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Note that, as often happens, the final percentage is slightly different than 100%. This is due to round-off error and is nothing to worry about. The finished diagram is shown in Figure 8.8.

Figure 8.8. The completed Pareto diagram.

CAUSE AND EFFECT DIAGRAMS Process improvement involves taking action on the causes of variation. With most practical applications, the number of possible causes for any given problem can be huge. Dr. Kaoru Ishikawa developed a simple method of graphically displaying the causes of any given quality problem. His method is called by several names, the Ishikawa diagram, the fishbone diagram, and the cause and effect diagram. Cause and effect diagrams are tools that are used to organize and graphically display all of the knowledge a group has relating to a particular problem. Usually, the steps are: 1. Develop a £ow chart of the area to be improved. 2. De¢ne the problem to be solved. 3. Brainstorm to ¢nd all possible causes of the problem.

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4. 5.

Organize the brainstorming results in rational categories. Construct a cause and e¡ect diagram that accurately displays the relationships of all the data in each category. Once these steps are complete, constructing the cause and effect diagram is very simple. The steps are: 1. Draw a box on the far right-hand side of a large sheet of paper and draw a horizontal arrow that points to the box. Inside of the box, write the description of the problem you are trying to solve. 2. Write the names of the categories above and below the horizontal line. Think of these as branches from the main trunk of the tree. 3. Draw in the detailed cause data for each category. Think of these as limbs and twigs on the branches. A good cause and effect diagram will have many ‘‘twigs,’’ as shown in Figure 8.9. If your cause and effect diagram doesn’t have a lot of smaller branches and twigs, it shows that the understanding of the problem is superficial. Chances are you need the help of someone outside of your group to aid in the understanding, perhaps someone more closely associated with the problem. Cause and effect diagrams come in several basic types. The dispersion analysis type is created by repeatedly asking ‘‘why does this dispersion occur?’’ For example, we might want to know why all of our fresh peaches don’t have the same color. The production process class cause and effect diagram uses production processes as the main categories, or branches, of the diagram. The processes are shown joined by the horizontal line. Figure 8.10 is an example of this type of diagram. The cause enumeration cause and effect diagram simply displays all possible causes of a given problem grouped according to rational categories. This type of cause and effect diagram lends itself readily to the brainstorming approach we are using. Cause and effect diagrams have a number of uses. Creating the diagram is an education in itself. Organizing the knowledge of the group serves as a guide for discussion and frequently inspires more ideas. The cause and effect diagram, once created, acts as a record of your research. Simply record your tests and results as you proceed. If the true cause is found to be something that wasn’t on the original diagram, write it in. Finally, the cause and effect diagram is a display of your current level of understanding. It shows the existing level of technology as understood by the team. It is a good idea to post the cause and effect diagram in a prominent location for all to see. A variation of the basic cause and effect diagram, developed by Dr. Ryuji Fukuda of Japan, is cause and effect diagrams with the addition of cards, or CEDAC. The main difference is that the group gathers ideas outside of the

Figure 8.9. Cause and e¡ect diagram.

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Figure 8.10. Production process class cause and e¡ect diagram.

meeting room on small cards, as well as in group meetings. The cards also serve as a vehicle for gathering input from people who are not in the group; they can be distributed to anyone involved with the process. Often the cards provide more information than the brief entries on a standard cause and effect diagram. The cause and effect diagram is built by actually placing the cards on the branches.

7M TOOLS Since Dr. Shewhart launched modern quality control practice in 1931, the pace of change in recent years has been accelerating. The 7M tools are an example of the rapidly changing face of quality technology. While the traditional QC tools (Pareto analysis, control charts, etc.) are used in the analysis of quantitative data, the 7M tools apply to qualitative data as well. The ‘‘M’’ stands for Management, and the tools are focused on managing and planning quality improvement activities. In recognition of the planning emphasis, these tools are often referred to as the ‘‘7 MP’’ tools. This section will provide definitions of the 7M tools. The reader is referred to Mizuno (1988) for additional information on each of these techniques.

Affinity diagrams The word affinity means a ‘‘natural attraction’’ or kinship. The affinity diagram is a means of organizing ideas into meaningful categories by recognizing their underlying similarity. It is a means of data reduction in that it organizes a large number of qualitative inputs into a smaller number of major dimensions, constructs, or categories. The basic idea is that, while there are many variables, the variables are measuring a smaller number of important factors. For example,

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if patients are interviewed about their hospital experience they may say ‘‘the doctor was friendly,’’ ‘‘the doctor knew what she was doing,’’ and ‘‘the doctor kept me informed.’’ Each of these statements relates to a single thing, the doctor. Many times affinity diagrams are constructed using existing data, such as memos, drawings, surveys, letters, and so on. Ideas are sometimes generated in brainstorming sessions by teams. The technique works as follows: 1. Write the ideas on small pieces of paper (Post-itsTM or 3
5 cards work very well). 2. The team works in silence to arrange the ideas into separate categories. Silence is believed to help because the task involves pattern recognition and some research shows that for some people, particularly males, language processing involves the left side of the brain. Research also shows that left-brain thinking tends to be more linear, which is thought to inhibit creativity and pattern recognition. Thus, by working silently, the right brain is more involved in the task. To put an idea into a category a person simply picks up the Post-itTM and moves it. 3. The ¢nal groupings are then reviewed and discussed by the team. Usually, the grouping of ideas helps the team to develop a coherent plan. Affinity diagrams are useful for analysis of quality problems, defect data, customer complaints, survey results, etc. They can be used in conjunction with other techniques such as cause and effect diagrams or interrelationship digraphs (see below). Figure 8.11 is an example of an affinity diagram.

Tree diagrams Tree diagrams are used to break down or stratify ideas in progressively greater detail. The objective is to partition a big idea or problem into its smaller components. By doing this you will make the idea easier to understand, or the problem easier to solve. The basic idea behind this is that, at some level, a problem’s solution becomes relatively easy to find. Figure 8.12 shows an example of a tree diagram. Quality improvement would progress from the right-most portion of the tree diagram to the left-most. Another common usage of tree diagrams is to show the goal or objective on the left side and the means of accomplishing the goal, to the right.

Process decision program charts The process decision program chart (PDPC) is a technique designed to help prepare contingency plans. It is modeled after reliability engineering methods of failure mode, effects, and criticality analysis (FMECA) and fault tree analysis (see Chapter 16). The emphasis of PDPC is the impact of the ‘‘failures’’ (pro-

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Figure 8.11. Software development process a⁄nity diagram. From ‘‘Modern approaches to software quality improvement,’’ ¢gure 3, Australian Organization for Quality: Qualcon 90. Copyright # 1990 by Thomas Pyzdek.