Creative Combination

3 tools to jump-start a lean Six Sigma project

by Scott Force

This article was featured in January 2016’s Best Of Back to Basics edition.

Since 2002, I have been facilitating lean Six Sigma projects and coaching other belts through their projects. Combining tools is a technique I use with teams when potential root cause analysis through a fishbone diagram does not show any obvious direction.

Fishbone diagram

From using the fishbone diagram, most quality professionals know there are usually three outcomes:

  1. One of the bones in the diagram is full of potential causes, leading a team to focus on a particular area (Figure 1).
  2. The same potential root causes appear in several bones of the diagram, indicating a systemic cause that, if eliminated, will address several areas of concern (see Online Figure 1).
  3. No common cause is seen throughout the diagram, and all bones show several potential causes (Online Figure 2).

Figure 1

In the first two cases, the team has some direction by strategically focusing on the particular bone, shown by the circle in Figure 1, or the recurring systemic causes showing up in multiple locations, shown in Online Figure 1. But what do we do in the case of Online Figure 2?

Online Figure 1

Online Figure 2

By combining the completed fishbone diagram with two other tools from our Six Sigma tool kit, we can take a strategic approach to proceed.

SIPOC diagram

Using a suppliers, inputs, process, outputs and customers (SIPOC) diagram, map the high-level flow for the process to which the fishbone diagram is tied. The key items we will use from this tool are the list of outputs (Online Figure 3).

Online Figure 3

Cause and effect matrix

The cause and effect matrix shown in Online Table 1 is what ties together the outputs of the fishbone diagram with the outputs from the SIPOC diagram. Part of the quality function deployment house of quality, the cause and effect matrix is the center section of the house and is also known as a relationship matrix.

Online Table 1

The details of completing a cause and effect matrix are beyond the scope of this column. But the basic process uses a cross-multiplication method in which each row and column intersection is scored by the team for the degree of relationship and is multiplied with a rating of importance provided by the customer. Each of these multiplications is added across the horizontal row, providing the final score at the far right.

Putting the causes from a fishbone on the left side of the matrix and the outputs from the SIPOC diagram along the top allows teams to rate the relationship each cause has with each output, helping to rank and prioritize potential causes the team should investigate first. 

A completed cause and effect matrix is shown in Online Table 2. The top portion shows the outputs from a SIPOC diagram for making a hamburger. The left side shows the results of a fishbone diagram. In this example, only main causes are shown, but it is recommended that a team use the five whys and display the lowest-level causes on the diagram.

Online Table 2

In this generic example, overcooking the hamburger has the greatest relationship with our SIPOC outputs, indicating the team should focus on that cause first.   

Tool teamwork

While the SIPOC diagram focuses on desired outcomes and the fishbone diagram focuses on the undesired causes of a problem, creatively combining these tools provides the team with more options on how to proceed with the project.

As a lean Six Sigma practitioner, you should begin to see how many of the tools and techniques naturally work together to provide a more focused approach on process improvement.

Scott Force is a Six Sigma Master Black Belt trained by Sigma Breakthrough Technologies Inc. with more than 20 years of quality improvement experience in the healthcare, automotive and power equipment industries. He earned a bachelor’s degree in manufacturing engineering from Miami University in Oxford, OH. A senior member of ASQ, Force is an ASQ-certified quality technician, engineer and Six Sigma Black Belt.

it is a good idea to combine multiple quality tools
but an engineering assessment of weighted importance of factors might be more logical, more important than a customer`s weighted importance of factors, because the customers might not have a clue of the product, processes, etc.

Aylin N. M.

--Aylin N. Minikus, 11-27-2018

Will revise our workshop material to this approach of combining all 3 tools.
--CF Lee, 06-07-2014

--NS Pillai, 08-03-2012

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