There’s Something Fishy about Cause and Effect!

I always refer to Fishbone diagram as the most widely used Root Cause Analysis tool in the world today. That is a hefty title but, I can state this with confidence. The Fishbone diagram is definitely one of the Basic tools of Quality. The Fishbone Diagram was created by Kaoru Ishikawa in the 1960s, who pioneered quality management processes in the Kawasaki shipyards, and in the process became one of the founding fathers of modern management. 

Common uses of the Ishikawa diagram are product design and quality defect prevention, to identify potential factors causing an overall effect. Each cause or reason for imperfection is a source of variation. Causes are usually grouped into major categories to identify these sources of variation. The categories typically include:

• People: Anyone involved with the process
• Methods: How the process is performed and the specific requirements for doing it, such as policies, procedures, rules, regulations and laws
• Machines: Any equipment, computers, tools, etc. required to accomplish the job
• Materials: Raw materials, parts, pens, paper, etc. used to produce the final product
• Measurements: Data generated from the process that are used to evaluate its quality
• Environment: The conditions, such as location, time, temperature, and culture in which the process operates

(NOTE: The categories where derived by Dr. W.Edwards Deming. I consider measurement to be an output but Dr. Deming states, “The way we measure a process has an effect on the output..” from Out of the Crisis by Dr. W. Edwards Deming, 1982.)

How to create a Fishbone diagram:

Select the most appropriate cause & effect format. There are two major formats: 

The 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 of this tool section are based on this format. 

Cause and 

The 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. 

2. 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 

3. Construct the Cause & Effect/Fishbone Diagram. 

a) Place the problem statement in a box on the righthand side of the writing surface. 

Allow plenty of space. Use a flipchart sheet, butcher paper, or a large white board. A paper surface is preferred to allow the final Cause & Effect Diagram to be moved. 

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

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 decision rules), Procedures (steps in a 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. 

The example above uses the six most common major spines used in Quality Assurance diagnosing. 

c) Place the brainstormed or data-based causes in the appropriate category. 

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.” 

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. 

#If ideas are slow in coming, use the major cause categories as catalysts (e.g., “What in ‘materials’ is causing . . . ?”). 

d) Ask repeatedly of each cause listed on the “bones,” either: 

“Why does it happen “ For example, under “Securing hardware old”, this question would lead to more basic causes such as “missing straps”, “tools missing”, and so on.

Once you have exhausted all of the possible causes, the team will use another tools, which I will discuss on future blogs,  to help narrow the causes down to one, two or three that will be worked on to mitigate or eliminate. Most of the information on Root Cause Analysis comes from the Safety Management System Memory Jogger II written by Sol and Dennis Taboada. Available at dtitraining.com 


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