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| Gràfic de control de variables de Shewhart (X-barra / R)× | Gràfics de control d'atributs (p, np, c, u)× | |
|---|---|---|
| Camp | Estadística | Estadística |
| Família | Process / pipeline | Process / pipeline |
| Any d'origen | 1931 | 1931 |
| Autor original | Walter A. Shewhart | Walter A. Shewhart |
| Tipus≠ | Statistical process control chart for variables | Statistical process control charts for count/proportion data |
| Font seminal | Shewhart, W. A. (1931). Economic Control of Quality of Manufactured Product. D. Van Nostrand Company. ISBN: 978-0-87389-076-2 | Shewhart, W. A. (1931). Economic Control of Quality of Manufactured Product. D. Van Nostrand Company. ISBN: 978-0-87389-076-2 |
| Àlies | X-bar and R chart, Shewhart chart, variables control chart, process control chart | p-chart, np-chart, c-chart, u-chart |
| Relacionats | 4 | 4 |
| Resum≠ | The Shewhart control chart, invented by Walter Shewhart at Bell Labs in the 1920s and set out in his 1931 book, is the foundational tool of statistical process control. It plots a process statistic — typically the subgroup mean (X-bar) and range (R) — over time against a center line and three-sigma control limits, distinguishing the natural common-cause variation inherent in a stable process from special-cause variation that signals something has changed and warrants investigation. | Attributes control charts extend Shewhart's framework to count and proportion data — quality characteristics that are classified rather than measured. The p- and np-charts monitor the proportion or number of defective items using the binomial distribution, while the c- and u-charts monitor the number of defects per unit using the Poisson distribution. They are the standard statistical-process-control tools when inspection yields pass/fail or defect counts rather than continuous measurements. |
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