Unit conversion as a source of misclassification in US birthweight data. (1/19)

OBJECTIVES: This study explains why frequency polygons for US birthweights in 100-g weight classes appear spiky compared with their European counterparts. METHODS: A probability model is used to describe how unit conversion can induce misclassification. Birthweights from the United States and Norway are used to illustrate that misclassification operates in grouped US data. RESULTS: Spikiness represents misclassification that arises when measured birthweights are rounded to the nearer ounce, converted to grams, and then grouped into weight classes. Misclassification is ameliorated, not eliminated, with 200-g weight classes. CONCLUSIONS: Possible biases from misclassification should be carefully evaluated when fitting statistical models to grouped US birthweights.  (+info)

Human and automatic face recognition: a comparison across image formats. (2/19)

Human subjects perform poorly at matching different images of unfamiliar faces. When images are taken by different capture devices (cameras), matching is difficult for human perceivers and also for automatic systems. We test an automatic face recognition system based on principal components analysis (PCA) and compare its performance with that of human subjects tested on the same set of images. A number of variants of the PCA system are compared, using different matching metrics and different numbers of components. PCA performance critically depends on the choice of distance metric, with a Mahalanobis metric consistently outperforming a Euclidean metric. Under optimal conditions, the automatic PCA system exceeds human performance on the same images. We hypothesise that unfamiliar face recognition may be mediated by processes corresponding to rather simple functions of the inputs.  (+info)

Restructuring nuclear regulations. (3/19)

Nuclear regulations are a subset of social regulations (laws to control activities that may negatively impact the environment, health, and safety) that concern control of ionizing radiation from radiation-producing equipment and from radioactive materials. The impressive safety record among nuclear technologies is due, in no small part, to the work of radiation safety professionals and to a protection system that has kept pace with the rapid technologic advancements in electric power generation, engineering, and medicine. The price of success, however, has led to a regulatory organization and philosophy characterized by complexity, confusion, public fear, and increasing economic costs. Over the past 20 years, regulatory costs in the nuclear sector have increased more than 250% in constant 1995 U.S. dollars. Costs of regulatory compliance can be reduced sharply, particularly when health and environmental benefits of risk reduction are questionable. Three key regulatory areas should be closely examined and modified to improve regulatory effectiveness and efficiency: a) radiation protection should be changed from a risk-based to dose-based system; b) the U.S. government should adopt the modern metric system (International System of Units), and radiation quantities and units should be simplified to facilitate international communication and public understanding; and c) a single, independent office is needed to coordinate nuclear regulations established by U.S. federal agencies and departments.  (+info)

Experience with SI units in biochemistry. (4/19)

Use of Systeme International d'Unites (SI) for laboratory measurements was instituted Jan. 1, 1975 at two community hospitals. Beforehand, talks were given, pamphlets, conversion tables, new calibration curves and new master record cards were printed, computer cards were reprogrammed and conversion kits were prepared; the total cost was less than $200. After 6 months 16% of the medical staff had stopped converting SI units into conventional units, 78% were still occasionally converting units and 6% were routinely converting units. Changeover had been difficult for 25%, only a nuisance for 49% and easy for 26%. The patients' lives were not endangered by conversion.  (+info)

A new equivalence based metric for predictive check to qualify mixed-effects models. (5/19)

The main objective of any modeling exercise is to provide a rationale for effective decision making during drug development. The aim of the current simulation experiment was to evaluate the properties of predictive check as a covariate model qualification technique and, more importantly, to introduce and evaluate alternative criteria to qualify models.Original concentration-time profiles (yod) were simulated using a 1-compartment model for an intravenous drug administered to 25 men and 25 women. The typical clearance for male subjects (TVCLm) was assumed to be 5-fold higher than that for female subjects (TVCLf). Fifty such trials under the same design were generated randomly. Predictive check was used as the model qualification tool to study predictive performance of true (males not equal females) and false (males = females) models in the context of maximum likelihood estimation. For each yod, 200 replications were generated to study the properties of a discrepancy variable, a statistic that depends on the model, and a test statistic, a statistic that does not depend on the model. Several qualification criteria were evaluated in assessing predictive performance, such as, predictive p-value (Pp), probability of equivalence (peqv), and probability of rejecting the null hypothesis (data = model) using the Kolmogorov-Smirnov test (pks). The Pp value was calculated using sum of squared errors as a discrepancy variable. For both of the models, the Pp values uniformly ranged between 0 and 1. The pattern of Pp values suggests that qualification of the false model is unlikely. For both of the models, the range of peqv is about 0.95 to 1.0 for concentration at 0.5 hours. However, this is not the case for the concentration at 4 hours, which is primarily dependent on the clearance. The false model (0.35 to 0.50) has poor predictive performance compared with the true model (0.65 to 0.80) using peqv. The pks suggests no difference in the distributions of replicated and original concentrations at all of the time points for both of the models. Discrepancy variables cannot aid in rejecting false models, whereas the use of a test statistic can aid in rejecting false models. However, selection of an informative test statistic is challenging. As far as the qualification criteria are considered, the equivalence-based comparison of a test statistic is more informative than a significance-based comparison. No convincing evidence exists in the literature demonstrating the added advantages of predictive check as a routine model qualification tool over the existing tools, such as diagnostic plots or mechanistic reasoning. However, when a model is to be used for designing a trial, it should at least be able to regenerate the data used to build the model. In such cases, predictive check might offer insights into potential inconsistencies.  (+info)

