Step 3B: Choosing the Correct Control Chart (Continuous Data)
Just like there are many types of discrete data charts available, there are also many types of continuous control charts available. The Six Sigma process methodology prescribes which chart must be used when. The prescription in the case of continuous data points is largely based on sample size. Below is the list of the different…
Closing a Six Sigma Project
As we have seen, Six Sigma is an elaborate methodology. It requires time to learn and even more time to successfully implement. However, as we have also seen that there is a golden pot at the end of the rainbow. Countless organizations have transformed their operations based on their Six Sigma capabilities. Nowadays, having processes…
Conducting the Knowledge Transfer
The Six Sigma project is not complete until the concerned personnel who have to operate the process have the know-how to do so. Many Six Sigma projects have failed because the project team was overjoyed at achieving success. However, one must not forget that improvements are only on paper until they are implemented. And there…
If the data type that needs to be charted is discrete, then it must fall between one of binary or count types. As the name suggests in case of binary distribution, there are only two possibilities, success and failure, defective and not defective, whereas in the case of count type distribution there may be more than two possibilities of the process, the number of defects still need to be counted. The difference between the two is subtle. However, given the fact that there are fixed rules governing when which chart needs to be used, the confusion is reduced.
Equal Subgroup Size: In this case, the Six Sigma process methodology suggests using the C Chart. The C Chart counts the number of defects that are happening per unit of unit. This could be per minute, per hour, per day or per week and so on. The important part here is that since the time period is fixed, so is the sample size. The C Chart will tell you how many observations from a given sample failed to meet the criteria specified by the control limits.
Unequal Subgroup Size: In this case, the Six Sigma process methodology recommends using the “U” chart. The U chart counts the rate of defects. This means that it keeps a track of the number of units that it has monitored and how many have failed the given criteria specified by the control limits. The U Chart will tell you, for example that 5/1253 units have failed to comply. Hence it does not require a fixed time period or a fixed sample size and may be more convenient to use.
Equal Subgroup Size: In this case, the Six Sigma process methodology recommends using the NP Chart. The NP chart also counts the number of defects per period of time just like the C Chart. There is however a subtle difference between the two. C Chart is used when the occurrence of defects is rare. However, NP chart uses the binomial distribution. Therefore, the occurrences do not have to be rare. As a thumb rule, if there is a chance more than 5% defects in a process, then the NP chart must be used.
Unequal Subgroup Size: In this case, the P chart is recommended. Once again, it is quite similar to the U chart. This chart calculates the defects as a percentage figure meaning that it takes into account the units that have gone through the process just like the U Chart. The U chart also uses the Binomial distribution and is used when the occurrences of defects is not rare.
Article Written by
Himanshu Juneja, the founder of Management Study Guide (MSG), is a commerce graduate from Delhi University and an MBA holder from the esteemed Institute of Management Technology (IMT). He has always been someone deeply rooted in academic excellence and driven by a relentless desire to create value. Recently, he was honored with the “Most Aspiring Entrepreneur and Management Coach of 2025 (Blindwink Awards 2025)” award, a testament to his hard work, vision, and the value MSG continues to deliver to the global community.
Article Written by
Himanshu Juneja, the founder of Management Study Guide (MSG), is a commerce graduate from Delhi University and an MBA holder from the esteemed Institute of Management Technology (IMT). He has always been someone deeply rooted in academic excellence and driven by a relentless desire to create value. Recently, he was honored with the “Most Aspiring Entrepreneur and Management Coach of 2025 (Blindwink Awards 2025)” award, a testament to his hard work, vision, and the value MSG continues to deliver to the global community.
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Step 3B: Choosing the Correct Control Chart (Continuous Data)
April 3, 2025
