Cause & Effect – Fishbone Diagram

Find and cure causes not symptoms

Why Use It?

To allow a team to identify, explore and graphically display, in increasing detail, all of the possible causes related to a problem or condition to discover its root cause(s).

What does it do?

• Enables a team to focus on the content of the problem, not on the history of the problem or differing personal interests of team members.
• Creates a snapshot of the collective knowledge and consensus of a team around the problem. This builds support for the resulting solutions.
• Focuses the team on causes, not symptoms.

How to do it.

1. Select the most appropriate cause and effect format.

There are two major formats:

1. i.      Dispersion Analysis Type is constructed by placing individual causes within each “major” cause category and then asking of each individual cause “Why does this cause (dispersion) happen?” This question is repeated for the next level of detail until the team runs out of causes. The graphic examples shown in step 3 are based on this format.
2. ii.      Process Classification Type uses the major steps of the process in place of the major cause categories. The root cause questioning process is the same as the Dispersion Analysis Type.
3. Generate the causes needed to build a Cause & Effect Diagram. Choose one method:

• Brainstorming without previous preparation.
• Check Sheets based on data collected by team members before the meeting.

1. Construct the Cause & Effect/Fishbone Diagram
   1. Place the problem statement in a box on the righthand side of the writing surface.
      1. i.      Allow plenty of space. Use a flipchart sheet, or large white board.

Fishbone 1

Make sure the whole team agrees on the problem statement. Include as much information as possible on the “what,” Where,” “when,” and “how much” of the problem. Use data specify the problem.

1. Draw major cause categories or steps in the production or service process. Connect them to the “backbone” of the fishbone chart.

Fishbone 2

Illustration note: In a Process Classification Type format, replace the major “bone” categories with: “Order taking”, “Preparation”, “Cooking” and “Delivery”

1. Be flexible in the major cause “bones” that are used. In a production process the traditional categories are: Machines (equipment), Methods (how work is done), Materials (components or raw materials), and People (the human element). In a service process the traditional methods are : Policies (higher-level decisions rules), Procedures (steps in the task). Plant (equipment and space), and People. In both types of processes, Environment (buildings, logistics, and space), and Measurement (calibration and data collection) are also frequently used. – There is no perfect set or number of categories. Make them fit the problem.

Fishbone 3

1. Place the brainstormed or data-based causes in the appropriate category.
   1. i.      In brainstorming, possible causes can be placed in a major cause category as each is generated, or only after the entire list has been created. Either works well but brainstorming the whole list first maintains the creative flow of ideas without being constrained by the major cause categories or where the ideas fit in each “bone”.
   2. ii.      Some causes seem to fit in more than one category. Ideally each cause should be in only one category, but some of the “people” causes may legitimately belong in two places. Place them in both categories and see how they work out in the end.
2. Ask repeatedly of each cause listed on the “bones” either:
   1. i.      Why does it happen?
   2. ii.      What could happen?
3. Interpret or test for root cause(s) by one or more of the following:
   1. i.      Look for causes thatappear repeatedly within or across major cause categories.
   2. ii.      Select through either an unstructured consensus process process or one that is structured, such as Nominal Group Technique or Multivoting.
   3. iii.      Gather data through check Sheets or other formats to determine the relative frequencies of the different causes.
   

   Fishbone 4