Manufacturing ERP Software
Manufacturing Processes—Production and Business: The Interference Diagram, Part 1

Manufacturing Processes—Production and Business: The Interference Diagram, Part 1

By Bob Sproull

Review of Measurements for Effective Decision Making, Part 10

In my last post, I completed the Measurements for Effective Decision Making series. In it, I presented three throughput and performance measurement and reporting system reports:  throughput contribution report, buffer management report, and buffer hole percentage trend report.

Today’s post is Part 1 of a series on a very important improvement tool called the Interference Diagram. When used in conjunction with the Theory of Constraints, you will see that this tool is very helpful in identifying interferences that prolong the cycle time of a physical constraint.  Much of what I will present in this series is taken from one of my books, [1] Epiphanized—A Novel on Unifying Theory of Constraints, Lean, and Six Sigma, a book I co-authored with Bruce Nelson.

Introducing a high-utility tool with limitless applications

For those of us engaged in performance improvement initiatives, there seems to be a constant bombardment of “things” that interfere and prevent us from accomplishing our objectives. Some of these things come out of nowhere to stifle our efforts and still others are there just waiting to be found and acted upon. Wouldn’t it be great if there was a tool to help visualize these “things” so that we could do something about them? Life would be so much easier if we could eliminate these interferences before they become persistent problems, wouldn’t it? Good news, such tool already exists and it can help us identify and solve the myriad business and production challenges that face manufacturers every day. This tool is appropriately named the Interference Diagram (ID).

Most of you have probably never seen or even heard of an Interference Diagram (ID). Its origins date back to the mid-1990s with Bob Fox and the TOC Center in New Haven, Connecticut. As a thinking tool, it has not been well publicized. But don’t underestimate its utility. The endearing qualities of the ID are that it is simple to learn and construct, yet it is quite robust in its applications. The ID is a thinking tool that offers the capacity to define and visualize those interferences or obstacles that block or hinder your ability to achieve a specific goal or outcome. It is always far easier to define what we want, but much more difficult to define what stands in our way, and the ID helps us do that.

You have the “want” to change; now Identify the “what” to change

The ID can be used at many different organizational levels to understand why things don’t happen or work as they should. It can be used as a stand-alone tool or in conjunction with other tools. As a stand-alone tool, it provides a discrete analysis to better define and understand the obstacles that prevent accomplishment of our goal. In a broader application, it can be used to supplement the other, more common systems thinking tools developed by Dr. Eli Goldratt, developer of the Theory of Constraints, including his Five Focusing Steps. No matter how it is used, the results can be highly insightful and lead you to constructive change.

When the Interference Diagram was first drawn on whiteboards, it was not done to replace any of the available thinking tools, but to complete the analysis in less time. The ID is a thoughtful mind mapping tool that can quickly point a team in the right problem-solving direction. In essence, the ID was able to identify the “what(s)” to change. In initial applications, the “what” became a list of the many obstacles or interferences and not just a single core problem.

The biggest obstacle to solving a problem is to define the problem. If you are not sure what problem you are trying to solve, it is difficult to determine the correct solution. In other words, if you don’t know your destination, no path can get you there because you will never know when you have arrived. The ID structure and concepts are very simple, yet very powerful in helping to identify problems and solutions.

There are two basic ways to apply an Interference Diagram

The first application is using the ID as a thinking tool to exploit a known constraint. The second application involves using the ID in combination with the Intermediate Objectives (IO) Map/Goal Tree. This application offers a fast and highly effective way to develop an overall strategy and implementation plan. In my next post, I will present both types of applications.

Coming in the next post

Part 2 will further develop this new series on the Interference Diagram (ID).  As always, if you have any questions or comments about any of my posts, leave a message and I will respond.

Until next time.

Bob Sproull


[1] Epiphanized – A Novel on Unifying Theory of Constraints, Lean, and Six Sigma, 2nd edition, by Bob Sproull and Bruce Nelson, CRC Press, 2015.

Bob Sproull

About the author

Bob Sproull has helped businesses across the manufacturing spectrum improve their operations for more than 40 years.

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