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| Gràfic de control de variables de Shewhart (X-barra / R)× | Gràfic de control EWMA× | |
|---|---|---|
| Camp | Estadística | Estadística |
| Família | Process / pipeline | Process / pipeline |
| Any d'origen≠ | 1931 | 1959 |
| Autor original≠ | Walter A. Shewhart | S. W. Roberts |
| Tipus≠ | Statistical process control chart for variables | Statistical process control chart for small shifts |
| Font seminal≠ | Shewhart, W. A. (1931). Economic Control of Quality of Manufactured Product. D. Van Nostrand Company. ISBN: 978-0-87389-076-2 | Roberts, S. W. (1959). Control chart tests based on geometric moving averages. Technometrics, 1(3), 239–250. DOI ↗ |
| Àlies≠ | X-bar and R chart, Shewhart chart, variables control chart, process control chart | exponentially weighted moving average chart, EWMA control chart, geometric moving average chart, EWMA kontrol kartı |
| Relacionats≠ | 4 | 3 |
| 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. | The exponentially weighted moving average (EWMA) control chart, introduced by S. W. Roberts in 1959, monitors a process using a weighted average that gives the most recent observation the greatest weight while letting older observations fade geometrically. Like CUSUM, this memory makes it highly effective at detecting small, sustained shifts in the process mean, with a single smoothing parameter λ controlling how much past information the chart retains. |
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