{"id":4626,"date":"2026-08-12T15:44:37","date_gmt":"2026-08-12T13:44:37","guid":{"rendered":"https:\/\/ellistat.com\/?post_type=guide-dutilisateur&#038;p=4626"},"modified":"2026-08-12T15:44:37","modified_gmt":"2026-08-12T13:44:37","slug":"detail","status":"publish","type":"guide-dutilisateur","link":"https:\/\/ellistat.com\/en\/guide-dutilisateur\/detail\/","title":{"rendered":"Detail"},"content":{"rendered":"<h2 class=\"wp-block-heading\">1. The Specifications Table<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">At the top of the screen, a table summarizes the definitions of each characteristic. The main columns are:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>name\u00a0<\/strong>: the variable's name; ;<\/li>\n\n\n\n<li><strong>sigma<\/strong>\u00a0and\u00a0<strong>short term<\/strong>\u00a0: the two distributions; ;<\/li>\n\n\n\n<li><strong>distribution<\/strong>\u00a0and\u00a0<strong>legal compliance<\/strong>\u00a0: the adjusted law and the quality of that adjustment; ;<\/li>\n\n\n\n<li><strong>min\/max tolerance<\/strong>,\u00a0<strong>LCI<\/strong>\u00a0and\u00a0<strong>LCS<\/strong>\u00a0: specification and control limits; ;<\/li>\n\n\n\n<li><strong>target<\/strong>\u00a0and\u00a0<strong>nominal<\/strong>\u00a0: the target value.<\/li>\n<\/ul>\n\n\n\n<blockquote class=\"wp-block-quote is-layout-flow wp-block-quote-is-layout-flow\">\n<p class=\"wp-block-paragraph\">\ud83d\udca1 The column&nbsp;<strong>Compliance with the law<\/strong>&nbsp;is the first thing to check. All capability indices assume a specific distribution; if the fit is poor, the displayed Cp and Cpk values are meaningless, and you must change the distribution or transform the data.<\/p>\n<\/blockquote>\n\n\n\n<figure class=\"wp-block-image size-full\"><img loading=\"lazy\" decoding=\"async\" width=\"644\" height=\"420\" src=\"https:\/\/ellistat.com\/wp-content\/uploads\/detail.png\" alt=\"\" class=\"wp-image-4627\" srcset=\"https:\/\/ellistat.com\/wp-content\/uploads\/detail.png 644w, https:\/\/ellistat.com\/wp-content\/uploads\/detail-300x196.png 300w, https:\/\/ellistat.com\/wp-content\/uploads\/detail-18x12.png 18w\" sizes=\"auto, (max-width: 644px) 100vw, 644px\" \/><\/figure>\n\n\n\n<h2 class=\"wp-block-heading\">2. The Charts<\/h2>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>Histogram<\/strong>\u00a0: the shape of the distribution, showing the fitted distribution superimposed on it and the tolerance limits. At a glance, one can see skewness, excessive dispersion, and bimodality\u2014a common sign of a mixture of two populations, two machines, or two batches of material.<\/li>\n\n\n\n<li><strong>Henry's Right<\/strong>\u00a0: The data points align if the distribution follows the law. This is a more sensitive visual test than the histogram, especially at the tails of the distribution\u2014precisely where nonconformities occur.<\/li>\n\n\n\n<li><strong>Control Chart<\/strong>\u00a0: chronology. It answers a question that the histogram does not address: Is the process\u00a0<strong>stable<\/strong>\u00a0?<\/li>\n\n\n\n<li><strong>Scope<\/strong>\u00a0: the variation within each sample over time.<\/li>\n\n\n\n<li><strong>EWMA<\/strong>\u00a0: a weighted moving average, which is more responsive to small, sustained deviations than a traditional map.<\/li>\n<\/ul>\n\n\n\n<blockquote class=\"wp-block-quote is-layout-flow wp-block-quote-is-layout-flow\">\n<p class=\"wp-block-paragraph\">\u26a0\ufe0f Histograms and control charts are not interchangeable. A process that is drifting slowly may produce a histogram that looks quite acceptable: the measurements from the beginning and the end blend together, and the overall distribution appears wide but centered. Only the control chart reveals the drift.<\/p>\n<\/blockquote>\n\n\n\n<h2 class=\"wp-block-heading\">3. Centered on the average or centered on the target<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">The charts can be interpreted using either of two reference frames:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>\u00a0<strong>Center-mid<\/strong>\u00a0: The confidence intervals are constructed around the observed mean. We assess the\u00a0<strong>stability<\/strong>\u00a0: Does the process remain true to itself?<\/li>\n\n\n\n<li><strong>Center-aligned<\/strong>\u00a0: The limits are set around the target value. We evaluate the\u00a0<strong>compliance<\/strong>\u00a0: Does the process produce what is required?<\/li>\n<\/ul>\n\n\n\n<blockquote class=\"wp-block-quote is-layout-flow wp-block-quote-is-layout-flow\">\n<p class=\"wp-block-paragraph\">\ud83d\udca1 A process can be perfectly stable yet consistently off-target. When centered on the average, it appears to be under control; when centered on the target, the deviation becomes apparent. Look at both.