Quality and Reliability Methods - SAS

Chapter 10
Variability Charts
Variability Chart and Gauge R&R Analysis
A variability chart plots the mean for each level of a second factor, with all plots side by side. Along with the
data, you can view the mean, range, and standard deviation of the data in each category, seeing how they
change across the categories. The analysis options assume that the primary interest is how the mean and
variance change across the categories.
• A traditional name for this chart is a multivar chart, but because that name is not well known, we use the
more generic term variability chart.
• A variability chart shows data side-by-side like the Oneway platform, but it has been generalized to
handle more than one grouping column.
• Variability charts are commonly used for measurement systems analysis such as gauge R&R. This
analysis analyzes how much of the variability is due to operator variation (reproducibility) and
measurement variation (repeatability). Gauge R&R is available for many combinations of crossed and
nested models, regardless of whether the model is balanced.
• Just as a control chart shows variation across time in a process, a variability chart shows the same type of
variation across categories such as parts, operators, repetitions, and instruments.
• The Variability Chart platform can compute variance components. Several models of crossed and nested
factors of purely random models are available.
• Attribute (multi-level) data can also be analyzed with this platform.
Figure 10.1 Example of a Variability Chart