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Title: Το διάγραμμα EWMA στον εσωτερικό έλεγχο ποιότητας των αναλυτών κλινικής χημείας
Authors: Καρκαλούσος, Πέτρος
Item type: Journal article
Keywords: Εκθετικός βαρυκεντρικός κινούμενος μέσος;Συστημικό σφάλμα;Συντελεστής βαρύτητας;Εσωτερικός έλεγχος ποιότητας;Αναλυτές;EWMA;Systematic errors;Weighting factor;Internal quality control;Analyzers;Clinical chemistry
Subjects: Medicine
Issue Date: 5-May-2015
Date of availability: 5-May-2015
Language: Greek
Citation: Καρκαλούσος, Π. (2005) To διάγραμμα EWMA στον εσωτερικό έλεγχο ποιότητας των αναλυτών κλινικής χημείας. "Εφαρμοσμένη Κλινική Μικροβιολογία και Εργαστηριακή Διαγνωστική", 10 (3), σ. 136-146. Διαθέσιμο στο: [Έγινε Πρόσβαση: 05/05/2015].
Journal: Εφαρμοσμένη Κλινική Μικροβιολογία και Εργαστηριακή Διαγνωστική
Type of Journal: With a review process (peer review)
Table of contents: Τhe control chart EWMA («Exponentia ll y weighting moving average») invented in 1959. Although its large industrial application, it introduced into the field of the internal quality control of clinical chemistry just recently. EWMA differs dramatically from the widely used Levey- Jennings chart because its upper and lower control limits are exponential functions and it converts the daily control values into “smoothed ”values. The smoothed values (z) depend on the daily control value and also on the previous ones. The percentage of today and previo us control values which are contained into the valuez depends on the weighting factor λ with which the daily values are multiplied. The upper and low ercontrol limits of EWMA diagram depend on the weighting factor and the coefficient L. Coefficient L specifies the distance between the control limits and the central value-target of the chart. The correlation between λ and L have already been studied and us efultables and diagrams are at the user ’s disposal. Both coefficient depend on the size of the shift of the controls me an value which the user wants to detect. The values 0,1 as λ a nd 2,7 as L are the most appropriate EWMA coefficients for most cases. The EWMA chart is ideal for the detection of small systematic errors. Such errors are the shifts of controls mean value and the drift of daily control values towards one direction up or down. Especially it is appropriate for the detection of small shifts lower than one standard deviation. Such small shifts can not be detect from the limits of Levey-Jennings chart and many times are also unsighted from the Westgard rules. Despite its complicated calculations and the need of computer power, its daily use is very simple. EWMA can be plotted together with Levey-Jennings chart. In th is case Levey-Jennings diagram will detect random and large systematic errors and EWMA all kinds of systematic errors. Such combination will reduce the use of Westgardrules and it will make the detection of analytical errors a quite simple process.
Access scheme: Publicly accessible
License: Αναφορά Δημιουργού-Μη Εμπορική Χρήση-Όχι Παράγωγα Έργα 3.0 Ηνωμένες Πολιτείες
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