Select the analysis options for Nonparametric Capability Analysis

Target

If your process has a target value, enter the number. Minitab displays the target value on the capability histogram and the process data table.

Use tolerance of K × σ for capability statistics K =

Enter a value to specify the percentiles for the spread of the process. The value defines percentiles that correspond to a number of standard deviations from a normal distribution. For example, a value of 6 compares the width of the specification limits to percentiles that include 99.7% of the data because a width of 3σ to either side of the mean in a normal distribution includes approximately 99.7% of the data. A value of 5.15 defines percentiles that include 99% of the data.

Minitab interprets the K value as the width of a two-sided tolerance. If you want to use a one-sided tolerance, enter a two-sided tolerance value that is twice that of the one-sided tolerance. For example, to use percentiles that correspond to a one-sided tolerance of 3σ for a normal distribution, enter 6.

Note

If you want the tolerance value that you enter to be the default setting for every capability analysis that you perform, choose File > Options > Control Charts and Quality Tools > Capability Analysis and enter the default tolerance.

Display

Select how you want to display the observed out-of-specification values:

Parts per million: Display the values in parts per million (PPM).
Percents: Display the values as percentages.

Note

If you want to change which statistics display by default, choose File > Options > Control Charts and Quality Tools > Capability Analysis and change the default display setting.

Include confidence intervals

Select 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 of the same size 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 upper confidence bounds for PPM or % out-of-specification limits. Use one-sided confidence bounds 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.

Title

You can enter a new title for the process capability report.