SPC Statistics Styles
The SPC Statistics Style determines which statistical measures displays on control charts generated during an SPC analysis. Because these charts are depicted as images, the statistics cannot be scrolled within the interface. Therefore, the statistics selected for display are optimized to fit the available space and are tailored to the specific chart type. For example, a Distribution chart displays more statistics than a Combo chart because of the larger display area.
To view and configure SPC tab styles, navigate to .
This table lists the SPC statistics and the categories:
| SPC Statistics | Category | Relevant To | Description |
|---|---|---|---|
| # Defects | Statistics | Attributes | Total number of defects identified during analysis. |
| # Ignored | Calculations | The total number of samples excluded from the data set. | |
| # Samples | Statistics | Variables | The total number of samples included in the analysis. |
| # Subgroups | Calculations | The total number of fully analysed subgroups. | |
| Actual Sigma | Statistics | Variables | The actual standard deviation of all values within the analysis range. |
| Attr Study Type | Calculations | Attributes | The type of study attribute used. |
| Calculation Mode | Calculations | Variables | The calculation mode used for calculating sigma. |
| Calculation style | Calculations | The name of the calculation style applied. | |
| CAM | Indices | Variables | CNOMO Average Aptitude Coefficient used to assess process capability. |
| CAP | Indices | Variables | The Process Aptitude Coefficient used to assess process efficiency. |
| Capability | Status | Indicates if process capability meets the defined threshold. | |
| cBar | Indices | Attributes | The mean count of defects. |
| Cp | Indices | Variables | Process capability index: (USL – LSL) ÷ 6σ (estimate). |
| Cpk | Indices | Variables | Process capability index: Minimum of (USL – Mean) ÷ 3σ and (Mean – LSL) ÷ 3σ (estimate). |
| CpkL | Indices | Variables | Lower specification referenced capability index: (Mean – LSL) ÷ 3σ (estimate). |
| CpkU | Indices | Variables | Upper specification referenced capability index: (USL – Mean) ÷ 3σ (estimate). |
| Cpm | Indices | Variables | Process capability index for one-sided tolerances. |
| CR | Indices | Variables | Capability index calculated as 1 ÷ Cp. |
| Di | Statistics | Variables | Instantaneous dispersion. |
| Estimated Sigma | Statistics | Variables | Sigma value used in Cp/Cpk calculations, based on XR, XS, or selected method. |
| Homogeneity | Status | Indicates if data passed the homogeneity test. | |
| Kurtosis | Statistics | Variables | Index indicating the peak of the distribution. |
| Last violation occured at | Status | The latest date and time of control or specification violation. | |
| LSL | Specifications | Variables | The lower specification limit. |
| Maximum Value | Statistics | Variables | The maximum sample value identified in the analysis range |
| Max-Min | Statistics | Variables | The difference between the maximum and minimum values in the analysis range. |
| Mean X | Statistics | Variables | The mean value of all individual samples. |
| Median | Statistics | Variables | The median value in the distribution of values in the analysis range. |
| Minimum Value | Statistics | Variables | The minimum sample value identified in the analysis range. |
| Moving Subgroup Size | Calculations | Variables | The number of successive samples grouped for moving analysis. |
| nBar | Indices | Attributes | Average number of items inspected associated with the SPC. |
| Nom | Specifications | Variables | The specified nominal value within the defined limits. |
| npBar | Indices | Attributes | Average number of non-conforming items associated with the SPC. |
| pBar | Indices | Attributes | Average proportion of non-conforming items inspected associated with the SPC. |
| Pp | Indices | Variables | Process performance index: (USL – LSL) ÷ 6σ (actual). |
| Ppk | Indices | Variables | Process performance index: Minimum of (USL – Mean) ÷ 3σ and (Mean – LSL) ÷ 3σ (actual). |
| PpL | Indices | Variables | Lower spec referenced capability index used in Ppk. |
| PpU | Indices | Variables | Upper spec referenced capability index used in Ppk. |
| Proportion Conforming | Indices | Attributes | Percentage of items meeting required standards. |
| RBar | Statistics | Variables | The average range value from all subgroups. |
| RwBar | Statistics | Variables | The average range calculated from all subgroups within each piece. |
| sBar | Statistics | Variables | The average standard deviations from all subgroups. |
| Skewness | Statistics | Variables | An index reflecting distribution asymmetry. |
| Specification Type | Specifications | Variables | The type of specification applied in capability assessment. |
| Stability | Status | Indicates whether any violation of control occurred during analysis. | |
| Study Type | Calculations | The type of SPC study applied. | |
| Subgroup Size | Calculations | Variables | The maximum number of samples in any subgroup. |
| Sum X | Statistics | Variables | Total of all individual sample values. |
| swBar | Statistics | Variables | Average of the standard deviations calculated within each subgroup for individual pieces. |
| Total Failures | Statistics | Attributes | The total number of defect failures. |
| uBar | Indices | Attributes | The average percentage of detected non-conformities. |
| USL | Specifications | Variables | The upper specification limit. |
| Xbb | Statistics | Variables | Average value or averages of subgroups. |
| Xbb+3 | Statistics | Variables | Average or subgroup average plus 3 estimated standard deviations. |
| Xbb+4 | Statistics | Variables | Average or subgroup averages plus 4 estimated standard deviations. |
| Xbb+5 | Statistics | Variables | Average or subgroup averages plus 5 estimated standard deviations. |
| Xbb+6 | Statistics | Variables | Average or subgroup averages plus 6 estimated standard deviations. |
| Xbb-3 | Statistics | Variables | Average or subgroup averages minus 3 estimated standard deviations. |
| Xbb-4 | Statistics | Variables | Average or subgroup averages minus 4 estimated standard deviations. |
| Xbb-5 | Statistics | Variables | Average or subgroup averages minus 5 estimated standard deviations. |
| Xbb-6 | Statistics | Variables | Average or subgroup averages minus 6 estimated standard deviations. |
| Xbb-Nom | Statistics | Variables | Difference between mean or subgroup means and nominal value. |
| Zl | Indices | Variables | Statistical index: (Mean – LSL) ÷ σ (estimate). |
| Zu | Indices | Variables | Statistical index: (USL – Mean) ÷ σ (estimate). |