Standard Deviation Of Measurement Error Research Articles

Age is not just a number: How incorrect ageing impacts close-kin mark-recapture estimates of population size.

Population size is a key parameter for the conservation of animal species. Close-kin mark-recapture (CKMR) relies on the observed frequency and type of kinship among individuals sampled from the population to estimate population size. Knowledge of the age of the individuals, or a surrogate thereof, is essential for inference with acceptable precision. One common approach, particularly in fish studies, is to measure animal length and infer age using an assumed age-length relationship (a 'growth curve'). We used simulation to test the effect of misspecifying the length measurement error and the growth curve on population size estimation. Simulated populations represented two fictional shark species, one with a relatively simple life history and the other with a more complex life history based on the grey reef shark (Carcharhinus amblyrhynchos). We estimated sex-specific adult abundance, which we assumed to be constant in time. We observed small median biases in these estimates ranging from 1.35% to 2.79% when specifying the correct measurement error standard deviation and growth curve. CI coverage was adequate whenever the growth curve was correctly specified. Introducing error via misspecified growth curves resulted in changes in the magnitude of the estimated adult population, where underestimating age negatively biased the abundance estimates. Over- and underestimating the standard deviation of length measurement error did not introduce a bias and had negligible effect on the variance in the estimates. Our findings show that assuming an incorrect standard deviation of length measurement error has little effect on estimation, but having an accurate growth curve is crucial for CKMR whenever ageing is based on length measurements. If ageing could be biased, researchers should be cautious when interpreting CKMR results and consider the potential biases arising from inaccurate age inference.

Direct reconstruction of the temperature field of lithium-ion battery based on mapping characteristics

Lithium-ion (Li-ion) batteries are susceptible to the working temperature so that the monitoring is essential to the battery internal temperature. The electrochemical-thermal coupling model completely reflects the battery internal behavior. However, the high complexity and multi-field coupling make it difficult to be applied to reconstruct the battery temperature field based on state observer. Based on mapping characteristics, this work proposes a temperature field direct reconstruction scheme. And the electrochemical-thermal coupling model plays a large role in this scheme. Mapping characteristic vectors of the transient temperature field are obtained from the step response model of the Li-ion battery temperature field to charge and discharge current. Furthermore, the quantitative connection of the mapping characteristic vectors between the surface points of and the internal nodes of the battery is characterized by a relevance degree matrix. And a direct reconstruction model of the internal transient temperature field is established. The internal temperature field is reconstructed directly online and in real time via exploiting the temperature measurements on battery surface. In numerical experiments, the three-dimensional temperature field of the Li-ion battery charge and discharge processes is reconstructed. The effects of charge and discharge rates, model mismatch, and measurement errors on the reconstruction results are investigated. During the charge and discharge processes, the maximum values of the transient average error of the reconstructed temperature field are about 0.4 K and 0.3 K, respectively. And the transient average error is generally below 0.8 K when the standard deviation of measurement errors is 0.5 K.

Accuracy comparison of terrestrial and airborne laser scanning and manual measurements for stem curve-based growth measurements of individual trees

Monitoring forest growth accurately is important for assessing and controlling forest carbon stocks that impact, for example, the atmospheric CO2 concentration and, consequently, the climate change. In prior studies, forest growth monitoring with laser scanning methods has resulted in relatively high errors. However, the contribution of reference measurement error to uncertainty in growth resolution has rarely been analysed, and the reference measurements are usually considered mostly flawless. In this study, a seven-year-long growth of individual trees was estimated using both airborne and terrestrial laser scanning (ALS, TLS) that have emerged as potential candidates for digital forest reference measurements. The growth values were derived for diameter at breast height (DBH) and stem volume between the years 2014 and 2021 using an indirect approach. The values obtained with laser scanning were paired with manual field measurements and also with each other to study pairwise errors. The pairwise comparison showed that even though all the three measurement methods produced good Pearson correlation coefficients for one-time measurements (all above 0.88), the coefficients for growth measurements were significantly lower (0.19–0.44 for DBH and 0.47–0.66 for stem volume). The best correlation and root mean squared deviation (RMSD) for DBH growth (ρ = 0.44, RMSD = 0.98 cm) and stem volume growth (ρ = 0.66, RMSD = 0.052 m3) was observed between the manual field measurements and the ALS-based growth measurement method, in which the tree stem curve was obtained from the 2021 point cloud, and the stem curve was predicted backwards for the year 2014 according to height growth. The ALS method suffered less from outlying values than the TLS-based growth measurement method, in which the growth was computed based on the difference of stem curves derived separately for the years 2014 and 2021. The study showed that observing the stem curve is a potential method for short-period growth monitoring. Using the pairwise comparison results, we further derived estimates for the mean and standard deviation of measurement error of each individual measurement method. For the manual measurements, the standard deviation of error was found to be approximately 0.4 cm for DBH growth and 0.03 m3 for volume growth, which were the lowest of the three methods but not by a large margin. This highlights the need for more accurate reference data as the accuracy of laser scanning-based growth estimation methods continues to approach the accuracy of manual measurements.

