| 1. |
- Kallner, Anders, et al.
(författare)
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An experimental study of methods for the analysis of variance components in the inference of laboratory information
- 2020
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Ingår i: Scandinavian Journal of Clinical and Laboratory Investigation. - : TAYLOR & FRANCIS LTD. - 0036-5513 .- 1502-7686. ; 80:1, s. 73-80
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Tidskriftsartikel (refereegranskat)abstract
- Measurement uncertainty (MU) can be estimated and calculated by different procedures, representing different aspects and intended use. It is appropriate to distinguish between uncertainty determined under repeatability and reproducibility conditions, and to distinguish causes of variation using analysis of variance components. The intra-laboratory MU is frequently determined by repeated measurements of control material(s) of one or several concentrations during a prolonged period of time. We demonstrate, based on experimental results, how such results can be used to identify the repeatability, pure reproducibility and intra-laboratory variance as the sum of the two. Native patient material was used to establish repeatability using the Dahlberg formula for random differences between measurements and an expanded Dahlberg formula if a non-random difference, e.g. bias, was expected. Repeatability and reproducibility have different clinical relevance in intensive care compared to monitoring treatment of chronic diseases, comparison with reference intervals or screening.
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| 2. |
- Kallner, Anders, et al.
(författare)
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Measurement repeatability profiles of eight frequently requested measurands in clinical chemistry determined by duplicate measurements of patient samples
- 2020
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Ingår i: Scandinavian Journal of Clinical and Laboratory Investigation. - : TAYLOR & FRANCIS LTD. - 0036-5513 .- 1502-7686. ; 80:3, s. 202-209
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Tidskriftsartikel (refereegranskat)abstract
- Measurement uncertainties in clinical chemistry are commonly regarded as heteroscedastic - having a constant relative standard deviation irrespective of the concentration of the measurand. The uncertainty is usually determined at two concentrations using stabilized control materials and assumed to represent the analytical goal. The purpose of the present study was to use duplicates of unselected patient samples to calculate the absolute and relative repeatability component of the intra-laboratory measurement uncertainty from duplicates, using the Dahlberg formula and analysis of variance components. Estimates were made at five different concentration intervals of ALT, AST, Calcium, Cholesterol, Creatinine, CRP, Triglycerides and TSH covering the entire concentration interval of the patient cohort. This partioning allows detailing their repeatability profiles. The calculations of the profiles were based on randomly selected results from sets of duplicates ranging from 12,000 to 65,000 pairs. The repeatability of the measurands showed substantial variability within the measuring interval. Therefore, characterizing imprecision profiles as purely homo- or heteroscedastic or by a single number may not be optimal for the intended use. The present data make a case for nuancing the evaluation of analytical goals and minimal differences of measurement results by establishing uncertainty profiles under repeatability conditions, using natural patient samples.
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| 3. |
- Kallner, Anders, et al.
(författare)
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Repeatability imprecision from analysis of duplicates of patient samples and control materials
- 2020
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Ingår i: Scandinavian Journal of Clinical and Laboratory Investigation. - : TAYLOR & FRANCIS LTD. - 0036-5513 .- 1502-7686. ; 80:3, s. 210-214
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Tidskriftsartikel (refereegranskat)abstract
- Measurement imprecision is usually calculated from measurement results of the same stabilized control material(s) obtained over time, and is therefore, principally, only valid at the concentration(s) of the selected control material(s). The resulting uncertainty has been obtained under reproducibility conditions and corresponds to the conventional analytical goals. Furthermore, the commutability of the control materials used determines whether the imprecision calculated from the control materials reflects the imprecision of measuring patient samples. Imprecision estimated by measurements of patient samples uses fully commutable samples, freely available in the laboratories. It is commonly performed by calculating the results of routine patient samples measured twice each. Since the duplicates are usually analysed throughout the entire concentration interval of the patient samples processed in the laboratory, the result will be a weighted average of the repeatability imprecision measured in the chosen measurement intervals or throughout the entire interval of concentrations encountered in patient care. In contrast, the uncertainty derived from many measurements of control materials over periods of weeks is usually made under reproducibility conditions. Consequently, the repeatability and reproducibility imprecision play different roles in the inference of results in clinical medicine. The purpose of the present review is to detail the properties of the imprecision calculated by duplicates of natural samples, to explain how it differs from imprecision calculated from single concentrations of control materials, and to elucidate what precautions need to be taken in case of bias, e.g. due to carry-over effects.
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| 4. |
- Kallner, Anders, et al.
(författare)
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Response to Dr. Sadlers comments
- 2020
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Ingår i: Scandinavian Journal of Clinical and Laboratory Investigation. - : Taylor & Francis. - 0036-5513 .- 1502-7686. ; 80:6, s. 448-449
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
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