Introduction To Total Quality Management

Introduction:

The cause-and-effect diagram is also called an Ishikawa diagram. Cause-and-effect diagrams can be extremely useful tools for hypothesizing about the causes of quality defects and problems. The Pareto diagram, which is used in connection with data analysis, can only be used to the extent that data exists on the problems or causes.

Cause-and-effect diagram

There are now six main causes in the diagram. 

• Whether any of the six causes can be left out must be determined separately in each specific problem situation.
•  
• Identification of the main causes is carried out through a series of data analyses in which the other quality tools (stratification, check sheets etc.) may be extremely useful when hard data are collected. Some situations call for the
• use of more advanced statistical methods, e.g. design of experiments or when soft data are used the so-called ‘seven new management tools’.

                                                                                                                         Fig: A cause-and-effect diagram showing the most common main causes of a given problem

Example of the Pareto Analysis:

•  Problem A (=cause A) has consumed by far the most working time and more than the other three problems together.
• It is therefore decided to ‘attack’ this problem first and a method is found to control A. After one rotation of the Deming Circle (Plan-Do-Check-Act), a new Pareto diagram can be constructed.

Fig: An example of the use of a Pareto diagram before and after the implementation of a preventive method

If a problem has many causes, which is often the case, then it can be necessary to construct a cause-and-effect diagram to show in more detail exactly which causes underlie the given problem. The Pareto diagram can therefore be used both at the problem level and the cause level. This can be extremely useful in connection with step 4 of the Deming Circle, i.e. in connection with the analysis of causes. The Pareto diagram, which is used in connection with data analysis, can only be used to the extent that data exists on the problems or causes.

1. Quality planning should therefore also take account of the data which are expected to be used in the subsequent data and causal analyses.
2. Since, as previously mentioned, the cause-and-effect diagram is basically a hypothesis of the connection between the plotted causes and the stated problem, then it should also be used in the planning of which data to collect.