All you wanted to know about laboratory tests, but were afraid to ask By Dietmar Stöckl STT Consulting - 4 - The informed patient meeting the laboratory.

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Presentation transcript:

All you wanted to know about laboratory tests, but were afraid to ask By Dietmar Stöckl STT Consulting The informed patient meeting the laboratory director Metrology Accuracy and more 1

All you wanted to know about laboratory tests Metrology United again? Yeah, seems we need all the strength we have! Sorry! Today, all is precisely true if I'm not in error...

All you wanted to know about laboratory tests Accuracy and more Ah, today's really fun!

All you wanted to know about laboratory tests The new VIM Accuracy: Closeness of agreement between a measured quantity value and a true quantity value of the measurand. Trueness: Closeness of agreement between the average of an infinite number of replicate measured quantity values and a reference quantity value. Precision: Closeness of agreement between indications or measured quantity values obtained by replicate measurements on the same or similar objects under specified conditions. Measurement error (error): Measured quantity value minus a reference quantity value. Often called total error. Systematic error: Component of measurement error that in replicate measurements remains constant or varies in a predictable manner. Random error: Component of measurement error that in replicate measurements varies in an unpredictable manner.

All you wanted to know about laboratory tests The new VIM Uses the words systematic and random error to describe the "Quality" thereof Uses the words accuracy, trueness, and precision to describe an experimental outcome Your tranquilizers, Here they come!

All you wanted to know about laboratory tests A picture says more... 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 its variance.

All you wanted to know about laboratory tests The next visit Jim where are you? What would Westgard say?

All you wanted to know about laboratory tests Resources (VIM) Measurement error (error) Measured quantity value minus a reference quantity value. Note: often called total error. Systematic [measurement] error Component of measurement error that in replicate measurements remains constant or varies in a predictable manner. Random [measurement] error Component of measurement error that in replicate measurements varies in an unpredictable manner. 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 its variance. Bias [of measurement] Estimate of a systematic measurement error. Instrumental bias Average of replicate indications minus a reference quantity value. Accuracy Closeness of agreement between a measured quantity value and a true quantity value of the measurand. Trueness Closeness of agreement between the average of an infinite number of replicate measured quantity values and a reference quantity value. Precision Closeness of agreement between indications or measured quantity values obtained by replicate measurements on the same or similar objects under specified conditions. Uncertainty [of measurement] Non-negative parameter characterizing the dispersion of the quantity values being attributed to a measurand, based on the information used.

All you wanted to know about laboratory tests Resources (VIM) metrological traceability property of a measurement result whereby the result can be related to a reference through a documented unbroken chain of calibrations, each contributing to the measurement uncertainty NOTE 1 For this definition, a ‘reference’ can be a definition of a measurement unit through its practical realization, or a measurement procedure including the measurement unit for a non-ordinal quantity, or a measurement standard. NOTE 2 Metrological traceability requires an established calibration hierarchy. measurement standard (etalon) realization of the definition of a given quantity, with stated quantity value and associated measurement uncertainty, used as a reference. commutability of a reference material property of a reference material, demonstrated by the closeness of agreement between the relation among the measurement results for a stated quantity in this material, obtained according to two given measurement procedures, and the relation obtained among the measurement results for other specified materials NOTE 1 The reference material in question is usually a calibrator and the other specified materials are usually routine samples. NOTE 2 The measurement procedures referred to in the definition are the one preceding and the one following the reference material (calibrator) in question in a calibration hierarchy (see ISO 17511).