Last Updated on 9 September 2023
Also known as cause and effect diagram, herringbone, Ishikawa and Fishikawa, Fishbone Diagrams are for getting to the underlying causes of an effect you are seeing. They can be used to identify the issues causing a problem, or the components that you need to consider to have the result you want.
They take the form of a large fish bone, with the main line being the issue, and each large branch being a line of inquiry into the causes.
The are also known as Ishikawa diagrams after Dr Kaoru Ishikawa who developed them in Japan and made them well used, and ‘cause and effect diagrams’, as it is trying to uncover the ‘causes’ of the ‘effects’ we are seeing.
They are like 5 whys in that they get deep into the issue to find out the real reasons for the problem, but it has the advantage that it can give you a large number of root causes, whereas 5 whys will only take you down one path.
When do you use fishbone diagrams?
Fishbone diagrams are very versatile, and so are used throughout the Six Sigma projects. The main use though is during the analyze phase of DMAIC when trying to get to the root cause of an issue, and can often be very helpful at the start of analyze, when you’re trying to find which way you should focus your attention. They are for when you think there may be multiple root causes, or you want to explore all possibilities; for simpler problems you have 5 whys analysis.
They can often be used after a brainstorming exercise to organize the ideas, or even alongside it to help stimulate new ideas. It is essentially a well structured form of brainstorming, so can be helpful if you’re not getting the answers you need.
It is useful any time you want to find the major root causes of an issue or find solutions to a problem.
How to create a fishbone diagram
- Draw a line across your paper through the middle lengthways
- Write your issue that you want to analyze in a box to the right of the line. This makes the ‘head’ of the fishbone.
- Draw a branch (sub-bone) away from the long line for each key component or key cause to investigate. If you’re struggling for ideas on these there are standard examples below
- Draw a smaller ‘bone’ away from these branches for the sub-cause (cause of the cause)
- Keep adding branches until it stops adding helpful analysis
Make sure you don’t stop too early, as if you do stop before you get to the root cause you may be fixing a symptom not the actual issue. It may be worth actually doing 5 whys analysis on each issue on the chart as you fill it in in order to make sure you’ve been thorough enough.
Agree with the team which are the main root causes. You can use multivoting to help you with this.
A fishbone diagram is usually based on the opinions of the team, and so will give you a ‘best guess’ or working theory of the solution(s). The final stage is therefore to investigate and verify the root causes you’ve found before you start to tackle them.
Some standard formats to get you started
The different branches should show the main issues / focuses at play in the process. It can be hard to identify these, as there are so many potential categories to choose from.
If you’re floundering about (sorry) for where to start there are standard ones for some areas that can give you a head start when you’re staring at a blank sheet of paper. Be careful not to let them stop you finding your own ideas, as you may miss a major branch.
Often used in manufacturing, this is the one that you’ll see most frequently.
- Manpower – staff members including training, morale issues etc.
- Materials – the inputs (consumables) that are used in your process; this can be raw material or data depending in the type of process
- Machines – equipment that is used in the process (non-consumables), which can include computers, machinery and vehicles
- Methods – processes and procedures that you follow in the job
- Measurement – mostly methods used in quality control and measuring quantities
There is a 6th M that is often used to make it 6 M’s:
- ‘Mother Nature’ – the environment that the work is carried out in, and facilities around the area.
Other ones you can use are:
- 7 P’s (common in Marketing) – Product, Price, Place, Promotion, People, Process, Physical Evidence
- 5 S’s (useful for service organizations) – Suppliers, Surroundings, Systems, Skills, Safety
- 5 W’s – Who, What, When, Where, Why (you can tell from my standard page structure that I’m a big fan of this one!)
- 4 P’s – Policies, Procedures, People, Plant
Start from these categories, and then you can do ‘5 whys’ starting with ‘why is x the issue’, ‘what is wrong with x’ or ‘why is x important’, whatever you’re trying to work out.
Alternatively, you can create your own that are most applicable to the issue being looked at.
An example for me analyzing why I was late for work.
I’ve used key factors that I think were the main issues, namely:
- I was tired which slowed me down
- It took me longer than usual to get ready
- Commute took a long time
As you can see, each issue is broken down into its sub issues, and those are broken down further, until you can find all the core issues that led to me being late for work. These are now easily identifiable and can be worked upon.
It’s obvious from the graph that even 5 whys is not always enough to get to the root cause – why did the air conditioning miss its service? Don’t stop your analysis until you’ve got a root cause that can be worked on, or you’ll not fix the actual issue.
The issues can also be used to populate your check sheet for data collection.