Section 3 Control Charts
Lesson S03-01
Text: Section 3 pages 1 – 6
Duration: 23 minutes
Control charting can be done for both variable and attribute data types, but the mathematics involved depends on the data type. Furthermore, sample size considerations vary dramatically depending on whether the information is variable or attribute.
When the data is discrete, but the number of possible values is reasonably large, the data can be treated as variable type data. You may notice that in the first numeric example of this topic, the data is discrete (integer valued), but it will be handled as variable type data.
This topic mostly deals with variable type data but most of the concepts apply to attribute charts as well. The common charts for attribute data are discussed in Appendix II.
Recall that control limits are limits of expected variation. Hence, before attaining these limits, we must have a sense of what to expect. The question is, how much data is required before we have an idea of what to expect?
Introduction to Section 3 Control Charts
A quick overview of the section on control charts. An introduction to the process capability flowchart.
The Process Capability Flowchart
An introduction to the process capability flowchart.
An Overview of the Creation of  X̄ & R charts
Control charting can be done for both variable and attribute data types, but the mathematics involved depends on the data type. Furthermore, sample size considerations vary dramatically depending on whether the information is variable or attribute.
Once enough data has been collected, an estimate of the overall process average and the average range can be made. The estimates only have meaning if the process has been stable, so stability is assumed initially. If the process has not been stable, then we do not know what to expect, and there are no limits of expected variation.
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