<\/p>\n<\/blockquote>\n\n\n\n<h2 class=\"wp-block-heading\">4. Detection Rules<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">Beyond simply exceeding the limit, <a href=\"https:\/\/ellistat.com\/en\/data-analysis-solutions\/\" data-type=\"page\" data-id=\"905\">Ellistat Data Analysis<\/a> indicates unlikely configurations under the assumption of a stable process:<\/p>\n\n\n\n<figure class=\"wp-block-table\"><table class=\"has-fixed-layout\"><thead><tr><td><strong>Rule<\/strong><\/td><td><strong>What it detects<\/strong><\/td><\/tr><\/thead><tbody><tr><td><strong>Trend<\/strong><\/td><td>A series of points that rise or fall: tool wear, thermal drift.<\/td><\/tr><tr><td><strong>Same side<\/strong><\/td><td>A series of points on the same side of the mean: the process has moved to a new level.<\/td><\/tr><tr><td><strong>Close to the Limits<\/strong><\/td><td>Clusters of points near the boundaries: underestimated dispersion or population mixing.<\/td><\/tr><tr><td><strong>Reciprocating motion<\/strong><\/td><td>A systematic alternation: often two sources alternating, two setups, two operators.<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<p class=\"wp-block-paragraph\">The Landmark&nbsp;<strong>Alert<\/strong>&nbsp;highlights the relevant points.<\/p>\n\n\n\n<blockquote class=\"wp-block-quote is-layout-flow wp-block-quote-is-layout-flow\">\n<p class=\"wp-block-paragraph\">\ud83d\udca1 These rules increase sensitivity to minor deviations, but each one adds the risk of a false alarm. In a process that\u2019s already under control, activating too many of them will set off the alarm for no reason.<\/p>\n<\/blockquote>\n\n\n\n<h2 class=\"wp-block-heading\">5. Capabilities<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">Four indicators, two distinctions to be aware of:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>Cp and Cpk<\/strong>\u00a0use dispersion\u00a0<strong>short term<\/strong>\u00a0: the performance the process is capable of if it remains stable.<\/li>\n\n\n\n<li><strong>Pp and Ppk<\/strong>\u00a0use dispersion\u00a0<strong>overall<\/strong>\u00a0: the actual performance delivered, including deviations.<\/li>\n\n\n\n<li><strong>Cp and Pp<\/strong>\u00a0ignore centering; ;\u00a0<strong>Cpk and Ppk<\/strong>\u00a0take this into account.<\/li>\n<\/ul>\n\n\n\n<p class=\"wp-block-paragraph\">When viewed together, the four are more meaningful than each one on its own:<\/p>\n\n\n\n<figure class=\"wp-block-table\"><table class=\"has-fixed-layout\"><thead><tr><td><strong>Finding<\/strong><\/td><td><strong>Interpretation<\/strong><\/td><\/tr><\/thead><tbody><tr><td>High Cp, low Cpk<\/td><td>A fairly accurate method, but&nbsp;<strong>off-center<\/strong>. Can be corrected by adjustment.<\/td><\/tr><tr><td>Cp \u2248 Cpk, both of which are low<\/td><td>Method&nbsp;<strong>too scattered<\/strong>. Requires a fundamental technical fix.<\/td><\/tr><tr><td>High Cp, low Pp<\/td><td>A method that is capable but&nbsp;<strong>unstable<\/strong>&nbsp;: It's drifting. Look for the cause over time.<\/td><\/tr><tr><td>Cp \u2248 Pp<\/td><td>Stable trend; the short term reflects the long term.<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<blockquote class=\"wp-block-quote is-layout-flow wp-block-quote-is-layout-flow\">\n<p class=\"wp-block-paragraph\">\ud83d\udca1 The \u00abHigh Cp, Low Pp\u00bb scenario is the most common and the most frequently misinterpreted: technically, there\u2019s nothing wrong\u2014it\u2019s the process control that\u2019s slipping. A well-maintained control chart can resolve this without any investment.<\/p>\n<\/blockquote>\n\n\n\n<h2 class=\"wp-block-heading\">6. Distribution Analysis<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">A very comprehensive distribution analysis is provided, including goodness-of-fit tests, skewness, kurtosis, and entropy parameters, as well as outlier detection. You can select the distribution; the \"Goodness-of-Fit\" button provides a summary of the goodness-of-fit tests.<\/p>\n\n\n\n<figure class=\"wp-block-image size-full\"><img loading=\"lazy\" decoding=\"async\" width=\"964\" height=\"340\" src=\"https:\/\/ellistat.com\/wp-content\/uploads\/statdescr.png\" alt=\"\" class=\"wp-image-4628\" srcset=\"https:\/\/ellistat.com\/wp-content\/uploads\/statdescr.png 964w, https:\/\/ellistat.com\/wp-content\/uploads\/statdescr-300x106.png 300w, https:\/\/ellistat.com\/wp-content\/uploads\/statdescr-768x271.png 768w, https:\/\/ellistat.com\/wp-content\/uploads\/statdescr-18x6.png 18w\" sizes=\"auto, (max-width: 964px) 100vw, 964px\" \/><\/figure>","protected":false},"featured_media":0,"menu_order":30,"template":"","meta":{"_acf_changed":true},"menu-guide-dutilisateur":[22],"class_list":["post-4626","guide-dutilisateur","type-guide-dutilisateur","status-publish","hentry","menu-guide-dutilisateur-4-statistiques-descriptives"],"acf":[],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v28.4 - 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