Magnitude Of Measurement Error Research Articles

Inverse determination of thermal conductivity by differential quadrature method

The differential quadrature method (DQM) is employed to inverse determination of thermal conductivity in one-dimensional slab. Several examples including spatially dependent and temperature dependent thermal conductivities are solved to illustrate the accuracy and efficiency of the DQM. The advantages of this approach are that no a priori assumption is made on the functional form of the estimates, and that the estimated thermal conductivity can be obtained directly in the calculating process. Of interest are the effects of the number of the measurement points and magnitude of measurement errors on the accuracy of the estimations. Comparisons are made between the estimated thermal conductivities and exact forms, and the agreement is found out to be generally good. Numerical results demonstrate that the DQM is effective and stable in treating this type of problem.

Anthropometric Precision and Accuracy of Digital Three-Dimensional Photogrammetry

A variety of commercially available three-dimensional (3D) surface imaging systems are currently in use by craniofacial specialists. Little is known, however, about how measurement data generated from alternative 3D systems compare, specifically in terms of accuracy and precision. The purpose of this study was to compare anthropometric measurements obtained by way of two different digital 3D photogrammetry systems (Genex and 3dMD) as well as direct anthropometry and to evaluate intraobserver precision across these three methods. On a sample of 18 mannequin heads, 12 linear distances were measured twice by each method. A two-factor repeated measures analysis of variance was used to test simultaneously for mean differences in precision across methods. Additional descriptive statistics (e.g., technical error of measurement [TEM]) were used to quantify measurement error magnitude. Statistically significant (P < 0.05) mean differences were observed across methods for nine anthropometric variables; however, the magnitude of these differences was consistently at the submillimeter level. No significant differences were noted for precision. Moreover, the magnitude of imprecision was determined to be very small, with TEM scores well under 1 mm, and intraclass correlation coefficients ranging from 0.98 to 1. Results indicate that overall mean differences across these three methods were small enough to be of little practical importance. In terms of intraobserver precision, all methods fared equally well. This study is the first attempt to simultaneously compare 3D surface imaging systems directly with one another and with traditional anthropometry. Results suggest that craniofacial surface data obtained by way of alternative 3D photogrammetric systems can be combined or compared statistically.

Adaptive support vector regression analysis of closed-loop inspection accuracy

This study investigates how closed-loop measurement error in CNC milling relates to two different inspection techniques. The on-line inspection of machining accuracy using a spindle probe has an inherent shortcoming because the same machine that produced the parts is used for inspection. In order to use the spindle probe measurement as a means of correcting deviations in machining, the magnitude of measurement errors needs to be quantified. The empirical verification was made by conducting three sets of cutting experiments at the state-of-the-art Cincinnati Arrow Vertical Machining Center. Three different material types and parameter settings were selected to simulate a diverse cutting condition. During the cutting, the cutting force and spindle vibration sensor signals were collected and a tool wear was recorded using a computer vision system. The bore tolerance was gauged by a spindle probe as well as a coordinate measuring machine. The difference between the two measurements was defined as a closed-loop measurement error and adaptive support vector regression analysis was used to predict these bore difference at various values of the explanatory variables. The results show the potential of improving production efficiency and part quality.

Characterization of closed-loop measurement accuracy in precision CNC milling

This study investigates the closed-loop measurement error in computer numerical controlled (CNC) milling as they relate to the different inspection techniques. The on-line inspection of machining accuracy using a spindle probe has an inherent shortcoming because the same machine-produced parts are used for inspection. In order to use the spindle probe measurement as a means of correcting deviations in machining, the magnitude of measurement errors needs to be quantified. The empirical verification was made by conducting three sets of cutting experiments, followed by a design of experiment with three levels and three factors on a state-of-the-art CNC machining center. Three different material types and parameter settings were selected to simulate a diverse cutting condition. During the cutting, the cutting force and spindle vibration sensor signals were collected and a tool wear was recorded using a computer vision system. The bore tolerance was gauged by a spindle probe as well as a coordinate-measuring machine. The difference between the two measurements was defined as a closed-loop measurement error and the subsequent analysis was performed to determine the significant factors affecting the errors. The analysis results showed the potential of improving production efficiency and improved part quality.

