Process capability
Set up, run, and review this analysis in Lifescio.
Supported analysis
Enter rational subgroups of measurements. Cp and Cpk use estimated within-subgroup variation; Pp and Ppk use overall variation. Cpk and Ppk also account for the mean’s distance from the nearest specification limit.
Supported scope: The indices assume a suitable normal process and representative subgrouping. Specification limits come from product requirements, not the observed data. An unstable or nonnormal process can make these indices misleading; they do not replace control charts.
Prepare data and configure the analysis
Enter one Rational subgroups row per subgroup, with the same number of measurement columns in every row. At least three rows and two measurements per subgroup are required. Use measurements in one consistent unit and set Lower specification limit below Upper specification limit.
The tool pools within-subgroup variances for the within standard deviation and uses all observations for overall standard deviation. It expects a meaningful subgroup design; simply splitting a long list into convenient equal blocks does not justify the interpretation.
Input reference (3 fields)
Enter your data and prespecified choices. Ranges include both limits. For table fields, use cell editing, Paste data, or Import CSV / TSV. Review whether the first imported row contains headings and map the source columns before applying the import. Empty numeric cells are not treated as zero. Open file is for an exported Lifescio analysis JSON file, not a spreadsheet.
| Input | Format | Allowed range | Guidance |
|---|---|---|---|
| Rational subgroups | Table | — | Columns in order: Value 1; Value 2; Value 3; Value 4. |
| Lower specification limit | Number | -1000000–1000000 | — |
| Upper specification limit | Number | -1000000–1000000 | — |
Run and review
- Give the analysis a descriptive name and review every example value. Record units, data preparation, and planning assumptions in Reproducibility & notes. For simulations, record the seed and replication or sampling settings.
- Choose Run analysis. Resolve input errors before interpreting output. In the connected app, a run uses a saved input revision; local preview runs need the page to stay open.
- Review Diagnostics for method limitations, warnings, and available numerical checks. A completed run means computation finished; it does not establish that the assumptions fit your study.
- Use the Result table selector to inspect each output. Editing inputs does not recalculate existing results: an earlier-input notice means you need to run again to obtain matching results.
Understand the outputs
Capability indices includes mean, within and overall standard deviations, Cp/Cpk, Pp/Ppk, and observed versus normal-predicted out-of-spec proportions. Proportions are decimals, so 0.02 means 2%.
The Subgroup means plot can reveal broad shifts but is not itself a control chart with stability limits. The application does not report uncertainty intervals for capability indices or automatically test normality. Interpret the point estimates with the process and sampling limitations.
Troubleshooting and common mistakes
Equal or reversed specifications are rejected. Zero within-subgroup or overall variation prevents meaningful capability calculation; check measurement resolution and whether rows were accidentally duplicated.
If Cpk is much lower than Cp, inspect centering. If within and overall indices disagree, examine subgroup shifts. Do not replace specification limits with control limits to improve a reported index. For nonnormal or unstable production, use an appropriate capability model after investigating the process.
After correcting inputs, run again and check that the results belong to the new input snapshot. Increasing simulation draws improves numerical precision only; it does not repair invalid data or an unsuitable model.
Save, compare, and export
In the connected app, Save analysis retains the inputs in your account. Run history lets you inspect earlier runs, each with the input revision it used. In local preview, Save analysis downloads an input file instead; download results before leaving the page.
Use Result + inputs for a JSON archive containing the completed result and its inputs, Download CSV for the selected result table, PDF report for a report, and a chart's SVG button for its figure. Table displays round to three decimals; CSV and JSON exports retain calculation precision. Use those values when assessing a result near a decision boundary.
To reopen an archive, select the matching analysis method and choose Open file. Imported inputs start a new draft; a result archive can also display its retained result. It does not attach itself to an existing account analysis or recompute the result. Save or run the imported draft when you want a new account record.