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All you wanted to know about laboratory tests, but were afraid to ask. The informed patient meeting the laboratory director. Metrology Accuracy and more 2. By Dietmar Stöckl ST T Consulting - 5 -. Accuracy and more. Today What would Westgard say?. Sounds good!. Repetition.
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All you wanted to know about laboratory tests, but were afraid to ask The informed patient meeting the laboratory director Metrology Accuracy and more 2 By Dietmar Stöckl STT Consulting - 5 -
Accuracy and more Today What would Westgard say? Sounds good! All you wanted to know about laboratory tests -5-
Repetition Trueness, NOTE 2 Measurement trueness is inversely related to systematic measurement error. Bias [of measurement] Estimate of a systematic measurement error. Random error, NOTE 2 Random measurement errors of a set of replicate measurements form a distribution that can be summarized by its expectation, which is generally assumed to be zero, and itsvariance. All you wanted to know about laboratory tests -5-
What would Westgard say? JIM! How does that sound to you? Similar, but not the same! All you wanted to know about laboratory tests -5-
How do they compare? VIM Trueness, NOTE 2 … trueness is inversely related to systematic … error. Bias [of measurement] Estimate of a systematic … error. Random error, NOTE 2 Random … errors of a set of replicate measurements form a distribution that can be summarized by its … variance. All you wanted to know about laboratory tests -5-
How do they compare? Westgard Bias Random error "Distribution-based", with specified probability (95%: two-, or one-sided) z x s (z = 1.96 or 1.65) Total error "Distribution-based" Bias + z x s VIM Bias [of measurement] Random error, NOTE 2 Note 2: "Distribution-based", probability not specified s2(variance) AND "result-based" (definition) Error "Result-based" Measured value minus a reference value. All you wanted to know about laboratory tests -5-
How do they compare? Westgard Accuracy Like it or not, manufacturers and laboratories are left with the “systematic error concept of accuracy” (westgard.com/essay118.htm) VIM Accuracy Closeness of agreement between a measured quantity value and a true quantity value of the measurand. Still differences! All you wanted to know about laboratory tests -5-
Another voice • Typical total error concepts are too simplistic. • At least, sample related effects should be included. • Krouwer JS. • Setting performance goals and • evaluating total analytical error • for diagnostic assays. • Clin Chem 2002;48:919-27. All you wanted to know about laboratory tests -5-
Errors – Summary • Random error • -Analytical: SDa (CVa) • -Sample-related: SDs (CVs) • “Total”: SDt = [SDa2 + SDs2] (may be expanded) • Systematic error/Bias • Bt = Experimental mean (sufficient n) minus “reference”/”true” • Overall plus actual lot (may be expanded) • Total error • TE = Bt + z SDt • Interferences • Lipaemia, heterophilic antibodies, etc. • >Estimate frequency and magnitude of effect • >Treat separately by risk management procedures (my opinion) All you wanted to know about laboratory tests -5-
In the end I type: ... altogether, there still is hope ... In my lifetime? All you wanted to know about laboratory tests -5-
The next visit Uncertainty I love that one! All you wanted to know about laboratory tests -5-