{"id":24,"date":"2024-04-03T23:09:23","date_gmt":"2024-04-03T20:09:23","guid":{"rendered":"https:\/\/sisu.ut.ee\/measurement\/101-principle-absolute-and-relative-quantities\/"},"modified":"2024-08-30T08:58:19","modified_gmt":"2024-08-30T05:58:19","slug":"101-principle-absolute-and-relative-quantities","status":"publish","type":"page","link":"https:\/\/sisu.ut.ee\/measurement\/101-principle-absolute-and-relative-quantities\/","title":{"rendered":"10.1. Principle, the main equation, absolute and relative quantities, overview of the practical implementation"},"content":{"rendered":"<div>\n<p>In the Nordtest approach the uncertainty is regarded as being due to two components:<\/p>\n<ol>\n<li>The <strong>within-lab reproducibility<\/strong> (intermediate precision) component. This uncertainty component takes into account\u00a0 all uncertainty sources that are <strong>random in the long term<\/strong> (i.e. several months, preferably one year). So, quite some uncertainty sources that are systematic within a day will become random in the long term.\u00a0<a href=\"#\" data-bs-toggle=\"modal\" data-bs-target=\"#popup-modal\" data-title=\"[1]\" data-content=\" A typical example is titration if new titrant is prepared weekly. Within a given week the titrant concentration is a systematic effect, but in the long term it becomes random, because many batches of titrant will be involved. A similarly typical example is calibration graph if it is prepared daily: every day the possible bias in calibration is a systematic effect, but in the long term it becomes random.\">[1]<\/a><\/li>\n<li><span style=\"line-height: 1.6em\">The <\/span><strong style=\"line-height: 1.6em\">bias component<\/strong><span style=\"line-height: 1.6em\">. This component takes into account the systematic effects that cause long-term bias (but not those that just cause bias within a given day). The <\/span><strong style=\"line-height: 1.6em\">long-term bias<\/strong><span style=\"line-height: 1.6em\"> can be regarded as sum of procedure bias (bias inherent in the nature of the procedure) and laboratory bias (bias caused by the way how the procedure is implemented in the laboratory).<\/span><\/li>\n<\/ol>\n<p style=\"text-align: center\" class=\"Video\"><\/p><div class=\"ratio ratio-16x9 mb-3\"><div class=\"video-placeholder-wrapper video-placeholder-wrapper--16x9\">\n\t\t\t    <div class=\"video-placeholder d-flex justify-content-center align-items-center\">\n\t\t\t        <div class=\"overlay text-white p-2 w-100 text-center d-block justify-content-center align-items-center\">\n\t\t\t            <div>To view third-party content, please accept cookies.<\/div>\n\t\t\t            <button class=\"btn btn-secondary btn-sm mt-1 consent-change\">Change consent<\/button>\n\t\t\t        <\/div>\n\t\t\t    <\/div>\n\t\t\t<\/div>\n<\/div>\n<h4 style=\"text-align: center\" class=\"Video\"><strong>Introduction to uncertainty estmation based on validation and quality control data (the Nordtest approach)<\/strong> <br><a href=\"http:\/\/www.uttv.ee\/naita?id=17909\" target=\"_blank\" rel=\"noopener\">http:\/\/www.uttv.ee\/naita?id=17909<\/a><\/h4>\n<p style=\"text-align: center\"><a href=\"https:\/\/www.youtube.com\/watch?v=9oOX4CUsWjI\" target=\"_blank\" rel=\"noopener\">https:\/\/www.youtube.com\/watch?v=9oOX4CUsWjI<\/a><\/p>\n<p>The main equation of the Nordtest approach is here:<\/p>\n<table class=\"table table-hover\" border=\"0\" align=\"center\">\n<tbody>\n<tr>\n<td><img loading=\"lazy\" decoding=\"async\" width=\"179\" height=\"34\" class=\"alignnone wp-image-315\" style=\"margin-left: