Estimation Of Measurement Uncertainty Research Articles

Uncertainty evaluation in time-dependent measurements

Data quality plays a strong role in modelling and is fundamental to ensure that obtained analyses and results are reliable. Data uncertainty is related to the measurement’s imperfections that will cause an error in the obtained numerical value. In this way, data quality could be measured through uncertainty. Although there are well-established methods for uncertainty evaluation in independent measurements, there is a gap of methods in the case of time-dependent measurements. This study aims to propose a general methodology to evaluate the uncertainty of time-dependent measurements. Fitting an appropriate model to the measurements and then resampling and refitting a model, the uncertainty estimation of each data point is possible. The approach was validated using measurements obtained from typical time series models and compared with theoretical values. Further, real data from a water system is also used to illustrate the method’ capacity for uncertainty estimation of single time measurements.

Filling in the GAPS: validation of anion gap (AGAP) measurement uncertainty estimates for use in clinical decision making.

We compare measurement uncertainty (MU) calculations to real patient result variation observed by physicians using as our model anion gap (AGAP) sequentially measured on two different instrument types. An approach for discretely quantifying the pre-analytical contributions and validating AGAP MU estimates for interpretation of patient results is proposed. AGAP was calculated from sodium, chloride, and bicarbonate reported from chemistry or blood gas analyzers which employ different methodologies and specimen types. AGAP MU was calculated using a top-down approach both assuming no correlation between measurands and alternatively, including consideration of measurand correlation. MU-derived reference change values (RCV) were calculated between chemistry and blood gas analyzers results. Observational paired AGAP data (n=39,626 subjects) was obtained from retrospectively analyzed specimens from five urban tertiary care hospitals in Calgary, Alberta, Canada. The MU derived AGAP RCV for paired specimen data by the two platforms was 5.2-6.1mmol/L assuming no correlation and 2.6-3.1mmol/L assuming correlation. From the paired chemistry and blood gas data, total observed variation on a reported AGAP has a 95% confidence interval of ±6.0mmol/L. When the MU-derived RCV assuming correlation is directly compared against the observed distribution of patient results, we obtained a pre-analytical variation contribution of 2.9-3.5mmol/L to the AGAP observed variation. In contrast, assuming no correlation leads to a negligible pre-analytical contribution (<1.0mmol/L). MU estimates assuming no correlation are more representative of the total variation seen in real patient data. We present a pragmatic approach for validating an MU calculation to inform clinical decisions and determine the pre-analytical contribution to MU in this system.

Measurement Uncertainty Estimation for the Quantitative Determination of Elemental Impurities in Active Pharmaceutical Ingredients Using Microwave Digestion Followed by ICP-OES According to USP &lt;232&gt; and &lt;233&gt; Specifications

Measurement Uncertainty Estimation for the Quantitative Determination of Elemental Impurities in Active Pharmaceutical Ingredients Using Microwave Digestion Followed by ICP-OES According to USP &lt;232&gt; and &lt;233&gt; Specifications

Measuring the uncertainty assessment of an experimental device used to determine the thermo-optico-physical properties of translucent construction materials

Studying the thermo-optical properties of construction materials (i.e. thermal conductivity, optical reflectance, optical transmittance, and optical absorbance) is essential for improving human comfort within a building. Typically, these properties are measured independently using specific equipment. The emergence of new innovative construction structures, such as translucent materials, makes the experimental characterization of these properties more challenging to observe. Recently, a new device, called MulticoefMeter (McM), which rapidly and simultaneously measures all these properties, has been created. The study described in this article covers the calculation technique for estimating measurement uncertainties linked to morphology, the parts, and the physical formula of the experimental apparatus. The measurement uncertainty estimates are obtained from knowledge of the color of the system’s walls, placement, and form of the McM components, placement of the measurement sensors, and the application of measurement collection equipment. Therefore, a thorough calculation analysis was performed on the sub-systems. Calculations are divided into two categories: those based on mathematical tools and information given by the makers and those based on experimental observations obtained during reliability testing. These uncertainties originate from statistical tools, geometric tolerance of the system, comparison with standards, and the error propagation laws of the physical models’ link with the device. All these uncertainties were summed up and given a global value, no more than 5%, conforming to the ASTM standard (E1225). Finally, a general method to quantify the measurement uncertainty value of any experimental device was proposed.

