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Measurement Bias (measurement + bias)

Distribution by Scientific Domains

Medical Sciences	50%

Selected Abstracts

Final Thoughts on Measurement Bias and Differential Prediction

INDUSTRIAL AND ORGANIZATIONAL PSYCHOLOGY, Issue 2 2010
ADAM W. MEADE
In the focal article, we suggested that more thought be given to the concepts of test bias, measurement bias, and differential prediction and the implicit framework of fairness underlying the Cleary model. In this response, we clarify the nature and scope of our recommendations and address some of the more critical comments of our work. [source]

Measurement Bias in the HICP: What do we know and What do we need to know?

JOURNAL OF ECONOMIC SURVEYS, Issue 1 2004
Mark A. Wynne
Abstract. The Harmonized Index of Consumer Prices (HICP) is the primary measure of inflation in the euro area, and plays a central role in the policy deliberations of the European Central Bank (ECB). The ECB defines its Treaty mandate of price stability as ,, a year-on-year increase in the Harmonised Index of Consumer Prices (HICP) for the euro area of below 2%[,] to be maintained over the medium term.' Among the rationales given for defining price stability as prevailing at some positive measured inflation rate is the possibility that the HICP as published incorporates measurement errors of one sort or another that may cause it to systematically overstate the true rate of inflation in the euro area. This paper reviews what currently is known about the scope of measurement error in the HICP. We conclude that given the vague conceptual framework of the HICP, the scant research on price measurement issues in the EU and the ongoing improvements in the HICP, there is very little scientific basis at this time for a point (or even an interval) estimate of a positive bias in the HICP. [source]

Morphometric characterization of murine articular cartilage,Novel application of confocal laser scanning microscopy

MICROSCOPY RESEARCH AND TECHNIQUE, Issue 9 2009
Kathryn S. Stok
Abstract A new technique for characterization of the three-dimensional morphology of murine articular cartilage is proposed. The technique consists of a novel application of confocal laser scanning microscopy (CLSM), where the objective was to develop and validate it for cartilage measurements in murine joints. Murine models are used in arthritis research, because they are well-described for manipulating the disease pathophysiology, facilitating our understanding of the disease, and identifying new targets for therapy. A calibration and reproducibility study was carried out to provide a consistent testing methodology for quantification of murine joints. The proximal tibial condyles from male C57BL/6 mice were scanned using a CLS microscope with an isotropic voxel size of 5.8 ,m. Measurements and analyses were repeated three times on different days, and in a second step the analysis was repeated three times for a single measurement. Calculation of precision errors (coefficient of variation) for cartilage thickness and volume was made. The bias of the system was estimated through comparison with histology. This technique showed good precision, with errors in the repeated analysis ranging from 0.63% (lateral thickness) to 3.48% (medial volume). The repeated analysis alone was robust, with intraclass correlations for the different compartments between 0.918 and 0.991. Measurement bias was corrected by scaling the confocal images to 32% of their width to match histology. CLSM provided a fast and reproducible technique for gathering 3D image data of murine cartilage and will be a valuable tool in understanding the efficacy of arthritis treatments in murine models. Microsc. Res. Tech. 2009. © 2009 Wiley-Liss, Inc. [source]

Final Thoughts on Measurement Bias and Differential Prediction

Comparison of segmentation methods for MRI measurement of cardiac function in rats

JOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 4 2010
Johannes Riegler MSc
Abstract Purpose To establish the accuracy, intra- and inter-observer variabilities of four different segmentation methods for measuring cardiac functional parameters in healthy and infarcted rat hearts. Materials and Methods Six Wistar rats were imaged before and after myocardial infarction using an electrocardiogram and respiratory-gated spoiled gradient echo sequence. Blinded and randomized datasets were analyzed by various semi-automatic and manual segmentation methods to compare their measurement bias and variability. In addition, the accuracy of these methods was assessed by comparison with reference measurements acquired from high-resolution three-dimensional (3D) datasets of a heart phantom. Results Relative inter- and intra-observer variability were found to be similar for all four methods. Semi-automatic segmentation methods reduced analysis time by up to 70%, while yielding similar measurement bias and variability compared with manual segmentation. Semi-automatic methods were found to underestimate the ejection fraction for healthy hearts compared with manual segmentation while overestimating them in infarcted hearts. However, semi-automatic segmentation of short axis slices agreed better with 3D reference scans of a heart phantom compared with manual segmentation. Conclusion Semi-automatic segmentation methods are faster than manual segmentation, while offering a similar intra- and inter-observer variability. However, a potential bias has been observed between healthy and infarcted hearts for different methods, which should also be considered when selecting the most appropriate analysis technique. J. Magn. Reson. Imaging 2010;32:869,877. © 2010 Wiley-Liss, Inc. [source]

