Specify the default sigma tolerance, capability index naming convention, process stage,
capability calculation method, display options, and confidence intervals. The defaults
remain in effect until you change them, even after you exit Minitab.
- Use tolerance of K × σ for capability statistics
- To calculate the capability statistics using an interval other than 6
standard deviations wide (3 on either side of the process mean), enter the
number here.
- Capability Index Naming Convention
- Select the convention that Minitab uses to name capability indices.
- Six Sigma: Use Six Sigma names for capability indices.
- AIAG/VDA: Use AIAG/VDA names for capability indices. The names depend on
the selected process stage and capability calculation method.
-
- Process stage
-
When you select AIAG/VDA, select the stage of the capability assessment.
- Machine performance: Use names for machine performance indices.
- Process performance: Use names for process performance indices.
- Process capability: Use names for process capability indices.
- Capability Calculation Method
- Select the method that Minitab uses to calculate capability statistics.
- Z-score method: Use the Z-score method, also called the Minitab method.
- ISO method (geometric): Use the ISO method, also called the geometric method.
- Display
-
Specify the statistics to display.
- Capability statistics: Display capability statistics.
- Benchmark Z's (σ level): Display benchmark Z statistics.
- CCpk or CCwk: Display the centered capability index. Minitab displays CCpk
for the Six Sigma convention and CCwk for the AIAG/VDA
convention.
- Parts per million: Display the values in parts per million (PPM).
- Percents: Display the values as percentages.
- Confidence Intervals
- Select Include confidence intervals to display confidence intervals for the capability indices.
- Confidence level
- Enter a confidence level
between 0 and 100. Usually, a confidence level of 95% works
well. A 95% confidence level indicates that if you took 100
random samples from the process, you could expect approximately
95 of the samples to produce confidence intervals that contain
the actual value of the capability index for the process (if all
the process data could be collected and analyzed).
- For a given set of data, a
lower confidence level produces a narrower confidence interval,
and a higher confidence level produces a wider confidence
interval. The width of the interval also tends to decrease with
larger sample sizes. Therefore, you may want to use a confidence
level other than 95%, depending on your sample size, as follows:
- If your sample size is small, a 95% confidence interval
may be too wide to be useful. Using a lower confidence
level, such as 90%, will produce a narrower interval.
However, the likelihood that the interval contains the
capability index for the process decreases.
- If your sample size is large, you may want to consider
using a higher confidence level, such as 99%. With a
large sample, a 99% confidence level may still produce a
reasonably narrow interval while increasing the
likelihood that the interval contains the capability
index for the process.
- Confidence intervals
- Select the type of confidence interval or bound that you want to
display:
- One-sided: Displays lower confidence bounds for capability
indices and upper confidence bounds for PPM or %
out-of-specification limits. Use one-sided confidence
bounds for the following:
- To be more confident that a capability index is
greater than a required value. For example, to be
more confident that Cp is greater than 1.33.
- To be more confident that a PPM or %
out-of-specification limits is less than a
required value. For example, to be more confident
that PPM Total out-of-specification is less than
100.
- Two-sided: Display a confidence interval that has both a lower
and an upper confidence bound.