A Monte Carlo approach to evaluate the local measurement uncertainty in transient heat transfer experiments using liquid crystal thermography

This work presents an improved estimation of the local measurement uncertainty of transient heat transfer experiments using Thermochromic Liquid Crystals (TLC). Additional signal analysis steps and a Monte Carlo (MC) approach are added to the evaluation routine. As a result, the local uncertainty in the indication time of the maximum green intensity is determined. All other input quantities for the heat transfer coefficient calculation are provided with their characteristic distribution function introducing additional uncertainties. As a final result, lower and upper boundaries for a confidence interval with a user defined confidence level for the heat transfer coefficient are calculated locally for single pixels. The new method is applied to own measurement data from a transient TLC experiment. The local measurement uncertainty is compared to the traditional approach based on error propagation. Hence, the advantages of taking the non-linearity and the local uncertainty in the peak detection into consideration are shown.

Comparing measurement uncertainty values.

Estimates of measurement uncertainty (MU) are now ubiquitous in analytical chemistry. Having sufficiently reliable estimates is important for decision making, e.g., deciding whether a particular measurement method produces results that are fit for the intended purpose (FFP). In some situations it can be useful to compare these estimates. For example, we may wish to establish whether the MU for an in situ method, where measurements are made directly in the field, is significantly different (one would often expect it to be larger) from that obtained using a more traditional laboratory method. Or we might want to compare the different components of MU (e.g., compare the uncertainty arising from the sampling activity with the uncertainty from the analytical method) thus enabling us to take a cost-effective approach to reducing the overall, or combined MU. Quoted values of MU are only ever estimates however, being subject to their own uncertainties (AMCTB No. 105). This has implications when two values of MU are compared. An example is provided where the sampling and analytical components of MU are compared for measurements of the nitrate concentration in a field of lettuces. It is shown that in this case it would be more cost effective to reduce the sampling component of MU in order to reduce the overall MU.

Investigation of dynamic influences in tilted-wave interferometry

Aspherical and freeform lenses allow for compact optical systems and have therefore gained high interest in optics. The interferometric measurement of these forms is a challenge, for which the tilted-wave interferometer (TWI) has been developed. To evaluate the measurement uncertainty of the TWI, both the static and the dynamic influence parameters have to be investigated. In this work, we focus on the dynamic influences on the measurement data of the interferometer. To this end, the individual influences as well as their point of insertion into the process chain are identified. Then the measurement of the interferogram data is modelled as a Monte Carlo simulation. The propagation of different influences through the data process chain to the optical path length differences (OPDs) is also simulated, and the resulting variation of the OPDs is estimated. Furthermore, the variation of the OPDs resulting from measured interferogram data is investigated for comparison. The analysis and quantification of variation of the OPDs along with its contributing influence sources are important steps on the way towards a full uncertainty estimation of optical form measurement with the TWI.

Numerical and Experimental Estimation of Measurement Uncertainty in Magnetic Field Mapping

Numerical and Experimental Estimation of Measurement Uncertainty in Magnetic Field Mapping

Ensuring accurate characteristics of the pipe-piston installation

The study aims to increase the efficiency of the use of the pipe-piston unit by ensuring the reliability of the measurement results based on the development of calibrating technique for the pipe-piston installation. Theoretical research is based on using the principles of system and process approaches. To solve the scientific problem, the fundamental provisions of statistical methods and experimental methods were used; methods of mathematical modeling of estimation of measurement uncertainties. Based on the results of the work, the normative document “Metrology. Installations of a standard pipe-piston. Calibration technique”. The approach to controlling metrological characteristics of the pipe-piston installation, based on estimating the uncertainty of measurements during its calibration, was further developed. Application of the proposed approach allows one to control the metrological characteristics directly on site without disrupting the working product’s accounting process and increasing the pipe-piston installation’s efficiency by an increase in the reliability of measurements and ensuring repeatability.

Development, Validation, and Estimation of Measurement Uncertainty for the Quantitative Determination of Nitrosamines in Sartan Drugs Using LC-APCI-MS/MS

Development, Validation, and Estimation of Measurement Uncertainty for the Quantitative Determination of Nitrosamines in Sartan Drugs Using LC-APCI-MS/MS

Application of systems thinking to the establishment of metrological traceability chains

International agreements in the field of metrology and accreditation of calibration laboratories are the basis for establishing global metrological traceability. Important elements of metrological traceability are calibration of measurement standards and measuring instruments, assessment of measurement uncertainty. The International Laboratory Accreditation Cooperation has a specific policy regarding on traceability of measurement results and estimation of measurement uncertainty in calibration.&#x0D; The partial concept diagram around metrological traceability in accordance with the International Vocabulary of Metrology is proposed. This diagram contains a total of nine metrological concepts, which have most of the associative relations. There are associative relations between the concept of metrological traceability chain and concepts of metrological traceability, measurement standard, calibration and calibration hierarchy, and through the concept of measurement standard with the concept of measurement uncertainty.&#x0D; Systems thinking to the analysis of state of proposed terminological system around metrological traceability was applied. For construction of generalized metrological traceability chain, all the established properties of the system elements around the terminology system of metrological traceability were taken into account.&#x0D; Generalized metrological traceability chain for different levels of the calibration hierarchy was proposed. The proposed chain can be used to develop appropriate chains for specific areas of measurement. To achieve this, it is necessary to determine the specific measured value, the required measurement uncertainty for different levels of the calibration hierarchy and select the necessary measurement standards. Such schemes should be used in national metrology institutes and calibration laboratories.