Underestimation of Risk Due to Exposure Misclassification

ABSTRACT Aim. Exposure misclassification constitutes a major obstacle when developing dose-response relationships for risk assessment. A non-differentional error results in underestimation of the risk. If the degree of misclassification is known, adjustment may be achieved by sensitivity analysis. The purpose of this study was to examine the full magnitude of measurement error in determining the prenatal exposure to methylmercury. Materials and methods. We used data from a prospective study of a Faroese birth cohort. Two biomarkers of methylmercury exposure were available, i.e., the mercury concentrations in cord blood and in maternal hair (sampled at the time of parturition). The laboratory imprecision on both chemical analyses was thought to be below 5% (coefficient of variation, CV). As a third exposure parameter, we used the dietary questionnaire response on frequency of whale meat dinners. Factor analysis and structural equation analysis were applied to assess the full extent of the imprecision. Results. The calculated total imprecision much exceeded the known laboratory variation: the CV was 28–30% for the cord-blood concentration and 52–55% for the maternal hair concentration. The dietary questionnaire response was even more imprecise. Conclusions. These findings illustrate that measurement error may be greatly underestimated if judged solely from reproducibility or laboratory quality data. Adjustment by sensitivity analysis is meaningful only if realistic measurement errors are applied. When exposure measurement errors are overlooked or underestimated, decisions based on the precautionary principle will not appropriately reflect the degree of precaution that was intended.

Comparison of virtual population analysis and statistical kill-at-age analysis for a recreational, kill-dominated fishery

We used simulations to compare the distributions of estimation errors for virtual population analysis using forward calculation (FVPA) and three variants of statistical kill-at-age analysis (KAA). The KAA variants assumed constant, time-blocked, and nonadditive selectivity. Simulations were based on a recreational walleye (Sander vitreus) fishery in Lake Mille Lacs, Minnesota. The focus of our experiments was on how model mis-specification (incorrect assumptions about selectivity for KAA or that kill had no error for FVPA) interacted with the magnitude of measurement errors and fishing mortality. We found that KAA models outperformed FVPA when they assumed the correct selectivity pattern, even when kill was measured without error. Of particular concern was a strong tendency by FVPA to overestimate stock size when kill was measured with substantial error. When KAA was based on an incorrect assumption regarding fishery selectivity and kill was measured with little error, wide distributions of errors and substantial biases sometimes resulted. KAA models that allowed fishery selectivity to change over time performed about as well as a constant-selectivity KAA model when selectivity was constant, and they performed much better when selectivity changed over time. Careful consideration of alternative fishery selectivity models should be a fundamental part of any age-structured assessment.

Musculoskeletal responses of 2-year-old Thoroughbred horses to early training. 2. Measurement error and effect of training stage on the relationship between objective and subjective criteria of training workload

AIM: To identify the magnitude and sources of error involved in simply quantifying the workload of a group of Thoroughbred racehorses in training. METHODS: Data were obtained from seven 2-year-old fillies trained for 13 weeks on sand and grass tracks at various cantering velocities, and at the gallop in the last 4 weeks. Four fillies completed training and comprised a ‘high exercise intensity’ subgroup; three fillies did not complete all gallops due to lameness or injury and comprised a ‘medium exercise intensity’ subgroup. The trainer recorded the distance, time, track used, and subjective gait (SG; viz canter, ¼-pace, ½-pace and gallop) of each horse each day. Data were analysed to describe the training programme and sources of variation in workload. A cumulative workload index (CWI) was devised to simply express distance and velocity aspects of the training programme. RESULTS: The magnitude of errors in measurement of timing and distance were small but significant (<0.8%, p=0.01). SG was an inaccurate descriptor of velocity. Mean velocity of ½-pace decreased from 8.92 (SE 0.049) in Weeks 6–8 to 6.33 (SE 0.061) m/sec after the start of galloping sessions in Week 9 (p=0.01). Track surface had a significant effect on the velocity of ½-pace (p=0.001). The fastest velocity was recorded on the grass (9.06, SE 0.292 m/sec), followed by ‘plough’ (8.23, SE 0.152 m/sec), and sand (7.90, SE 0.132 m/sec) tracks. The CWI of the horses ranged between 1,085,000 and 1,634,000 (mean=1,428,000; SE 78,000). The average exercise intensity per week was 110,000 (SE 1,048). There were no significant differences between high and medium exercise intensity subgroups for the canter and ¼-pace. The high exercise subgroup had a greater CWI for the ½-pace (839,000 vs 559,000; p=0.004), gallop (71,000 vs 31,000; p=0.001), and total index (1,580,000 vs 1,242,000; p=0.001). CONCLUSIONS: The workload history of a horse can be accurately described using an index based on manual measurement of the time and distance worked. CLINICAL RELEVANCE: Accurate and precise data on the training programme of performance horses are likely to enable greater differentiation of aspects of workload which are associated with both performance and injury.

