ishikawa diagram definition

This is an excerpt from the book "Five Minute Lean", by David McLachlan - a wonderful book that blends teaching of the tools, culture and philosophy of traditional Lean with a modern-day Lean parable.

You can get the whole book on Amazon here and enjoy your own copy.

Solve the Real Cause of the Problem

‘Using a Fishbone diagram and the 5 Whys is a fast and easy way to get to, and solve, the real cause of a problem.’

Implementing solutions to problems in our job or business often takes time and money to do. Many people spend this time and money only to discover they were solving the wrong thing – addressing only the symptoms and not the actual cause. Using the power of Root Cause Analysis can help us discover and solve the real problem and avoid this waste. Problems are also wonderful opportunities – if we can solve the real problem it can make our job easier and far more enjoyable.

When we have a specific problem that we need to solve, it is extremely important that we:

Clearly define the problem we are working on, before we begin.

This means we “go and see” the problem, directly where the work is done (at the Gemba, 2.2) and hopefully as soon as it happens (with Jidoka, 4.2).

It also means articulating the problem specifically as a gap from where we are to where we want to be, based on something measurable like our customer driven metrics (Quality, Delivery, Cost or Sales, 1.2) or reducing one or more of the eight wastes (3.1).

For Lisa this might mean reducing wait time in a queue from 10 minutes (where she is) to five minutes (where she wants to be) instead of just saying “less queue time”. Defining a problem in this way also makes it easy to know when you have succeeded – you are not chasing a vague concept. And because you have defined the problem as a measurable gap, it is also easier to present a clear view from the problem, to a solution.

During our Kaizen meetings, while mapping our process, or even when walking the Gemba, we may need to get to the real cause of these problems we reveal. To do so we use a Fishbone diagram and the “Five Whys”.

Fishbone or Ishikawa Analysis

A Fishbone diagram is used to get a quick idea of where the cause of our problem might lie by separating ideas into categories.

The four categories are:

People
Information
Process
System

An easy way to remember them is “PIPS”.

In Manufacturing, the four categories can also be known as the “Four M’s”: Man and woman, Materials, Method, or Machine.

To use a Fishbone diagram, Lisa would note her clearly defined problem at one end, the “head” of the fish. She could then have her team-mates call out reasons why they believe the problem is happening. These reasons would be noted under any of the four categories, depending on where the cause lies.

As usual, a picture says a thousand words:

fishbone diagram

Figure 15: An example of a Fishbone or Ishikawa diagram, noting reasons under People, Information, Process and Systems. Once complete, we can group similar problems or reasons together and then perform the Five Whys.

Once she had a few reasons, Lisa could group them together further. For example, there might be a few reasons that relate to how people are trained, or others that always come back to a certain department. This allows her to narrow down her causes effectively into one or two main reasons, and she can then delve even deeper with the Five Whys.

The Five Whys

Once we have an idea of where our problem lies using a Fishbone diagram, we can use the Five Whys to delve deeper into any of the main reasons that we have come up with, if we need to.

To perform the Five Whys, we ask “Why” this is happening, and with each new answer ask why again until the answers have been exhausted or we need to gather more data.

Let’s say that in one of the process steps at the Shoe Emporium Lisa identified that there is a high rework percentage, perhaps 50%. Maybe it’s a form that doesn’t get filled out correctly and needs to be re-done.

The conversation might go a little like this:

Why does the form come back for rework 50% of the time?

1. The customer doesn’t fill it out correctly

Why?

2. They don’t feel like they have to, or they don’t understand it

Why?

3. We haven’t explained the importance of the form or how to fill it out

Why?

4. We don’t focus on building in quality when gathering the information, and it is too easy to make a mistake.

In this scenario we didn’t need all five “whys” – this is OK. The main point is to keep asking until the answers have been exhausted, or we need more information. We also know our Five Whys are working when we can go back up the line of questions and replace “Why” with “Therefore”.

For example:

4. We don’t focus on building in quality when gathering information

Therefore:

3. We haven’t explained the importance of the form or how to fill it out

Therefore:

2. Our customers don’t understand it

Therefore:

1. Our customer doesn’t fill it out correctly and it comes back 50% of the time.

Once you have narrowed down your answers, you can add the real problems into your Value Stream Map as Kaizen Bursts, and brainstorm solutions with your team-mates.

When you are brainstorming solutions, you can use ideas from Chapters Three, Four and Five to help you. This will give you tools such as having a standard process, error proofing or stopping when a defect is found, working towards one-piece flow, then changing how people are measured or rewarded and making information, process steps, queue times or other things visible, which can all have a huge impact.

It is also a good idea to use the 5 Whys on our processes – as in “Why do we do this step?” In many cases a process may have been created long ago and things have changed or moved on, leaving the process unnecessary. If the only reason for doing something is because “this is the way it’s always been done,” then thank goodness you are going through a Lean transformation!

Selected chapters from the story within Five minute Lean:

Check out these selected chapters from the teachings within Five Minute Lean: