Process Capability and “Closing open windows”

I have an analogy that I like to use in class when teaching the concept of the Process Capability ppk analysis formula. The analogy is called “Closing Open Windows” and follows: I drive up to my house one July day when it is 105 degrees Fahrenheit outside. I can hear my condenser (my A/C’s external unit) humming…

I have an A/C unit that is rated for a house much larger than mine because I am not fond of the heat. When I enter my house, it is 98 degrees inside… Something is wrong. I check my thermostat and it reads 74 degrees. I check to make sure cold air is being pushed out through my vents. The cold air is effectively being diffused throughout the house. What is the next thing that you would investigate? Most answer that you should check for open doors and windows.

That is the obvious answer, but I often see “trained” Lean Six Sigma practitioners first knocking holes in the walls to see if they are missing insulation. They would first jump into a deep Root Cause Analysis without understanding the Current State Capability of the Inputs.

What is process capability?
What is process capability analysis?

“Jumping into the deep weeds”…

My team and I at Six Sigma Development Solutions, Inc. are engaged in LEAN and Lean and Six Sigma project work about 60% of the time. We encounter many different opportunities from a variety of disciplines. We are often called in to act as added capacity to an organization that has a Continuous Improvement system in place. When engaged with the teams at these organizations, I often witness them “jumping into the deep weeds” of Root Cause Analysis without understanding if the process is working as it was originally engineered to work. If it isn’t working, then where is the delta?

Process Capability ppk formula – Defining the inputs

The reason Six Sigma practitioners spend time meticulously defining the inputs into the process, in part, is to understand what we can measure. Those inputs with variable measurements potentially have tolerances. Those tolerances once understood to be the true “Voice of the Customer,” will then help us to understand the capability of the Current State of the Process Inputs. Once we understand both the Stability and Capability of each of the applicable inputs, this will help us to focus on those inputs with less capability. These inputs will potentially help us to understand the nature of the problem. All of this first depends on a trustworthy measurement system.

The principle of “Occam’s Razor”

The principle of “Occam’s Razor” says that often the simplest answer is the right one. Understand how the process was engineered to operate. Find manuals, SOP’s, FMEA’s and/or any other documentation. Call the Manufacturer of the machine or cell. Understand what the measurable inputs are in the process and understand their current state capability. Look for open windows first…

What are your thoughts?

Have you witnessed a team diving into a deep Root Cause Analysis in a Six Sigma project without first looking for open windows?