Applicability of the long-term uncertainty in measurement (LTUM) method for analytical performance assessment in clinical cytometry laboratories.

BackgroundThe estimation of uncertainty in measurement for quantitative analyses is an international obligation of the ISO15189 standard for laboratories. The most widespread method is the Internal Quality Control and External Quality Assessment (IQC + EQA).MethodsWe compared two methods to assess uncertainty in measurement for the quantification of the number of CD34+ stem cells and of the different lymphocyte subpopulations in blood samples: the IQC + EQA method and the Long‐Term Uncertainty in Measurement (LTUM) method.ResultsWe focused on the CD3+/CD4+ T lymphocyte subpopulation for a target value of 350 CD3+/CD4+/μl. The range in terms of uncertainty in the measurement of 350 CD3+/CD4+ cells/μl with the IQC + EQA method was [292.8; 407.2]. With the LTUM method, the uncertainty was 19.1% of the measured value. This represented a range of [283.2; 416.9].ConclusionsThe relative uncertainty calculated with the LTUM method can be adapted to any level of the measured parameter. IQC and EQA calculate the absolute uncertainty and need a clustering of values at different levels. This clustering can lead to some approximations in the uncertainty in measurement determination, particularly around the cut‐off values. Unlike previous reports, uncertainty values were higher when calculated with the LTUM than with the IQC + EQA method. However, LTUM might be more representative of the daily routine practice with patient samples.

Error and uncertainty estimation in gain measurement of double ridge horn antenna working for 1–18 GHz

Error and uncertainty estimation in gain measurement of double ridge horn antenna working for 1–18 GHz

A Sound Level Meter featured with automatic estimation of the measurement uncertainty

In the area of measuring the environmental noise the equivalent sound pressure level LA,eq is adopted and compared with legal thresholds in order to characterize the site of interest. The paper describes an innovative Sound Level Meter (SLM) able to provide information about the measurand contribution to the measurement uncertainty estimation. This measurement technology is made possible thanks to an approach based on bootstrap method for selecting the suitable measurement episode for an estimation of LAeq. The firmware implementation of the developed SLM is disclosed with reference to a low-cost platform for real-time execution of the proposed methodology. Finally, a metrological characterization of the prototype performed in laboratory is reported as well as the performance comparison with a class 1 SLM in a real scenario. As a result, the smart features of the new SLM may be easily implemented by including commercial devices into the instrument schematics.

Experimental quantification of measurement uncertainty and other verification criteria for analytical test methods

If the measurement produces a numerical result (or the stated result is based on a numerical result), then it is necessary to evaluate the uncertainty of these numerical results. If the test methodology does not provide for a rigorous, metrologically and statistically reliable estimate of measurement uncertainty, the test laboratory should attempt to reasonably assess the uncertainty of the measurement results. This is applicable in the case of test methods both rational and empirical. As well as in the laboratory activities, verification of test methods plays an important role in order to guarantee the competence of the laboratory by checking for the criteria of Kohren, Grabbs and others. In cases where test results are not numerically expressed or based on numerical data (e.g., fit/unsuitable or positive/negative, or based on visual or sensory perceptions or other forms of quality analysis), estimates of uncertainty or other variability of results are not required. Nevertheless, laboratories are advised to have an idea of the variability of the results, if possible. The importance of the uncertainty of qualitative test results is undeniable, as is the fact that the necessary statistical methodology (procedure) exists for the calculations. However, due to the complexity of the issue and the inconsistency in the approaches, it is not currently necessary for laboratories to assess the uncertainty of qualitative test results. However, this issue needs to be considered. The article discusses estimates of uncertainty of analytical measurements taking into account the requirements of regulatory documents. The criteria for verification of measurement methodology based on experimental works are also considered and analyzed.

