Control Charts vs. Six Sigma: Why the Discrepancy?

Control Charts vs. Six Sigma: Why the Discrepancy?

Have you ever wondered why Six Sigma and control charts appear to have conflicting goals? On the one hand, Six Sigma strives for processes to be as far away from the mean average as possible, while control charts aim to keep values within certain limits.

There is a crucial difference between the goals of Six Sigma and control charts. While Six Sigma aims to be as far away from the mean average as possible, control charts seek to keep results within certain limits.

Many people are familiar with Six Sigma and control charts regarding Lean Six Sigma or process improvement in general. However, the two have different goals for achieving process excellence. While Six Sigma strives for a process far from the mean average, a control chart seeks to keep a process within certain limits.

What is Lean Six Sigma?

Six Sigma is a set of techniques and tools used to improve the quality of products and services. It focuses on reducing the variation and defects in a process or development, increasing customer satisfaction. Six Sigma originates from the statistics involved, as Six Sigma refers to a standard deviation of 3.4 parts per million (ppm) away from the mean average. To achieve this, a process must be monitored, controlled, and improved continually. In addition, the Six Sigma methodology concentrates on reducing mistakes or errors.

Lean Six Sigma is a way of simplifying and scaling the improvement.?The Lean side of Lean Six Sigma has a strong focus on people and safety issues and concentrates on reducing or eliminating waste. Many articles claim that Lean Six Sigma is a blend, but in this author’s view, Lean Six Sigma is Six Sigma with a strong Lean influence.

What is a Control Chart?

A control chart is a graph used to monitor and evaluate data over time. It is a valuable tool for identifying trends, spotting outliers, and assessing data consistency. The chart typically consists of two lines: an upper control limit (UCL) and a lower control limit (LCL). Data points are plotted on the chart and compared to the UCL and LCL to assess whether the process performs within predetermined parameters. Control charts are used in many areas, such as quality control, manufacturing, process control, engineering, and finance.

How are they the Same?

?Control charts and Six Sigma calculations are tools for quality control and improvement. They are both based on the same principles of statistical process control.

Control charts and Six Sigma calculations measure the variation in a process over time. A control chart plots data points over time and highlights issues outside the established thresholds.

This allows you to see when there is a shift or trend in the process that needs to be addressed. Six Sigma calculations look at the overall process variability and can be used to identify opportunities for improvement.

Control charts and six sigma calculations are used to identify improvement opportunities and ensure that processes remain consistent and within an acceptable range of variation. Both techniques provide valuable insight into a process and can be used to ensure that operations stay in control and remain consistent over time.

?How do they Differ?

Six Sigma and control charts are two approaches to improving a process or system, and though they may have some similarities, the underlying philosophies behind them are different.

Six Sigma eliminates any variation from the desired outcome by moving as far away from the mean average as reasonable. At the same time, control charts seek to limit the deviation from the mean average by keeping it within certain limits. This means that Six Sigma mainly focuses on creating uniformity in a process, while control charts identify changes and trends in a process.

Six Sigma also encourages us to strive for perfection, whereas control charts provide an objective view of a process, helping us to identify any problems with it. Control charts can be part of a Six Sigma project, but Six Sigma takes a more systemic approach to improvement than simply monitoring a process’s performance.

?Ultimately, the most significant difference between Six Sigma and control charts is their goals: Six Sigma seeks to create total uniformity in a process, while control charts strive to keep variation within certain limits. By understanding this difference, we can better choose the approach that will help us improve our processes most effectively.

?Which is More Important?

When it comes to understanding which approach is more important, it depends on the type of situation you encounter. ?For example, Six Sigma focuses on eliminating variation and reducing defects, while control charts monitor and detect changes in process performance over time.

Six Sigma focuses on achieving and maintaining a high level of quality by reducing variability, while control charts provide information about trends in data. If your goal is to minimize defects and achieve high customer satisfaction, then Six Sigma is your better approach.

On the other hand, if you want to keep track of how well your process is performing and detect any changes in performance over time, then control charts would be more appropriate. Control charts can help identify changes in process performance and alert management when those changes occur.

Control charts and Six Sigma calculations are used to identify improvement opportunities and ensure that processes remain consistent and within an acceptable range of variation. Both techniques provide valuable insight into the process.

Overall, it’s essential to consider your goals and situation when choosing between Six Sigma and control charts. While both approaches have their place, one may be more appropriate for certain types of cases than the other.

Revised Article from Lean Six Sigma: International Standards and Global Guidelines, Second Edition by Terra Vanzant Stern, Ph.D. publishing 3rd edition in Summer of 2023.