Identification of velocity distribution in a turbulent flow inside parallel-plate ducts from wall temperature measurements

An Inverse Heat Convection Problem is investigated in this numerical study. Turbulent forced convection is considered, with a hydrodynamically fully developed, thermally developing, incompressible, constant property flow inside a parallel-plate duct. Velocity and effective diffusivity distributions of the turbulent model are characterised by a Reynolds number b + based on the shear stress velocity. The identification of b + from simulated wall temperature measurements is presented. A heat flux density is applied along the channel length and temperature responses are taken at the wall external surface. Heat transfer has to act as a small but measurable perturbation of the flow. The inverse problem is recast into an optimisation problem solved with a Quasi-Newton method. Reynolds numbers 105 and 106, corresponding to two different values of b + , are considered. Effects of sensor number and location, as well as magnitude of measurement error on the estimation accuracy, are examined.

Nondestructive Evaluation Method of Welding Residual Stresses by Heating Method

In this paper, a new method of estimating welding residual stresses nondestructively is presented. From the strain changes on the surface due to the local change of Young modulus, distributions of eigenstrain are determined by the inverse analysis. Residual stresses are then evaluated by the elastic FEM analysis by using the eigenstrain as initial condition. Since the local change of Young modulus are due to temperature dependency by heating, we refered to the method as heating method. The method is used to estimate the residual stress distribution in a plate formed by joining two sections with a butt weld. The results show that the proposed method is robust, efficient and accurate. In this procedure, the simulated measured strains are generated by adding random error to the strain response form the solution of the direct solution, and the singular value decomposition method is used as a regularization method. The effects of number of sensors and their locations, the magnitude of measurement errors on the accuracy of estimations are investigated.

Wage rentals for reproducible human capital: evidence from Ghana and the Ivory Coast

Education, child nutrition, adult health/nutrition, and labor mobility are critical factors in achieving recent sustained growth in factor productivity. To compare the contribution of these four human capital inputs, an expanded specification of the wage function is estimated from household (LSMS) surveys of the Ivory Coast and Ghana. Specification tests assess whether the human capital inputs are exogenous, and instrumental variable techniques are used to estimate the wage function. Smaller panels from the Ivory Coast imply the magnitude of measurement error in the human capital inputs and provide more efficient instruments to estimate the wage equation. The conclusion emerges that weight-for-height and height are endogenous, particularly prone to measurement error, and heterogeneous in their effects on wages. Overall returns to these four forms of human capital are similar within each country for men and women, but education and migration returns are higher in the more rapidly growing Ivory Coast, and the wage effects of child nutrition proxied by height are greater in poorer, more malnourished Ghana.

Poster 3: Three-dimensional scapular attitudes measured with the optotrak probing system: a reliability study on 30 shoulders

Objective: To evaluate the intra- and intersessions reliability of 3-dimensional scapular attitudes measured with a new method. Design: Test-retest. Setting: 2 sessions with the same protocol repeated by the same evaluator. Participants: 15 healthy subjects (30 shoulders). Interventions: 3-dimensional scapular attitudes were measured at 70° of flexion, 90° of abduction, and arm at rest, using the Optotrak probing system. 3 trials were recorded for each position. For each trial, the posterolateral tip of the acromion, the inferior angle, and the edge of the spine of the scapula were digitized. Main Outcome Measure: 3-dimensional scapular attitudes in external and internal rotation, anterior and posterior tilting, and anterior and posterior transverse rotation planes. Results: The intrasession reliability at 70° of flexion and 90° of abduction was excellent, as indicated by intraclass correlation coefficients (ICCs), which ranged from .87 to .99, and standard errors (SEs) of measurement, which varied from 0.4° to 1.7°. The intersessions reliability was poorer, with ICCs ranging from .37 to .56, and SEs of measurement varying from 2.7° to 4.7°. Conclusion: For studies that look at the effect of rehabilitation interventions on 3-dimensional scapular attitudes, findings should be interpreted in light of the magnitude of measurement errors.

The Reliability of Measuring Neck Muscle Strength with a Neck Muscle Force Measurement Device.

