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About this lesson
This lesson walks through an example of a variable data Gage R&R analysis. The example is demonstrated using manual data collection and equations with a spreadsheet in Microsoft Excel. The same example is then demonstrated using the statistical software program Minitab, which is often used to conduct analyses for Lean Six Sigma projects.
Download this lesson’s related exercise files.Variable Data Gage R&R Examples.xlsx
13.9 KB Variable Data Gage R&R Examples - Solution.xlsx
Variable Data Gage R&R Examples
An example of a variable data Gage R&R analysis will illustrate the power of the technique. This example is demonstrated using Means and Ranges equations with a spreadsheet in Microsoft Excel. The same example is then demonstrated using ANOVA with the statistical software program Minitab, which is often used to conduct analyses for Lean Six Sigma projects.
When to use
The example illustrates the technique. When doing your first few Gage R&R Studies, you will want to refer to the example to guide you through the process.
This examples will be based upon the data set shown below. It is for a study with three Appraisers, then items, and three trials.
The ranges for each part and appraiser have been calculated. The Mean for each part and the mean for each appraiser have also been calculated. With these the Means and Ranges calculations can be completed.
The other approach is to use the ANOVA statistical analysis methodology. This normally requires a statistical application. The most popular application for statistical analysis within the Lean Six Sigma community is Minitab. That application will be used to illustrate how to create and analyze a variable data Gage R&R Study.
Minitab provide a wizard for measurement systems analysis that is found under the Assistant pull down menu. When selecting Measurement Systems Analysis the wizard panel appears.
Variable data analysis is on the left side of the first diagonal and is labelled "measurement". The attribute data analysis is the right side labelled "appraisal". Whichever path you choose, you then have two options, either to set up the study which will create the data collection form for you, or the analysis side which will perform the calculations.
- When selecting the analysis side for variable data, a second panel is displayed. This panel will ask where information is found in your Minitab workbook.
- The Minitab workbook operates similar to an Excel spreadsheet – in fact you can directly copy and paste data form one application to the other.
- One limitation within Minitab, is that it almost always requires the information to be in columns not rows.
- If you used Minitab to set up the study, the form it created will be organized for easy analysis. You will need to tell Minitab which columns are your appraiser names, your item numbers and of course your data.
- In the process variation section, I normally will check the box for “Estimate from parts in the study.”
- If you are not familiar with Minitab, the way to select a column for one of their entry fields is to first place your cursor in the field. This will cause all available columns that are not already assigned to be shown in the window on the left.
- Highlight the column you want to use for the selected field, then drop just below the window listing all columns and click on the Select button. That column name will now be in your field.
- Do this to select a column name for every open field on the panel.
- Then when ready, click the OK button at the bottom of the panel. Minitab will soon give you results.
The Minitab results are both graphical and numerical. I find the most helpful results to be the panel shown below. In this case you can see a breakdown of repeatability and reproducibility. As mentioned before, the values are not the same as though calculated with the Means and Ranges approach, but they are similar.
Hints & tips
- If planning on doing the analysis in Minitab, do the setup with it also and use the Minitab form. The analysis then takes about 15 seconds to select the columns and see the result.
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