.1. The seven quality tools

From the multitude of techniques which support the problem solving process, it is the seven statistical tools, which are also referred to as QC (Quality Control) tools that have become the most firmly established. Some of the individual methods have been used for decades or have been borrowed from other disciplines. They form a methodological tool, which can be used to structure and visualize complex issues and which thus supports all phases in the problem- solving process (PDCA). They are particularly suitable when all of the data needed to solve the problem are available and particularly suitable when all of the data needed to solve the problem are available and have to be analyzed.

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Cause and effect diagram

The cause and effect diagram, also known as the Ishikawa or fishbone diagram, is a tool which can be used to analyze facts with a view to identifying the cause of a defined effect. The problem, or the effect, is entered in the head of the fish; the bones represent the main influencing variables. The individual causes are entered inside the bones. The principle influencing variables frequently correspond to the 7M checklist (Man, Machine, Material, Method, Marginal conditions, Management, and Measurement).

Histogram

Histograms help to interpret the reasons for scatter by displaying the distribution of data values. The data values are divided into classes in accordance with statistical rules. These form the abscissa of the diagram. The number of data values per class is shown on the y-axis. The average value and type of scatter are shown by the distribution curve.

Correlation diagram

Scatter or correlation diagrams describe graphically whether there is a correlation between two variables (problem and influencing variable). Plotting the factors in relation to one another in a x-y diagram yields information as to the nature of the correlation between the factors. This is achieved by plotting a sufficient number of pairs of values, formed by altering the problem variable and determining the associated influencing variable, as measured points in the diagram. The nature of the correlation (strong or weak, positive or negative) is shown by the distribution of the points. This permits conclusions to be drawn as to potential cause.

Flow chart

The term flow chart is a general term used to describe the common forms of presentation such as bar, line, pie and spider charts. Depending on the purpose of the analysis, one or other form of visualization is suitable for demonstrating correlations or flows.

Control chart

Data collection is the starting point for improvement activities. Control or SPC charts are used to take samples at regular intervals and enter the measured valued or the statistical parameters (e.g.. average value, scatter or spread) into the SPC chart. It may become necessary to intervene in the process, depending on the control limit specified and the characteristic progress of the data values.

Pareto analysis

People are frequently faced by a number of problems or causes of faults that cannot be processed simultaneously. It makes sense to deal with the greatest, most important or most – cost-intensive problem first. Pareto Analysis (also known as ABC Analysis or Lorenz Distribution) visualizes the rank order of the influencing variables of relevance to one particular issue. These are listed in order of the level of influence they exert and their numerical significance and cumulative percentage are shown accordingly. In the course of

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investigating a quality issue, it often emerges that only a few of the many causes identified are actually very important while many of the remainder are very insignificant.

Frequency distribution

The frequency of the occurrence of individual types of faults and the frequency with which data values occur at certain intervals in the range can be presented in the form of frequency distributions. Fault clusters at individual points can thus be recognized and the causes investigated.

6.3.2. The seven management tools

Where complex problems and incomplete data collections are involved, the analysis and solution identification tools described above are insufficiently effective. In reality, many facts are described only by fuzzy data and information which has been passed on on only verbally. This verbal information must be put into a form conductive to decision-making, by means of new, suitable tools. The seven new management tools have been defined in order to supplement the tools previously described.

Each of these seven new management tools is very effective in itself. However, there is additional benefit to be gained from combining them. The combined effect of the seven new management tools is described in the following.

Affinity diagram

Affinity diagram are used to collect and classify ideas. In a brainstorming session, the individual ideas are noted on cards and then classified according to the subject to which they relate. This focuses attention and concentration on individual aspects within the problem solving process. Relationship diagram

These diagrams starting with a central problem or a central idea and show the influencing factors or causes and their relationship. When the diagram is being developed, the possible causes are arranged as cards around the issue or problem. In the second step, cause and effect relationships between the cards are shown, thus revealing possible principle causes. The relationship diagram is suitable for the visualization of complex thought processes.`

Tree diagram

In an extension of functional analysis, the tree diagram describes relationships between targets and the measures needed to achieve them Starting from the target under examination, possible solutions are shown as branches to the right. Each solution identified is then investigated in order to determine whether it represents an activity which can be executed directly. When this is not the case, the appropriate branch must be branched out more widely.

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Matrix diagram

A matrix diagram shows relationships and interactions between two factors. These diagrams are usually used to link two lists. A typical application for this mode of representation is the House of Quality used in GFD.

Portfolio (Matrix data analysis)

Matrix data analysis helps to reveal the hidden structure of a jumbled mass of information. The information recorded in a matrix diagram can be investigated in greater detail on the basis of defined criteria or dimensions in a portfolio.

Problem decision plan

The problem or process decision plan is used to recognize potential problems at the planning phase and to develop preventive measures. Starting from the target specified, the points which are important to the success of the operation are discussed and investigated with a view to identifying possible problems and weighting them. Counter measures must be developed for the items which have been prioritized.

Network diagram

Network or arrow diagrams are suitable for presenting individual operations in a project and their dependencies. The sequence is shown by operations to be conducted either sequentially or parallel to one another.