The benefits of Ishikawa diagrams can be summarized as follows: The different ideas generated by these people will often lead to a more complete picture of the causes actually present. This is why it is very important to get input from all individuals involved with the process. Of course, the main weakness of a diagram is that its accuracy depends on the person or group that draws it. By putting the problem on paper, everything becomes known and can be studied. Ishikawa diagrams graphically illustrate all the influencing factors of a problem. This keeps us focused on what we want to accomplish- minimizing the variation. We must then keep asking, “Why does the dispersion occur?” as we look at each variable on our diagram. This organizes the causes into categories that can be studied one at a time. Next, draw arrows to the branches and label them, detailing variability contributors. List the main groups that influence the problem by their general category - workers, materials, tools, inspection, and machinery. To make a dispersion analysis diagram, start with the problem on the right and draw an arrow to it, as shown in Figure 2.2.2. We may be able to eliminate most causes, or even add a few that were not described. When investigating the causes, we use the diagram to note progress. Later we might be able to combine the diagrams and organize the causes using some criterion, such as the cause’s relative importance, or the sequence of events. A good diagram will look extremely complicated and busy however, if everything is included on the chart, the true causes of the problem should be listed.įor a compound problem, several diagrams may be necessary. It is important to list all possible causes put down everything that comes to mind. Along the stem of the arrow draw smaller arrows and label them with the possible causes. To create a cause enumeration diagram, first put the problem on the extreme right side of the page, as in Figure 2.2.1. The dispersion analysis and process analysis diagrams are derivatives of the basic cause enumeration diagram, and they are used to highlight process control problems. Process analysis diagram - A flow diagram used to study quality problems.Dispersion analysis diagram - A diagram used to analyze the causes of variability in a process.Cause enumeration diagram - A graphic diagram used to list all the possible causes of a problem.There are three types of cause-and-effect diagrams: Diagrams organize thinking and provide a plan of attack. Making a diagram is possibly the best first step in analyzing a problem prior to data collection. A cause-and-effect diagram is a simple technique for dissecting a problem or process. A more complete explanation of these diagrams can be found in his book, Guide to Quality Control, 1976.
Kaoru Ishikawa (1915-1989), a noted Japanese authority on quality and productivity, developed these diagrams for problem-solving.