The purpose of this study was to examine the reliability of an isometric neck muscle force measurement device. Thirty-five healthy non-athlete subjects (18 males and 17 females, aged 19-30) participated in this study. The maximal isometric muscle strength of the neck extensor and flexor muscles were measured at different times and on different days using a newly designed neck muscle force measurement apparatus. On each occasion, subjects performed three maximum voluntary contractions in each direction of neck extension and flexion movement. The interclass correlation coefficient (ICC) and standard deviation within subjects (Sw) were computed to evaluate the reliability and magnitude of measurement error between measurements. The results of the intra-rater, test-retest, and inter-rater reliability (ICCs ≥ 0.94, Sws ≤ 4.9 N) indicate that the neck muscle force measurements were highly repeatable and varied little between measurements. There were no statistically significant differences in neck muscle force measurements between times, between days and between raters. Maximal isometric muscle strengths were significantly higher in males than in females (p < 0.00). Women's neck muscle strengths were 55% and 54% of men in cervical extension and cervical flexion, respectively. The isometric muscle force measurement device which was used in this study appears to be a reliable and useful method for measuring the force of the neck extensor and flexor muscles. It could also be suitable for the assessment of a physiotherapeutic or rehabilitation program.

Error Control in Residue Number Systems

This paper introduces an alternate approach to error control in residue number systems which utilizes sets of moduli that include pairs with non-trivial common factors. Necessary and sufficient conditions for achieving a specified capacity for error detection or correction are derived by considering the minimum Hamming distance of an associated linear code. Effective error-control procedures are developed based on a syndrome matrix whose entries are obtained directly from the residue digits. The potential of a priori bounds on the magnitude of measurement errors to increase the efficiency of the control process is analyzed.

The ability of ratings and choice conjoint to predict market shares: a Monte Carlo simulation

We use a Monte Carlo simulation with many synthetic data sets to compare ratings and choice conjoint analysis in their ability to correctly predict market shares under varying market conditions. Our results provide guidance to researchers seeking to use conjoint analysis for managerial decisions. Our recommendations are quite different from the recommendations of prior researchers who compared conjoint methods using single empirical data sets. Our results indicate that one must, at least roughly, assess the degree of consumers' heterogeneity in preferences, product similarity in the marketplace, typical consumers' choice-rule (probabilistic or deterministic), and magnitude of error in measurement of utilities in order to make a prudent choice between ratings and choice conjoint analysis.

SIMULTANEOUS ESTIMATION OF INLET TEMPERATURE AND WALL HEAT FLUX IN TURBULENT CIRCULAR PIPE FLOW

An inverse heat convection problem is solved for simultaneous estimation of unknown inlet temperature and wall heat flux in a thermally developing, hydrodynamically developed turbulent flow in a circular pipe based on temperature measurements obtained at several different locations in the stream. The direct problem of turbulent forced convection is solved with a finite difference method with appropriate algebraic turbulence modelling. Although we seek for two unknown functions, we formulate the inverse problem as one of parameter estimation through the representation of the unknown inlet temperature profile and the wall heat flux distribution by one-dimensional finite element interpolation. Nodal values of the inlet temperature and the wall heat flux at chosen positions are determined as unknown parameters through the Levenberg–Marquardt algorithm for minimization procedure. Numerical results for several testing cases with different magnitudes of measurement errors are examined by using simulated experimental data. The effects of the number and the locations of the temperature measurement points are discussed.

Revisiting the Reportedly Weak Value Relevance of Oil and Gas Asset Present Values: The Roles of Measurement Error, Model Misspecification, and Time-Period Idiosyncrasy

This paper investigates three potential explanations for the puzzlingly weak value relevance of oil and gas asset present values documented in prior research: measurement error, model misspecification, and time-period idiosyncrasy. I operationally define the magnitude of measurement error as the measurement error variance, estimated using an errors-in-variables two-stage regression model similar to that used by Barth (1991) and Choi et al. (1997). I find that (1) measurement error in the present value measure of oil and gas assets is on average less than the measurement error in the historical cost asset measure; (2) oil and gas assets measured at present value explain significantly more across-firm and across-time variation in stock prices than do oil and gas assets measured at historical cost; and (3) model misspecification partially accounts for the puzzlingly weak reported value relevance of the present value measure in prior research.

Revisiting the Reportedly Weak Value Relevance of Oil and Gas Asset Present Values: The Roles of Measurement Error, Model Misspecification, and Time Period Idiosyncrasy

This paper investigates three potential explanations for the puzzlingly weak value relevance of oil and gas asset present values documented in prior research: measurement error, model misspecification, and time-period idiosyncrasy. I operationally define the magnitude of measurement error as the measurement error variance, estimated using an errors-in-variables two-stage regression model similar to that used by Barth (1991) and Choi et al. (1997). I find that (1) measurement error in the present value measure of oil and gas assets is on average less than the measurement error in the historical cost asset measure; (2) oil and gas assets measured at present value explain significantly more across-firm and across-time variation in stock prices than oil and gas assets measured at historical cost; and (3) model misspecification partially accounts for the puzzlingly weak reported value relevance of the present value measure in prior research.

