Enter your data for Normal Capability Analysis

Stat > Quality Tools > Capability Analysis > Normal

Select the option that best describes your data.

Single column

If your data are in a single column of the worksheet, complete the following steps.

1. Under Data are arranged as, select Single column.
2. In Single column, enter the column of numeric data that you want to analyze.
3. In Subgroup size, enter a column that identifies the subgroup for each measurement or enter a number that indicates the subgroup size. Enter a number for subgroups of the same size. For example, if each subgroup contains measurements for five items, enter 5. If you collected data over time without subgroups, use a subgroup size of 1. If you enter a column of subgroup IDs, the subgroup sizes do not need to be equal.
Note

Observations within each subgroup should be in adjacent rows of the worksheet. For more information on using columns to define subgroups, go to Using subgroups to assess process capability.

In this worksheet, the Diameter column contains the diameters of the piston rings. The Subgroup ID column identifies the subgroup for each measurement.
C1 C2
Diameter Subgroup ID
74.030 1
74.002 1
74.019 1
73.992 1
73.995 2
73.992 2

Subgroups across rows of

If you have subgroups arranged in rows across several columns of the worksheet, and each row represents a single subgroup, complete the following steps.

Note

If you use this option to enter your data, all subgroups must be the same size. If your subgroups are arranged in rows and the sizes differ, you can enter a missing value symbol "*" in worksheet cells as needed to make all the subgroup sizes the same.

1. Under Data are arranged as, select Subgroups across rows of.
2. In Subgroups across rows of, enter the columns of numeric data that you want to analyze.
In this worksheet, the first row of the worksheet contains the diameters of the piston rings in subgroup 1. The second row of the worksheet contains the diameters of the piston rings in subgroup 2, and so on.
C1 C2 C3
Observation 1 Observation 2 Observation 3
74.030 73.995 73.988
74.002 73.992 74.024
74.019 74.011 74.021
73.992 74.004 74.005

Specification limits

To perform the analysis, you must enter a lower specification limit, an upper specification limit, or both.

Lower spec
Enter the minimum acceptable value for the product or service. If it is not possible for measurements to fall below this value, select Boundary to define the lower specification limit as a boundary.
Upper spec
Enter the maximum acceptable value for the product or service. If it is not possible for measurements to exceed this value, select Boundary to define the upper specification limit as a boundary.
Note

When you define a specification limit as a boundary, Minitab reports the expected capability indices related to the spec limit/boundary as missing values (*). Therefore, define a limit as a boundary only if it is theoretically impossible for measurements to fall beyond the limit. For example, an upper specification limit of 100% purity is a boundary because it is not possible to exceed 100% purity. A lower specification limit of 0% purity is a boundary because it is not possible to fall below 0% purity.

Historical parameters (optional)

If you know the historical mean or the historical standard deviation of your process, or if you have an estimate obtained from past data, enter the value to use in the analysis.

Historical mean
Enter a value for the mean of the population distribution.
Historical standard deviation
Enter a value for the standard deviation of the population distribution.

If you do not enter historical parameters, Minitab estimates the mean and standard deviation from your sample data and uses those estimates to calculate process capability.

Note

If you want to specify the method that Minitab uses to estimate the standard deviation from your sample data, click Estimate.

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