auto;margin-right: auto\" src=\"https:\/\/sisu.ut.ee\/wp-content\/uploads\/sites\/18\/10-1.png\" title=\"10-1.png\" alt=\"10-1.png\"><\/td>\n<td>(10.1)<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p>Here <em>u\u00a0<\/em>(<em>R<\/em><sub>w<\/sub>) stands for the within-lab reproducibility component of uncertainty and <em>u\u00a0<\/em>(<em>bias<\/em>) stands for the uncertainty component taking into account possible bias. The resulting measurement uncertainty <em>u<\/em><sub>c<\/sub> is not directly related to any specific result, because it is calculated using data from the past measurements. Therefore it can be said that the uncertainty obtained with the Nordtest approach characterizes the analysis procedure rather than a concrete result. If the uncertainty of a concrete result is needed then it is <em>assigned<\/em> to the result.<\/p>\n<p><span style=\"line-height: 1.6em\">Because of this it is necessary to decide whether to express the uncertainty in absolute terms (i.e. in the units of the measured quantity) or in the relative terms (i.e. as a ratio of uncertainty to the value of the measured quantity or a percentage of the value of the measured quantity). The rules of thumb:<\/span><\/p>\n<ul>\n<li><strong>At low concentrations (near detection limit, trace level) use absolute uncertainties<br><\/strong>Uncertainty is not much dependent on analyte level<\/li>\n<\/ul>\n<ul>\n<li><strong>At medium and higher concentrations use relative uncertainties<br><\/strong>Uncertainty is roughly proportional to analyte level<\/li>\n<\/ul>\n<ul>\n<li><strong>In general: use whichever is more constant with changing concentration.<\/strong><\/li>\n<\/ul>\n<\/div>\n<p style=\"text-align: center\"><span style=\"line-height: 1.6em\">\u00a0<div class=\"ratio ratio-16x9 mb-3\"><div class=\"video-placeholder-wrapper video-placeholder-wrapper--16x9\">\n\t\t\t    <div class=\"video-placeholder d-flex justify-content-center align-items-center\">\n\t\t\t        <div class=\"overlay text-white p-2 w-100 text-center d-block justify-content-center align-items-center\">\n\t\t\t            <div>To view third-party content, please accept cookies.<\/div>\n\t\t\t            <button class=\"btn btn-secondary btn-sm mt-1 consent-change\">Change consent<\/button>\n\t\t\t        <\/div>\n\t\t\t    <\/div>\n\t\t\t<\/div>\n<\/div><\/span><\/p>\n<h4 style=\"text-align: center\"><strong style=\"line-height: 1.6em\">The main equation of the Nordtest approach. Absolute and relative quantities<br><\/strong><a style=\"line-height: 1.6em\" href=\"http:\/\/www.uttv.ee\/naita?id=17911\" target=\"_blank\" rel=\"noopener\">http:\/\/www.uttv.ee\/naita?id=17911<\/a><\/h4>\n<p style=\"text-align: center\"><a href=\"https:\/\/www.youtube.com\/watch?v=MH8CixjySjI\" target=\"_blank\" rel=\"noopener\">https:\/\/www.youtube.com\/watch?v=MH8CixjySjI<\/a><\/p>\n<p style=\"text-align: center\">\u00a0<\/p><div class=\"ratio ratio-16x9 mb-3\"><div class=\"video-placeholder-wrapper video-placeholder-wrapper--16x9\">\n\t\t\t    <div class=\"video-placeholder d-flex justify-content-center align-items-center\">\n\t\t\t        <div class=\"overlay text-white p-2 w-100 text-center d-block justify-content-center align-items-center\">\n\t\t\t            <div>To view third-party content, please accept cookies.