Uncertainties of Monod kinetic parameters nonlinearly estimated from batch experiments.

Monod kinetic parameters (Ks, micromax, and Y) that are estimated from batch experimental data can have large uncertainties due to linear correlations between them. The degree of correlation and the resulting uncertainties of the Monod parameters are functions of the initial experimental conditions, the values of the parameters, the type and magnitude of measurement errors, and the sampling number. Careful manipulation of experimental conditions can reduce the correlations between Monod parameters allowing for the estimation of Monod kinetic parameters with the lowest degree of uncertainty. By dimensionless analysis, the correlation and relative standard deviations of Monod parameters were found to be functions of a few dimensionless variables involving the initial substrate (S0) and cell (X0) concentrations. Quantitative relationships were analyzed between the dimensionless variables and the correlation and the uncertainties of the Monod parameters. This analysis allowed for identification of the optimal experimental conditions for estimating Monod parameters under both no growth and growth conditions coupled with two kinds of measurement errors: those with constant absolute standard deviation and those with constant relative standard deviation. Examples involving the microbial reduction of iron(III) as an electron acceptor are used to illustrate the application of the developed technique.

Precision of quantitative ultrasound measurement of the heel bone and effects of ambient temperature on the parameters.

The goal of this study was to determine the magnitude of measurement error of a quantitative ultrasound (QUS) measurement system of the heel bone in a practical setting and to examine the effects of ambient temperature in the test room on QUS parameters. We assessed the intratest, intertest and interdevice coefficients of variation (CVs) for speed of sound (SOS), broadband ultrasound attenuation (BUA) and stiffness in vitro using phantoms and in vivo using volunteers. The intratest CV was the smallest and the interdevice CV was the greatest for every QUS parameter. The intertest CVs in vivo were 0.50% for SOS, 2.53% for BUA and 4.38% for stiffness. The standardized precision error (sPE) of stiffness, however, was smaller than those of the other two parameters. The intertest sPEs in vivo of the QUS parameters were 2-3 times greater than that of the spine bone mineral density (BMD) as measured by dual-energy X-ray absorptiometry (DXA). Using an average of duplicate measurements for the representative value of a subject could improve sPE of the QUS parameters to around 2 times greater than that of spine BMD. We examined five phantoms each with the QUS system under the ambient temperature conditions of 10, 20 and 30 degrees C. The lower the room temperature, the greater the values of all the QUS parameters obtained. We then assessed the effect of the season on the QUS parameters in healthy five women. SOS and stiffness were significantly greater in February (room temperature, 12.6 degrees C) than in June (22.4 degrees C) by 0.74% and 3.2% of overall means, respectively, by 10.1% and 4.3% as a standardized difference, or by 0.422 and 0.214 in Z-scores. This difference was likely to be caused by the difference in heel temperature between the seasons. The precision of the QUS system was inferior to that of conventional DXA densitometry. We recommend that institutions using several QUS system devices throughout the year at various locations monitor the precision of each device, make duplicate measurements for a single subject, use the same device for each patient being followed, and control the heel temperature of subjects by keeping the test room temperature constant throughout the year.

A 2-D INVERSE METHOD FOR SIMULTANEOUS ESTIMATION OF THE INLET TEMPERATURE AND WALL HEAT FLUX IN A LAMINAR CIRCULAR DUCT FLOW

A two-dimensional inverse analysis is presented for the estimation of the inlet temperature of the fluid flow and wall heat flux in a thermally developing hydrodynamically developed laminar flow in a duct. The inverse analysis is based on the temperature reading located at a stream inside the duct at several different points. At the beginning of the study, finite difference methods are employed to discretize the problem, and then a linear inverse model is constructed to identify the unknown conditions. The present approach is to rearrange the matrix forms of the differential governing equation and estimate the inlet temperature of the fluid and unknown surface conditions of the duct. The linear least squares method is adopted to find the solution. The advantage of applying this method in inverse analysis is that no prior information is needed on the functional form of the unknown quantities, no initial guess is required, and the number of iterations in the calculation process is limited to one. The effects of sensor position, magnitude of measurement error, and number of measurements on the accuracy of estimates are examined. The results show that the preferred position of the sensor is closer to the inlet region and only few measuring points are sufficient to estimate the wall heat flux and inlet temperatures of the fluid when the measurement errors are neglected. When the measurement errors an considered, more measuring points are needed in order to increase the congruence of the estimated results to exact solutions.