X-Bar- and S-charts with Varying Subgroup Sizes Example

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Quality and Process Methods • Shewhart Control Charts • Additional Examples of the Control Chart Platform • X-Bar- and S-charts with Varying Subgroup Sizes Example

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The following example uses the Coating.jmp data table. This quality characteristic of interest is the Weight 2 column. An X-chart and an S chart for the process are shown in Figure 3.19.

Select Help > Sample Data Library and open Quality Control/Coating.jmp.

Select Analyze > Quality and Process > Control Chart > XBar.

Select the chart types of XBar and S.

Select Weight 2 and click Process.

Select Sample and click Sample Label.

The Sample Size option should automatically change to Sample Grouped by Sample Label.

Click OK.

Figure 3.19 X and S Charts for Varying Subgroup Sizes

Weight 2 has several missing values in the data, so you might notice the chart has uneven limits. Although, each sample has the same number of observations, samples 1, 3, 5, and 7 each have a missing value.

Note: When sample sizes are unequal, the Test options are grayed out. If the samples change while the chart is open and they become equally sized, and the zone and/or test option is selected, the zones and/or tests will be applied immediately and appear on the chart.

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Help created on 7/12/2018