I was recently meeting with one of Acuity Institute’s Lean Six Sigma Black Belt students. Her workplace project was heading into the measure phase and she was looking for some guidance on how to approach it. Our conversation led us to the formula Y=f(x), it is a cornerstone of the Lean Six Sigma methodology, and when you understand the application of this formula it can be very useful at every phase of your Lean Six Sigma DMAIC project.

A Closer Look at the Formula

Let’s begin with breaking down the components of the formula:

  • Y represents the outcome or output that you want.
  • X represents the various inputs or factors that are necessary to get the outcome. (There can be more than one possible X.)
  • F represents the function or process that will take the inputs and transform them into the desired outcome.

A simple way to explain this formula is that outcomes are the results of factors within a process.

Applying the Formula to the Phases of your Project

The goal of Lean Six Sigma is to understand the relationship between our various inputs (Xs) and the desired output (Y), so we can manipulate the Xs so that the outcome of the process (Y) is in the proper range and meets customer requirements.

This formula creates the foundation for your project. Let’s look at how the DMAIC roadmap and the formula Y=f(x) work together.

Define – In this phase, we identify the Y or outcome that we need to achieve and the desired customer expectations or CTQs. We also identify the potential Xs that are influencing the Y. Tools like the SIPOC or process maps can help us identify the potential Xs.

Measure – In this phase, we narrow down the list of potential Xs and measure the Xs and Y.

Analyze – In this phase, we test the relationship between each of the Xs and Y using graphical and statistical data analysis. This allows us to quantify which of the Xs have the strongest relationship, making them the most critical Xs and validating which Xs to take into the improve phase.

Improve – In this phase, we identify and possibly test the best solutions to implement that will address the critical Xs and improve the Y.

Control – In this phase, we establish the monitoring and response plans to ensure that the performance of the Y is maintained in the transition to the process owners and continues to be sustained over time.

The next time you are struggling with the next steps for your project, I encourage you to circle back to the Y=f(x) formula and see if it helps you to determine your next steps.

If you are looking to begin your journey as a Lean Six Sigma project leader, you may be considering which belt level is right for you. You can visit our website to learn more about Lean Six Sigma Green Belt or Lean Six Sigma Black Belt certification.

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