Monday 5 November 2012

Debugging With Six Sigma Ishikawa

Back in September 2009 (that seems so long ago!) I wrote an article on problem solving using the 5 Whys technique. Some correspondents suggested that 5 Whys was a trivial/obvious technique, but they were missing the point somewhat - sometimes we overlook the obvious and need reminding of it, and sometimes the simplest techniques can provide the most valuable results.

That said, no one technique is guaranteed to work in all circumstances, so I thought I'd offer another technique that I use quite frequently: Ishikawa Diagrams, another part of the Six Sigma tool kit. They're sometimes known as cause-and-effect diagrams or herringbone diagrams. Again, they appear simplistic; and once again, I say beware of dismissing the simple and obvious! As with 5 Whys, the interaction between the people using the technique is perhaps the heart of the process, but the process guides and facilitates the discussion and discovery of information. Like 5 Whys, Ishikawa diagrams will help you to get to the root cause of your issue.

To use an Ishikawa diagram:

A) Determine a clear, brief description of the issue. Write it at the head of the fish bone skeleton, on the end of the spine

B) Decide the major categories for causes and create the ribs of the skeleton, writing one category at the end of each rib bone. These vary depending upon the industry and the situation in which the Ishikawa diagram will be used. I generally use a variation of the 6 Ms (used in manufacturing industries):

MDescriptionRecommendation for SAS
MachineEquipment / TechnologyHardware or software
Method ProcessProcess
Material Includes Raw Material, Consumables and InformationData
Man Power Physical work / Mind Power (brain work)People
Measurement InspectionInspection
Mother Nature EnvironmentEnvironment (physical or logical)

C) Now challenge the assembled group to contribute possible causes under each of the major categories. There are many ways to do this, such as by brainstorming or by asking each person to contribute one suggestion for each major category. Place each suggestion alongside the associated rib. As with mind-mapping, you might want to divide and sub-divide your suggestions. Remember, at this stage we're looking for potential causes, not solutions

D) Now review the diagram. Remove any suggestions which clearly don't apply to the specific issue at-hand, and try to garner further suggestions for categories where there are fewer suggestions. To drive down to the root cause, it may be appropriate to adopt a 5 Why approach for each suggestion

E) Discuss the diagram and agree the causes that you all think are the most likely to be at the root of the issue. It's okay to rely on experience and instincts at this point

F) Finally, develop plans to confirm that the potential causes are the actual cause. It is important to concentrate on proving the root cause before taking action to resolve the issue

Ishikawa diagrams are a great way to engage all participants and get a balanced list of ideas. They provide structure for any review session, and they encourage participants to push beyond symptoms to uncover potential root causes. However, you'll get the best results if you have a precise problem definition at the start of the review session.

If you look carefully, you can find tools for drawing nice, neat Ishikawa diagrams but, in my opinion, you can't beat getting a group of people armed with marker pens and sat around a whiteboard or drawing board. The human interaction is an important part of the process.

First documented by Kaoru Ishikawa in the late 1960s, Ishikawa diagrams are a firm part of many sets of practices including Six Sigma and ITIL. Highly recommended.