Nutritional status in pregnant adolescents: a systematic review of biochemical markers

MATERNAL & CHILD NUTRITION, Issue 2 2007
Victoria Hall Moran
Abstract Adolescent pregnancy is a major public health challenge for many industrialized countries and is associated with significant medical, nutritional, social and economic risk for mothers and their infants. Despite this, relatively little is known about the nutritional status of this population. The aim of this paper was to conduct a systematic review of the current evidence relating to the biochemical markers of nutritional status of pregnant adolescents living in industrialized countries. Six papers were identified that fulfilled the inclusion criteria, the majority of which were conducted in the United States. The studies were of variable quality and most failed to control for potential confounders which may have strongly influenced the findings. Due to limited research, conclusions cannot be drawn about the zinc and calcium status of pregnant adolescents, and data on folate and vitamin B12 status appeared conflicting. There was some consensus among studies, however, to suggest that indicators of anaemia and iron status were compromised in pregnant adolescents, particularly during the third trimester of pregnancy. Chronological age did not appear to influence nutritional status, although there was some evidence to suggest that increasing gynaecologic age may positively influence plasma ferritin levels. Current research is limited by sampling and measurement bias, and research is urgently required to address these limitations. Further consideration should also be made of the influence of the role of socio-economic support on pregnant adolescents' nutritional status. The achievement of improved nutrition in pregnancy among adolescents requires multidisciplinary collaborations of adolescent healthcare providers, academics, professional organizations, policymakers, industry and service users. Only once this is achieved can adolescent nutrition, and adolescent nutrition in pregnancy, be significantly and sustainably optimized. [source]

Bayesian galaxy shape measurement for weak lensing surveys , II.

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2008
Application to simulations
ABSTRACT In this paper, we extend the Bayesian model fitting shape measurement method presented in Miller et al., and use the method to estimate the shear from the Shear TEsting Programme simulations (STEP). The method uses a fast model fitting algorithm that uses realistic galaxy profiles and analytically marginalizes over the position and amplitude of the model by doing the model fitting in Fourier space. This is used to find the full posterior probability in ellipticity. The shear is then estimated in a Bayesian way from this posterior probability surface. The Bayesian estimation allows measurement bias arising from the presence of random noise to be removed. In this paper, we introduce an iterative algorithm that can be used to estimate the intrinsic ellipticity prior and show that this is accurate and stable. We present results using the STEP parametrization that relates the input shear ,T to the estimated shear ,M by introducing a bias m and an offset c: ,M,,T=m,T+c. The average number density of galaxies used in the STEP1 analysis was 9 per square arcminute, for STEP2 the number density was 30 per square arcminute. By using the method to estimate the shear from the STEP1 simulations we find the method to have a shear bias of m= 0.006 ± 0.005 and a variation in shear offset with point spread function type of ,c= 0.0002. Using the method to estimate the shear from the STEP2 simulations we find that the shear bias and offset are m= 0.002 ± 0.016 and c=,0.0007 ± 0.0006, respectively. In addition, we find that the bias and offset are stable to changes in the magnitude and size of the galaxies. Such biases should yield any cosmological constraints from future weak lensing surveys robust to systematic effects in shape measurement. Finally, we present an alternative to the STEP parametrization by using a quality factor that relates the intrinsic shear variance in a simulation to the variance in shear that is measured and show that the method presented has an average of Q, 100 which is at least a factor of 10 times better than other shape measurement methods. [source]