Importance of Measurement Systems Analysis
Measurement Systems analysis is an integral part of the Six Sigma project. No matter what project is being conducted under the Six Sigma methodology, this part of the process can never be omitted out and the successful results still be obtained. Below is an explanation about what makes Measurement Systems Analysis such an integral part […]
What is Aggregate Planning? – Importance and its Strategies
Introduction An organization can finalize its business plans on the recommendation of demand forecast. Once business plans are ready, an organization can do backward working from the final sales unit to raw materials required. Thus annual and quarterly plans are broken down into labor, raw material, working capital, etc. requirements over a medium-range period (6 […]
Selecting 3PL Service Provider for Warehouse Management
Global business models are rapidly changing. Shorter life cycles of products and new business need exert pressure on Supply Chain managers to keep pace with the new scenarios. They are often faced with the target to reduce logistical costs and establish new supply networks. It has now become a common practice to outsource all logistical […]
The Impact of GDPR on Business
The Internet has drastically changed in the past few years. Consumers have now become very aware of their privacy issues. Many consumers want to be in control of the data that they create and share online. Till now, the contracts used to be drawn by social media companies. Hence, they were heavily skewed to be […]
Effective Product Design
Introduction Organization success is dependent on customer satisfaction and delight. Customer satisfaction is achieved through development of product and service, which have all attributes required by the customer. A success product or services do not only have attractive package design but should be also able to provide robust performance. Thus, product design must be practical […]
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.
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Step 3B: Choosing the Correct Control Chart (Continuous Data)
February 12, 2025