Universal metrics for quality assessment of protein identifications by mass spectrometry. (6/19)

Increasing numbers of large proteomic datasets are becoming available. As attempts are made to interpret these datasets and integrate them with other forms of genomic data, researchers are becoming more aware of the importance of data quality with respect to protein identification. We present three simple and universal metrics that describe different aspects of the quality of protein identifications by peptide mass fingerprinting. Hit ratio gives an indication of the signal-to-noise ratio in a mass spectrum, mass coverage measures the amount of protein sequence matched, and excess of limit-digested peptides reflects the completeness of the digestion that precedes the peptide mass fingerprinting. Receiver-operating characteristic plots show that the novel metric, excess of limit-digested peptides, can discriminate between correct and random matches more accurately than search score when validating the results from a state-of-the-art protein identification software system (Mascot) especially when combined with the two other metrics, hit ratio and mass coverage. Recommendations are made regarding the use of the metrics when reporting protein identification experiments.  (+info)

Proposal for a nomenclature for magnetic resonance imaging based measures of articular cartilage in osteoarthritis. (7/19)

OBJECTIVE: Magnetic resonance imaging (MRI) of articular cartilage has evolved to be an important tool in research on cartilage (patho)physiology and osteoarthritis (OA). MRI provides a wealth of novel and quantitative information, but there exists no commonly accepted terminology for reporting these metrics. The objective of this initiative was to propose a nomenclature for definitions and names to be used in scientific communications and to give recommendations as to which minimal methodological information should be provided when reporting MRI-based measures of articular cartilage in OA. METHODS: An international group of experts with direct experience in MRI measurement of cartilage morphology or composition reviewed the existing literature. Through an iterative process that included a meeting with a larger group of scientists and clinicians (December 2nd, 2004, Chicago, IL, USA), they discussed, refined, and proposed a nomenclature for MRI-based measures of articular cartilage in OA. RESULTS: The group proposes a nomenclature that describes: (1) the anatomical location and (2) the structural feature being measured, each name consisting of a metric variable combined with a tissue label. In addition, the group recommends minimal methodological information that should be described. CONCLUSIONS: Utilization of this nomenclature should facilitate communication within the scientific community. Further, the uniform adoption of comprehensive nomenclature to describe quantitative MRI- features of articular cartilage should strengthen epidemiological, clinical, and pharmacological studies in OA.  (+info)

Reliability and accuracy of cirtometry in healthy adults. (8/19)

OBJECTIVE: To determine the intrarater and interrater reliability of cirtometry (measurements of the circumference of the chest and abdomen taken during respiratory movements) as well as its correlation with pulmonary volumes measured by respiratory inductive plethysmography. METHODS: A total of 40 healthy individuals were evaluated. The mean age was 28 years. The measurements were taken in the supine position at three different time points: at rest, at maximal inspiration, and at maximal expiration. Two trained investigators, each of whom was blinded as to the results obtained by the other, performed the measurements. The Friedman test was used to determine intrarater reliability, and the Wilcoxon test, together with the intraclass correlation coefficient, were used to determine interrater reliability. The correlation between the cirtometry measurements and the plethysmography results was obtained using Spearman's correlation coefficient. The level of significance was set at 0.05 for all tests. RESULTS: Intrarater reliability was satisfactory. Regarding interrater reliability, statistically significant differences (2.8 cm at the most) were found in all sets of measurements. However, through the analysis of the intraclass correlation coefficient, the investigators were found to be responsible only for a small portion of the variability (1.2-5.08%) found among the measurements. When the cirtometry measurements were compared to the volumes measured by respiratory inductive plethysmography, low correlations (range, r = 0.170-0.343) were found. CONCLUSIONS: The findings of this study suggest that, although cirtometry is a reliable measurement, it does not accurately measure pulmonary volumes.  (+info)

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