Triple point measurements for new low- global-warming-potential refrigerants: Hydro-fluoro-olefins, hydro-chloro-fluoro-olefins, and trifluoroiodomethane

The triple point temperature of refrigerants is crucial because it serves as a reference for the lower limit of their use temperature in a refrigeration system. In this study, the triple point temperatures for recently proposed refrigerants with low global warming potential were experimentally determined. Ten hydro-fluoro-olefins, two hydro-chloro-fluoro-olefins, and trifluoroiodomethane were investigated. The triple point temperatures of the refrigerants were determined from the obtained cooling and heating curves. To improve measurement accuracy, measurements were conducted on samples obtained from different companies using two different measurement devices. The measured data were found to be in good agreement within the estimated measurement uncertainty.

Uncertainty of measurement and conformity assessment

Knowledge of the measurement uncertainty of test results is fundamentally important for laboratories, their customers and all parties using and interpreting these results. In conformity assessment, a measurement result is used to decide if an item of interest conforms to a specified requirement. Because of measurement uncertainty, there is always the risk of incorrectly deciding whether or not an item conforms to a specified requirement based on the measured value of a property of the item. Conformity assessment can be quite challenging when the entity measured is so close to the tolerance limits of the specification that its uncertainty, however estimated, critically affects decision-making. In such cases, different decision rules can be used to make statements of conformity. The aim of this paper is to provide a survey of methods for the evaluation of measurement uncertainty in testing, as well as to stress the need for appropriate estimation of measurement uncertainty. This paper also aims to assist testing laboratories in understanding the different decision rules used in conformity assessment and level of risk (such as false accept and false reject) associated with the decision rule employed.

Mass Balance Method for Purity Assessment for Pesticide Analytical Standards

Imazamox, a widely used herbicide, is currently managed by the Pesticide MRLs and Positive List System of the Ministry of Food and Drug Safety, and the development of reliable standard materials for analysis is urgently required. To confirm the reliability of the mass balance method, we measured the purity of the imazamox reference material (RM) certified by an RM producer accredited with ISO Guide 34 and estimated measurement uncertainty. According to this method, the content of structurally similar organic impurities was measured using high-performance liquid chromatographic coupled with ultraviolet (HPLC-UV), and the moisture, volatile impurities, and non-volatile impurities were quantitatively analyzed using a thermogravimetric analyzer (TGA). Purity and measurement uncertainty were calculated based on analysis of the HPLC-UV and TGA results obtained, and the validity of these values was confirmed by comparing with the values provided in the RM certificate.

Pancreatic lipase: why laboratory community does not take enough care of this clinically important test?

Although being the recommended laboratory test to diagnose acute pancreatitis, serum pancreatic lipase (LIP) is among the poorly standardized laboratory tests, and laboratory stakeholders often appear to not take enough care of the quality of its measurements. Here we discuss some important issues that, if not correctly managed and solved, make misdiagnosis of acute pancreatitis by using serum LIP a real possibility. First, the current unavailability of a suitable higher-order reference material to be used as common calibrator should be filled up to definitively improve the inter-method bias. Second, knowledge of the analytical characteristics that may explain the defective performance of LIP assays should be deepened. IVD manufacturers should be more explicit in providing this information, including description of their internal protocol for transferring LIP values from internal references to commercial calibrators. Third, recommended models for accurately estimating measurement uncertainty and reliably defining analytical performance specifications for LIP measurements should be applied. Finally, investments considering alternative options for measuring LIP (e.g., targeted to the development of automated LIP immunoassays) should be warranted. All involved stakeholders (standardization bodies, higher-order reference providers, in vitro diagnostics manufacturers, and laboratory professionals) should contribute to fill the existing gap.

Investigation of contribution of number of trials in Monte Carlo simulation for uncertainty estimation for a pressure balance

It is well established that the estimation of measurement uncertainty is vital for the validation of any measurement and is an essential parameter of quality assurance. Apart from the conventional technique of law of propagation of uncertainty (LPU), which has many limitations, Monte Carlo simulation (MCS) technique has become an essential tool for the estimation of measurement uncertainty in various fields of metrology. The most critical factor in MCS is the generation of random numbers of the input quantities according to their probability distributions. The number of Monte Carlo trials to generate these random numbers significantly affects the results. In particular, the required number of trials is also affected by the parameter for which the uncertainty is to be estimated. Hence, in the current paper, the effect of selection of the number of trials on the random number generation and the resulting output in terms of standard deviation (SD) is investigated for the uncertainty in the effective area of a pneumatic reference pressure standard (NPLI-4) at the CSIR-National Physical Laboratory of India. The simulation results thus obtained are compared amongst themselves, with an adaptive approach as well as with the experimental results. The outcomes are analyzed and discussed in detail.