EWMA Chart with Minitab

What is an EWMA Chart?

The EWMA chart (Exponentially-Weighted Moving Average Chart) is a control chart monitoring the exponentially-weighted average of previous and present subgroup means. The more recent data get more weight than older data. It detects the shift of the process mean from the process target over time. The underlying distribution of the EWMA chart is normal distribution.

EWMA Chart Equations

Data Point:


Center Line:


Control Limits:



  • CumSum EQ is the mean of the ith subgroup
  • λ and k are user-defined parameters to calculate the EWMA data points and the control limits

Use Minitab to Plot an EWMA Chart

Data File: “EWMA” tab in “Sample Data.xlsx”

Steps in Minitab to plot EWMA charts:

  1. Click Stat → Control Charts → Time Weighted Charts → EWMA.
  2. A new window named “EWMA Chart” appears.
  3. Select “Gap” in the box below “All observations for a chart are in one column.”
  4. Select “Sample” as the “Subgroup sizes.”
  5. Enter “0.5” as “Weight of EWMA.”
  6. Click “OK.”
  7. The EWMA chart appears in the newly-generated window.

Model summary: One data point falls beyond the upper control limit and we conclude that the process is out of control. Further investigation is needed to discover the root cause for the outlier.

About Michael Parker

Michael Parker is the President and CEO of the Lean Sigma Corporation, a management consulting firm and online six sigma training, certification, and courseware provider. Michael has over 25 years of experience leading and executing lean six sigma programs and projects. As a Fortune 50 senior executive, Michael led oversight of project portfolios as large as 150 concurrent projects exceeding $100 million in annual capital expenditures. Michael has also managed multi-site operations with the accountability of over 250 quality assurance managers, analysts, and consultants. He is an economist by education, earning his Bachelor of Science degree from Radford University while also lettering four years as an NCAA Division I scholarship athlete. Michael earned his Six Sigma Master Black Belt certification from Bank of America and his Black Belt certification from R.R. Donnelley & Sons.

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