How to Create an Xbar-R Chart in Minitab 18
Why We Use XBar-R Charts
Before creating this type of chart you should consider other charts to display your data in. If you want to monitor the mean of your data, monitor its variation, and your data has subgroup sizes of 8 or less, this is the right chart for you. If you have 8 or more subgroup sizes in your data set, it’s better to use an X-bar-S chart. If there are no subgroups in your data, then you may want to consider an IMR-chart. In the event that your data is defective, then you should use an attribute control chart.
With the Xbar-R chart, you can monitor process stability over time and make corrections when necessary when the data seems to show trends or patterns. If nothing can be found wrong the process can be considered stable across all subgroups. Keep in mind that subgroups are the number of samples while sample sizes are the number of samples taken for each subgroup of samples.
You can download the Minitab file used in this tutorial to follow along here. Also, if you don't have the latest version of Minitab (18) you can download a trial for the new version here.
Add Data to Minitab
Input your data set into Minitab.
Chart Type Selection
Add your data to a chart by clicking Stat→Control Charts→Variable Charts for Subgroups→Xbar-R.
Set up the Chart
For this horizontally displayed data, choose "Observations for a subgroup in one row of columns" option. Select each subgroup in the box to the left and add them to the space to the right. This can be completed by highlighting each subgroup variable and clicking the select button.
Change Options
Click on Xbar-R Chart Options. Select all of the check boxes except for "stage" to display data in the table after the chart is created.
Display All Test Results
Next, choose the tests tab. From the dropdown menu choose "Perform all tests for special causes." Click the Ok button to exit Xbar-R chart options. This will display all test results possible.
Create a Title
Next, click on Xbar-R chart labels and the title "X-bar-R Chart for Hourly Samples," then click Ok. Now click on the Ok button within the Xbar-R Chart window to generate a graph.
Analysis
Saving Your Project And Exporting The Graph
To save you project click on the file menu and choose the save project option and save to a proper location on your computer. If you need to export the graph it can easily be transferred by right-clicking on it and selecting one of three options. You can send the graph to a Power Point presentation that is open, send it to an open work document or just copy it and paste it where you need it to be.
References
Boyer, K. & Verma, R. (2010). Operations & Supply Chain Management for the 21st Century. Mason, OH: South-Western.
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This article is accurate and true to the best of the author’s knowledge. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.
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© 2018 Joshua Crowder
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