Accuracy of photoplethysmography-based measurement of blood pressure

Abstract Funding Acknowledgements Type of funding sources: None. Introduction Photoplethysmography (PPG)-based blood pressure (BP) measurements are available in the latest smartwatches and are thus available for patients in the consumer market. While the devices typically comply with the medical device regulation, accuracy is often not known and data on validation are not publicly available. Purpose To investigate the accuracy and precision of the Samsung Galaxy Watch Active 2 PPG-based BP measurement as compared to conventional BP measurement and to investigate clinical applicability. Methods 31 patients scheduled for ambulatory 24-hour BP measurement were included in the study. 24-hour BP devices were attached to the non-dominant arm, smartwatches were attached to the opposite arm. Calibration was performed as instructed by the manufacturer. The smartwatch was used to register BP intermittently for 24 hours. Results from both devices were compared using the Taffé method. Results and discussion Mean age was 59 years. 17 patients (55%) were male. Comparison of the two methods is demonstrated in Figure 1. The smartwatch overestimates the systolic BP up to approximately 132 mm Hg and then underestimates the systolic BP, illustrating the presence of proportional (0.48) and differential (69.0) bias. Precision for the gold standard method was higher compared to the smartwatch measurements. For increasing values of systolic BP, the precision of the smartwatch decreases. For diastolic BP, differential (31.4) and proportional bias (0.68) are present, resulting in an overestimation of the diastolic BP at lower values (<100 mmHg). Precision for the gold standard method was higher at lower BP values, while precision for smartwatch measurements was higher at higher BP values (i.e. there was a lower standard deviation of measurement error). Figure 1 Bias and precision plots for systolic and diastolic blood pressure (BP). In each figure the x-axis indicates the best linear unbiased prediction (BLUP) or true value of BP. Panel A and B indicate the bias plots. Smartwatch measurements (blue dashed lines) are compared to reference measurements (solid black line); both values are read from the leftmost y-axis. The bias (difference of smartwatch measurement compared to the reference method) is depicted as a solid red line; the value of bias is read from the rightmost y-axis. Panel C and D indicate the precision plots, indicating the standard deviation of measurement errors for both measurement methods. The reference method is depicted in black; the smartwatch method is depicted in blue. Conclusion There is a differential and proportional bias in PPG-based BP measurement of systolic and diastolic BP measurement. The systolic BP is overestimated at lower values and underestimated at higher values. This might indicate potential for application as a screening tool for hypertension. Further research is needed to investigate clinical applicability.

A general topology identification framework for distribution systems using smart meter and μ-PMU measurements

To enhance topology observability of the power distribution network (PDN), a general topology identification framework using multiple measurement data records of nodal voltages and currents is constructed in this paper. The framework includes three topology identification approaches to handle different situations. The first approach describes a modified three-stage heuristic procedure for the single topology identification while leveraging the sparsity feature of the nodal admittance matrix, which can lead to more accurate identification results than the base model in the literature; The second approach presents a multi-topology identification model to process the measurement data set with a given number of topologies, which classifies records into a fixed number of topology categories and then determines the nodal admittance matrix for each topology category; The third approach designs a two-stage procedure for the measurement data set containing an unknown number of topologies, which determines the number of topologies, the record classification, and the nodal admittance matrices of individual topologies. Effectiveness of the proposed models in efficiently identifying the PDN’s topologies is illustrated via several cases, with measurement data sets containing a given or an unknown number of topologies. In addition, the sensitivity analysis quantifies the influence of the number of records, the standard deviation of measurement errors, and the pre-specified maximum number of nonzero elements in each column of the nodal admittance matrix on the accuracy of the identification results.

Estimation of the CHSH Parameter Using HOM Interference

The Clauser–Horne–Shimony–Holt (CHSH) experiment is an essential test of nonlocality in quantum mechanics and can be used to validate the principle of entanglement. In addition to verifying entanglement, the measurable CHSH parameter can also be used to gauge the quality of the entanglement present in a system. The measurement of Hong–Ou–Mandel (HOM) interference is another important fundamental experiment in quantum optics that measures the indistinguishability of a pair of photons. In this article, we demonstrate how the results of a HOM interference experiment, a relatively simple experiment, can be used to obtain an estimate for the value of the CHSH <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$S$</tex-math></inline-formula> parameter, which is a more complicated measurement. We experimentally demonstrate that the HOM interference technique is capable of providing an estimate of the value of the CHSH parameter that is within one standard deviation of measurement error when spectral impairments are present. We expect that this technique will aid in the calibration of quantum optical systems.

