\n| \n Possibility of determining u\u00a0<\/em>(bias<\/em>) <\/strong><\/p>\n<\/td>\n| \n Pros<\/strong><\/p>\n<\/td>\n| \n Cons<\/strong><\/p>\n<\/td>\n<\/tr>\n\n| Analysing the sample with a reference analysis procedure<\/td>\n | Bias can be determined very reliably, because the determined bias corresponds to the bias with exactly the same sample matrix as is in the real sample.<\/td>\n | It is usually very difficult to find a suitable reference procedure. Therefore this possibility is not often used at routine labs.<\/td>\n<\/tr>\n | \n| Certified reference material (CRM)\u00a0[1] <\/a><\/td>\n | Bias can be determined quite reliably, because the reference values of CRM-s are generally quite reliable.<\/td>\n | Availability of certified reference materials is limited and their matrixes are often better homogenised than in the case of real samples, leading to somewhat optimistic bias estimates.<\/td>\n<\/tr>\n | \n| Using samples of interlaboratory comparisons as reference samples<\/td>\n | Is often usable at routine labs, because labs usually participate in interlaboratory comparisons with the procedures that they use in their everyday work.<\/td>\n | The reference values are mostly derived from participant results and have therefore low reliability (high uncertainty). This leads to overestimated u\u00a0<\/em>(bias<\/em>).<\/td>\n<\/tr>\n\n| Using spiking studies<\/td>\n | Can be done at the laboratory and can be done with the real samples, thereby exactly matching the matrix.<\/td>\n | The main problem in bias determination by spiking is dispersing the analyte in the sample in the same way as the native analyte in the sample.\u00a0In the case of inhomogenous matrixes this can be very difficult.<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n In the case of all four possibilities it is critical to include also sample preparation in bias determination.<\/p>\n In the case of all four possibilities it is necessary to make an as large as possible number of replicate measurements in order to separate the bias from random effects as efficiently as possible. Bias generally changes from matrix to matrix and usually is different at different concentration levels. So, it is important to use several CRMs, several interlaboratory comparisons, etc.<\/p>\n The lower is the reliability of the reference value the higher is the u\u00a0<\/em>(bias<\/em>) estimate.<\/p>\n\n The u\u00a0<\/em>(bias<\/em>) component is found according to the following equation:<\/p>\n\n\n\n![\"10-2.png\"](\"https:\/\/sisu.ut.ee\/wp-content\/uploads\/sites\/18\/10-2.png\" "\\"10-2.png\\"") <\/td>\n | \u00a0(10.2)<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n \nRMS<\/em>bias<\/sub> is the average (root mean square) bias and is found as follows:<\/span><\/p>\n\n\n\n![\"10-3.png\"](\"https:\/\/sisu.ut.ee\/wp-content\/uploads\/sites\/18\/10-3.png\" "\\"10-3.png\\"") <\/td>\n | \u00a0(10.3)<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n \n<\/p> Where <\/span>n<\/em> is the number of bias determinations carried out and each <\/span>biasi<\/sub><\/em> is a result of an individual bias determination and is found as follows:<\/span><\/p>\n\n\n\n![\"10-4.png\"](\"https:\/\/sisu.ut.ee\/wp-content\/uploads\/sites\/18\/10-4.png\" "\\"10-4.png\\"") <\/td>\n | \u00a0(10.4)<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n Where Clabi<\/sub><\/em> is a mean of the results of analyte determination in the reference sample (e.g. in the CRM) obtained by the laboratory and Crefi<\/sub><\/em> is the reference value of the reference sample. It is important that Clabi<\/sub><\/em> corresponds to a number of replicates.<\/p>\nu\u00a0<\/em>(Cref<\/em>) is the average standard uncertainty of the reference values of the reference samples and is found as follows:<\/p>\n\n\n\n![\"10-5.png\"](\"https:\/\/sisu.ut.ee\/wp-content\/uploads\/sites\/18\/10-5.png\" "\\"10-5.png\\"") <\/td>\n | \u00a0(10.5)<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n Here <\/span>u\u00a0<\/em>(<\/span>Crefi<\/sub><\/em>) is the standard uncertainty of the <\/span>i<\/em>-th reference value. In the case of CRM analysis, spiking or analysis with a reference procedure the <\/span>u\u00a0<\/em>(<\/span>Crefi<\/sub><\/em>) can usually be reasonably found. However, in the case of interlaboratory comparisons where the consensus value of the participants is used as the reference value a reliable uncertainty of the reference value cannot be found. The best estimate in that case would be the standard deviation of the average value after elimination of outliers:<\/span><\/p>\n\n\n\n![\"10-6.png\"](\"https:\/\/sisu.ut.ee\/wp-content\/uploads\/sites\/18\/10-6.png\" "\\"10-6.png\\"") <\/td>\n | (10.6)<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n \n<\/p> Here si<\/sub><\/em> is the standard deviation of the participants in the i<\/em>-th intercomparison after elimination of outlayers and ni<\/sub><\/em> is the number of participants (again after eliminating the outliers) in the i<\/em>-th intercomparison.<\/p>\nIn the special case if a number of bias determinations were carried out using one single CRM the equation 10.2 changes into the following form:<\/p>\n \n\n\n![\"10-7.png\"](\"https:\/\/sisu.ut.ee\/wp-content\/uploads\/sites\/18\/10-7.png\" "\\"10-7.png\\"") <\/td>\n | \u00a0(10.7)<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n Where <\/span>s<\/em>bias<\/sub> is the standard deviation of the bias estimates obtained and <\/span>n<\/em> is the number of bias estimates obtained.<\/span><\/p>\nDepending on situation the <\/span>u<\/em>(<\/span>bias<\/em>) can be used as absolute or as relative value.<\/span><\/p>\nFinally, it is important to stress that the bias uncertainty component should be estimated separately for different matrixes and different concentration levels.<\/p>\n<\/div>\n ![\"selftest.png\"](\"https:\/\/sisu.ut.ee\/wp-content\/uploads\/sites\/18\/selftest.png\" "\\"selftest.png\\"") <\/a><\/p>\n\n<\/p> ***<\/p>\n [1] In simplified terms certified reference material is a material, in which the content of the analyte (or analytes) is reliably known (the material has a certificate). If the certified reference material\u2019s matrix is similar to real samples (i.e. it is not a pure compound or a solution but is e.g. milk powder, soil or blood plasma) then we call it certified matrix reference material.<\/p>\n","protected":false},"excerpt":{"rendered":" To view third-party content, please accept cookies. Change consent Estimating the uncertainty component due to possible bias http:\/\/www.uttv.ee\/naita?id=17910 https:\/\/www.youtube.com\/watch?v=hLGZsW_o81o The component u\u00a0(bias) takes into account possible bias of the measurement procedure. Reliably determining the bias of the procedure is not …<\/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-28","page","type-page","status-publish","hentry"],"acf":[],"_links":{"self":[{"href":"https:\/\/sisu.ut.ee\/measurement\/wp-json\/wp\/v2\/pages\/28","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=28"}],"version-history":[{"count":3,"href":"https:\/\/sisu.ut.ee\/measurement\/wp-json\/wp\/v2\/pages\/28\/revisions"}],"predecessor-version":[{"id":823,"href":"https:\/\/sisu.ut.ee\/measurement\/wp-json\/wp\/v2\/pages\/28\/revisions\/823"}],"wp:attachment":[{"href":"https:\/\/sisu.ut.ee\/measurement\/wp-json\/wp\/v2\/media?parent=28"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}
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