| It is difficult if not impossible to solve complicated | | | | - Sort the list by grouping causes that are related. |
| problems without considering many factors and the | | | | - Identify or name each major grouping and make your |
| cause-and-effect relationships between those factors. | | | | cause-and-effect diagram. |
| Defining and displaying those relationships helps. The | | | | - Machine, Manpower, Material, Measurement, Method |
| first such cause-and-effect diagram was used by | | | | and Environment are frequently used major causes |
| Kaoru Ishikawa in 1943 to explain to a group of | | | | that can apply to many processes. |
| engineers at the Kawasaki Steel Works how various | | | | The advantage of the cause enumeration technique is |
| work factors could be sorted and related. In recognition | | | | that you stand a much better chance that all causes |
| of this, these diagrams sometimes are called Ishikawa | | | | will be listed, especially hidden ones, and your diagram |
| diagrams. They are also called fishbone diagrams, | | | | will be a complete and useful picture. The |
| because they look something like fish skeletons. | | | | disadvantage is that it may be difficult to relate all the |
| What can it do for you? | | | | causes clearly to the result, making the diagram hard |
| Quality problems are typically not simple. They often | | | | to draw. |
| involve the complex interaction of several causes. A | | | | Variation 2: Process Classification |
| cause-and-effect diagram will help you: | | | | Sometimes it is more helpful to look at causes in the |
| - Define and display the major causes, sub-causes and | | | | sequence in which they occur instead of considering |
| root causes that influence a process or a | | | | overreaching logical categories. With this approach, the |
| characteristic. | | | | center line or backbone follows the sequence of the |
| - Provide a focus for discussion and consensus. | | | | process. |
| - Visualize the possible relationships between causes | | | | - Instead of primary causes as the ribs, show the |
| which may be creating problems or defects. | | | | major process steps from left to right. |
| Cause-and-effect diagrams are particularly useful in | | | | - Construct your cause-and-effect diagram as before. |
| the measure and improve phases of Lean Six Sigma | | | | The advantage of this technique is that, since it follows |
| methodology. | | | | the sequence of the process, it will be easy for |
| How do you do it? | | | | everyone to understand. The disadvantages are that |
| | | | similar causes will appear again and again, and causes |
| 1. Decide which quality characteristic, outcome or | | | | due to a combination of factors will be difficult to show. |
| effect you want to examine. You might consider | | | | Hints for Making Good Diagrams |
| Pareto analysis to help you focus on the most | | | | |
| important issue. | | | | 1. Get input from many people involved in the process. |
| 2. Write your chosen effect on the right side of a | | | | Not only will this make for a more accurate diagram, |
| paper, board or flipchart and draw a box around it. If | | | | everyone taking part will gain new knowledge. |
| you think of this as a fishbone diagram, this is the fish | | | | 2. Make one cause-and-effect diagram for each |
| head. | | | | Critical-To-Quality (CTQ) characteristic you are |
| 3. Draw a straight line to the left, the fish backbone. | | | | considering. Trying to include all CTQs on one diagram |
| 4. For each primary cause or category of causes, | | | | will make it too large and complicated to be of much |
| draw a diagonal line slanting from left to the centerline. | | | | use as a problem solving tool. |
| Alternate these ribs on the top and bottom of the | | | | 3. Avoid generalities. Express each cause as |
| backbone. Label the end of each rib and draw a box | | | | concretely as possible. |
| around the label. | | | | 4. Since you will use your diagram to direct the |
| 5. Draw a horizontal line intersecting the appropriate | | | | examination of specific cause-and-effect relationships |
| diagonal line and label it to describe each secondary | | | | with data, the characteristic you are considering and all |
| cause that influences a primary cause. Alternate these | | | | the causal factors should be measurable. If they are |
| medium sized bones to the left and right of each rib. | | | | not, try to make them measurable or find substitutes. |
| 6. In a similar way, draw and label diagonal lines for | | | | 5. The objective of the cause-and-effect diagram is |
| third level or root causes, small bones, intersecting the | | | | action. Be sure your causes are broken down to the |
| secondary cause lines, medium sized bones. | | | | level at which they can be acted on. |
| 7. Examine the diagram. If certain causes seem to | | | | Now what? |
| have a significant effect on the characteristic you are | | | | · Use your diagram to develop a common |
| examining, mark them in a special way. | | | | understanding of the factors potentially influencing or |
| Variation 1: Cause Enumeration | | | | causing a quality problem. |
| Sometime it may be very difficult to determine the | | | | · Use your diagram as a road map for |
| primary causes to be included in your diagram. If that is | | | | collecting data to verify the causal relationship of |
| the case, after you have determined the characteristic | | | | various factors to the characteristic. |
| or effect you are examining, follow these steps: | | | | · Continue to annotate and modify your |
| - Use brainstorming to create a list of all the possible | | | | diagram as you verify relationships and learn more. |
| causes. The list will contain a mixture of primary, | | | | Using a cause-and-effect diagram this way will help |
| secondary and tertiary (or big bone, middle sized bone | | | | you to see which factors in your process need to be |
| and small bone) causes. | | | | checked, modified or eliminated. |