Determining the Accuracy of Measuring the Heights of Objects in the Automatic Processing of Stereo Images

Introduction. Currently, information on the spatial description of objects is used in many areas of human activity. One of these types of information are the coordinates of the objects. These data are used in cartography, the construction of digital maps and 3D models, for the operation of the navigation means, etc. There are many software for design and analysis of digital elevation models. These are modules and packages like Spatial Analyst, 3D Analyst, ArcGIS packages, program MapInfo (MapInfo Corp.), Autodesk Map 3D of AutoCAD (Autodesk Inc.) and others. Common to them is build automation of soprovich terrain models, including the combination of the images of the stereopair, what is necessary to measure heights of objects for automated creation of digital elevation models of the earth's surface one of the key quality indicators is the accuracy of determining the heights of objects. The main influence on this indicator provides measurement error of parallax when processing stereosystem. Obtaining analytical expressions for the accuracy of the determination of the height of the object. To obtain the formula of calculating accuracy of measuring the height of objects used decomposition of the function into a Taylor series. Currently, the standard deviation of measurement errors of height of flight of the aircraft, the basis of stereozone and focal length, usually known with enough high accuracy. The main influence on the accuracy of determining the heights of objects during automatic processing of images is the accuracy of parallax. When measuring parallax, the problem is reduced to the search and discovery of images of the object in the second picture on the image of the object on the first image and measuring its position over images of other objects and noise. Using the formula of Kramer-Rao for the potential measurement accuracy of the image coordinates of the object in the picture, the Fourier transform and the parseval equality proof the identity, the formula obtained accuracy potential of combining stereochemical (measurement of parallax). We used the extreme-correlation combination method, as it can be applied for virtually any signals and systems of measurement. Analysis of the obtained results. The analysis of the obtained formulas shows that the overlay accuracy of the images deteriorates with the increase of the power spectral density of the noise on the first and second images and reducing the similarity of one image with another and also with the decrease in the effective width of a mutual spectrum spatial stereo. Increasing the value of the basis stereozone error of measurement of heights of objects first improves and then deteriorates. This deterioration is caused by the fact that the images of a stereo pair are obtained from different spatial points and images arise of perspective distortion and the distortion due to relief. Accordingly, as the base of removal increases, these distortions will increase. Conclusions. The advantage of this approach is the use of finite analytical expression. It provides the ability to calculate the potential accuracy of defining object heights when building a DMR with modern applications. The disadvantages include the complexity of calculating the moments of mutual spatial spectrum of stereo images. This approach can be applied when planning the shooting mode and the Earth surface imaging equipment for mapping, 3D models, etc.

Evaluation of the n-alkane technique for estimating herbage dry matter intake of dairy cows offered herbage harvested at two different stages of growth in summer and autumn

The n-alkane technique for estimating herbage dry matter intake (DMI) of dairy cows was investigated in this experiment. Eight Holstein-Friesian dairy cows were offered perennial ryegrass ad libitum that had been harvested at two different herbage masses and during two different seasons, in order to assess the effect of herbage mass and season on the accuracy of the n-alkane technique. Two pre-harvested herbage mass treatments (low, target 1500 kg DM/ha versus high, target 4000 kg DM/ha, measured above 4 cm), were investigated in a crossover factorial arrangement within each of two seasons (summer versus autumn), in Ireland. Each season consisted of two periods, each 12 days in length. Cows were housed in individual metabolism stalls to allow for accurate determination of measured DMI. Herbage DMI was estimated, with the n-alkane technique, by dosing cows twice daily with a C32 n-alkane. Pre-harvest herbage mass and season did not affect the n-alkane estimated DMI, although lack of season and herbage mass effects may have been masked by variation that occurred between swards within the same herbage mass and season. However, there were a number of differences between summer and autumn in the fecal recovery rates of a number of n-alkanes suggesting that the effect of season requires further investigation prior to the application of recovery rates from literature values when investigating diet selection and botanical composition. Overall, the n-alkane technique provided good estimates of DMI; the discrepancy had a standard deviation due to sward of 1.2 and 1.0 kg DM/cow per day, and hence potential bias of up to twice this, and a measurement error standard deviation of 1.3 and 1.0 kg DM/cow per day, for the C33/C32 and C31/C32 n-alkane pair methods respectively. Two n-alkane pairs were tested, and C33/C32 n-alkane provided the most precise estimates of DMI, compared with the C31/C32 n-alkane pair. This research provides some strong evidence for future use of the n-alkane technique including that the accuracy of the technique has not been influenced by contemporary changes to herbage management, is not affected by seasonal changes, and overall is an accurate and precise technique for estimating DMI.

