Using the Fishbone Diagram for Quality Control

Defining and Isolating Problems

The purpose of the “fishbone diagram” (developed by Japanese quality expert Dr. Kaoru Ishikawa) is to understand processes and the outcomes of those processes. Usually, it is used to isolate weaknesses and problems within processes, but the method can also be utilized to initially design processes. It divides different process aspects into various classifications and examines how they interrelate with one another.

Developing the diagram

The fishbone diagram assumes that all processes are known. Diagramming starts with a well‐focused challenge, problem, or goal; this is listed at the right and a line is drawn to the left with an arrow pointing to the final goal. The primary question is “Why is it happening?” (in the case of processes already in place) or “How can we make this happen?” (in the case of new processes being put into place). One examines the details and processes that go into that goal on lines intersecting with the main line. Then, one examines the processes that go into the lines just drawn, gradually going into greater detail. As one gets into the process, every once in a while it is useful to step back and determine if this represents a reasonable model of processes as they now exist and/or processes that need to be put into place. If more detail is needed fill it in. Alternatively, if some aspect is irrelevant, it can be crossed off.

This can be done as a group exercise among managers, with the lines drawn on a whiteboard by the group leader. Once the diagram is finished, copies should be made for all those involved with making the final decisions. Notes can then be made on them for later discussion.

The major goal of drawing a fishbone is to determine cause and effect for the different processes. Once one understands the processes, actions that directly address the problems can be taken.

Figure 1 shows a typical fishbone diagram in which different quality control measurements are used with the final goal being a quality roasted coffee product.

Evaluating the Fishbone

Once the fishbone has been drawn with the relevant processes in place, one can go deeper into the processes to examine any challenges that exist or might be anticipated. In the numerous articles available, these are listed as the “6 M’s, 5P’s, and 4 S’s, with different disciplines (manufacturing, services and marketing) having developed their own set of evaluation criteria. For a coffee roasting plant, the processes that seem most important include:

• People
• Methods
• Materials
• Procedures
• Machinery
• Environment
• Measurements

People (personnel) evaluation: At each point, it should be determined who is responsible for successfully completing each aspect. The person assigned should (1) have the necessary skills to perform the task, (2) have adequate time to perform the task, and (3) be able to perform the task in a timely manner so that the process can proceed. Is adequate manpower being provided to successfully complete the task? Is training possible? Can some functions be successfully combined for efficiency? Can third party testing be effectively and efficiently utilized?

Methods and procedures (systems evaluation): The question here is if each aspect of the process is understood by both management and the individual who performs the task. Are there places on the diagram that are often problematic or where more quality control needs to take place? If so, what is needed (testing more often, investment in testing equipment, training) to correct the situation?

The individual methods now in use should also be considered. Could these methods be written down formally as in a manual? Are the same methods in use throughout the system? Do the methods employed flow naturally from one area to another? If a database system is being contemplated or in place, what are the areas where data collection and evaluation would be most useful?

Materials: Would sourcing new materials or sources of materials (such as green beans, teas, etc.) be helpful?

Machinery: Are there areas where investment in better (faster operation, higher quality, greater capacity) machinery can assist in streamlining a process or getting better outcomes?

Environment: Are there plant design aspects, such as relocation of storage or machinery that would make certain tasks easier? Are there improvements to the comfort of the environment that would make tasks easier? Is relocating or expanding the production plant itself needed?

Measurements: Measurements put a number to what is to be accomplished. Are there general policies that should be put into place to guarantee an outcome? An example would be “cup every roast” or “cup at least 9 cups of every green lot received”. There may be some areas where more quality control is necessary; usually packaging requires a lot of testing to maintain a reasonable standard. One must also define a reasonable rate of anticipated failure (example: only 5% of packages can contain more than 2% oxygen) and a reasonable range of testing (the Agtron roast color measurement should be between 50 and 54).

Once this has been well considered by the management team members, a meeting takes place in which the fishbone is reconsidered and revised if necessary. In examining the finished diagram, determine priorities: which are the most important actions to be taken? One can rate each process as “1” (of primary importance, “2” (an important contributor but not vital), and “3” (unsure or not a major factor in what is being considered). Are there some steps that can be taken quickly and easily? What investments will need to be made (in new equipment, additional personnel, or training of existing personnel)?

Finally, an action plan is determined. This plan should have definite work assignments and responsibilities, dates by which certain steps should be taken, and a time when the team will meet to follow up. All materials generated by the team should be retained for later evaluation.

The purpose of the fishbone diagram is to examine how to achieve a specific goal or how to correct a problem. This is done by a careful and systematic examination of all of the causes that lead to the effects. It is useful in determining what can be accomplished in a large and interrelated system of processes.

Once the effort and time has been spent to develop the diagrams and action plans, follow up becomes of major importance. Action plans may need to be revised and one may develop a different view of the processes over time, but usually even performing the analysis results in considerable insight that should not be disregarded. Successful quality control programs are only achieved when realistic and well thought out programs that directly address quality features of the product are put into place.

Summary

The fishbone diagram is a pictorial view of a process that can be developed to look into the details of cause and effect. It is useful in quality control programs to examine the causes of problems in quality that occur or putting new procedures into place. This is done as a team exercise among managers and often includes a third party with experience in quality control and coffee to lead the group.

©2013, Songer and Associates, Inc.