<\/div>\n\t\t\t            <button class=\"btn btn-secondary btn-sm mt-1 consent-change\">Change consent<\/button>\n\t\t\t        <\/div>\n\t\t\t    <\/div>\n\t\t\t<\/div>\n<\/div>\n<h4 style=\"text-align: center\"><strong style=\"line-height: 1.6em\">Overview of the practical implementation of the Nordtest approach<br><\/strong><a style=\"line-height: 1.6em\" href=\"http:\/\/www.uttv.ee\/naita?id=17912\" target=\"_blank\" rel=\"noopener\">http:\/\/www.uttv.ee\/naita?id=17912<\/a><\/h4>\n<p style=\"text-align: center\"><a href=\"https:\/\/www.youtube.com\/watch?v=hPrncfXr7Ok\" target=\"_blank\" rel=\"noopener\">https:\/\/www.youtube.com\/watch?v=hPrncfXr7Ok<\/a><\/p>\n<p>The main steps of the process of measurement uncertainty evaluation with the Nordtest approach:<\/p>\n<ol>\n<li><span style=\"line-height: 1.6em\">Specify measurand<\/span><\/li>\n<li><span style=\"line-height: 1.6em\">Quantify <\/span><em style=\"line-height: 1.6em\">R<\/em><sub>w <\/sub><span style=\"line-height: 1.6em\">component <\/span><strong style=\"line-height: 1.6em\"><em>u<\/em><\/strong><strong style=\"line-height: 1.6em\">(<\/strong><strong style=\"line-height: 1.6em\"><em>R<\/em><\/strong><strong style=\"line-height: 1.6em\"><sub>w<\/sub>)<\/strong><\/li>\n<li><span style=\"line-height: 1.6em\">Quantify bias component <\/span><strong style=\"line-height: 1.6em\"><em>u<\/em><\/strong><strong style=\"line-height: 1.6em\">(<em>bias<\/em>)<\/strong><\/li>\n<li><span style=\"line-height: 1.6em\">Convert components to standard uncertainties <\/span><strong style=\"line-height: 1.6em\"><em>u<\/em>(<em>x<\/em>)<\/strong><\/li>\n<li><span style=\"line-height: 1.6em\">Calculate combined standard uncertainty <\/span><strong style=\"line-height: 1.6em\"><em>u<\/em><\/strong><sub>c<\/sub><\/li>\n<li><span style=\"line-height: 1.6em\">Calculate expanded uncertainty <\/span><strong style=\"line-height: 1.6em\"><em>U<\/em><\/strong><\/li>\n<\/ol>\n<p>***<\/p>\n<p>[1]\u00a0A typical example is titration if new titrant is prepared weekly. Within a given week the titrant concentration is a systematic effect, but in the long term it becomes random, because many batches of titrant will be involved. A similarly typical example is calibration graph if it is prepared daily: every day the possible bias in calibration is a systematic effect, but in the long term it becomes random.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>In the Nordtest approach the uncertainty is regarded as being due to two components: The within-lab reproducibility (intermediate precision) component. This uncertainty component takes into account\u00a0 all uncertainty sources that are random in the long term (i.e. several months, preferably &#8230;<\/p>\n","protected":false},"author":14,"featured_media":0,"parent":0,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"_acf_changed":false,"inline_featured_image":false,"footnotes":""},"class_list":["post-24","page","type-page","status-publish","hentry"],"acf":[],"_links":{"self":[{"href":"https:\/\/sisu.ut.ee\/measurement\/wp-json\/wp\/v2\/pages\/24","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/sisu.ut.ee\/measurement\/wp-json\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/sisu.ut.ee\/measurement\/wp-json\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/sisu.ut.ee\/measurement\/wp-json\/wp\/v2\/users\/14"}],"replies":[{"embeddable":true,"href":"https:\/\/sisu.ut.ee\/measurement\/wp-json\/wp\/v2\/comments?post=24"}],"version-history":[{"count":2,"href":"https:\/\/sisu.ut.ee\/measurement\/wp-json\/wp\/v2\/pages\/24\/revisions"}],"predecessor-version":[{"id":822,"href":"https:\/\/sisu.ut.ee\/measurement\/wp-json\/wp\/v2\/pages\/24\/revisions\/822"}],"wp:attachment":[{"href":"https:\/\/sisu.ut.ee\/measurement\/wp-json\/wp\/v2\/media?parent=24"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}