A Hall Sensor-Based Position Measurement With On-Line Model Parameters Computation for Permanent Magnet Synchronous Linear Motor

With the advantage of low cost and small size, a hall sensor has been exploited to detect motor position, and this strategy has attracted much attention. A challenge is that measurement model parameters vary with position and vary from motor to motor because of the machining errors of permanent magnets. While, most existing methods use other auxiliary displacement sensors to calibrate model parameters off-line, which require a lot of preliminary work and lose adaptation when they are applied in industry. In this paper, an on-line simultaneous computation of model parameters and position method is proposed to measure position for a permanent magnet synchronous linear motor. The measurement model with Fourier series is employed to approximate the mapping relationship between magnetic field strength and mover position. Based on the continuous variation characteristics of model parameters and position, a simultaneous computational algorithm is proposed to real-timely compute model parameters and position without other sensors. In the experiments of one-way and reciprocating motion, magnetic field information is detected by a self-designed hall sensor array. Experimental results indicate that the standard deviation of measurement error is less than $10~\mu \text{m}$ with the comparison of a reference optical encoder.

Altitude Estimation Using Multipath With a Two-Dimensional Radar Over Spherical Earth

This paper presents a target altitude estimation approach based on multipath detections with range and range rate information from a two-dimensional (2-D) airborne radar. Using multipath detections has to deal with the following challenges: first, low probability of detection (PD) of the indirect path signal reflected by the sea surface; second, lack of an analytical expression for the relationship between the target motion parameter/state and the indirect path measurements over spherical earth; and third, unknown range measurement error standard deviation (s.d.) for the indirect path signal. Two estimators are developed: an adaptive multiple model iterated least squares (AMM-ILS) estimator for motion parameter estimation (noiseless target motion) and an AMM unscented Kalman filter (AMM-UKF) for dynamic state estimation (noisy target motion). Altitude estimate accuracy is studied based on simulation data. It shows that the AMM-ILS yields statistically efficient estimates (i.e., optimal and with a quantifiable accuracy), but this is not always true for the AMM-UKF. For a long distant target (e.g., 300 km) with very low indirect path PD (0.1 and 0.2), the AMM-UKF is inconsistent and inefficient statistically, due to biased estimation. The altitude Cramer Rao lower bounds from a 3-D radar with range and elevation measurements are also computed for comparison. The results show that the 2-D radar can provide better altitude estimates than the 3-D radar in most of the cases, except when the 3-D radar has accurate elevation measurement (with error s.d. $\sigma _e=0.5^{\circ }$ ) and the 2-D radar has very low indirect path PD (PD = 0.1).

The effect of measurement errors on the adaptive EWMA chart

AbstractThe AEWMA chart is an Adaptive EWMA (Exponentially Weighted Moving Average)–type chart that combines the Shewhart and the classical EWMA schemes in a smooth way. Its performance has been studied under the assumption that there is no measurement error in the quality characteristic. In this paper, we investigate the performance of the AEWMA chart when measurement errors exist using a linearly covariate error model. The presence of measurement errors with a linearly increasing measurement error standard deviation is also investigated. It turns out that, with the existence of measurement errors, the efficiency of the AEWMA chart can be strongly affected, and the negative effect can be compensated by taking multiple measurements at each sample point. Comparisons with the classical EWMA scheme confirm the superiority of the AEWMA scheme in detecting a wide range of shifts even in the presence of measurement errors. An example is provided to illustrate the use of the AEWMA chart with measurement errors.

Reproducibility of the transvaginal sonographic assessment of bladder wall thickness

ObjectiveTo assess whether transvaginal sonographic measurements of bladder wall thickness (BWT) have adequate reproducibility to detect differences in BWT potentially indicative of detrusor overactivity in women with overactive bladder. Study designThree reproducibility studies were undertaken to assess (A) total measurement error, (B) intra-observer variability and (C) inter-observer measurement in the interpretation of scans. Women recruited to the Bladder Ultrasound Study underwent a transvaginal ultrasound scan to obtain a measurement of BWT. When a second observer was available, women who agreed to have two transvaginal scans by different operators were recruited into study A. For study B the first observer reassessed a sample of the recorded images at a later date whilst for study C, a random selection of BWT images were read by a second assessor. Analytical variability, percentage of variability attributable to measurement error, within-person variation and the smallest real difference detectable were estimated. ResultsOne hundred and twenty-one women took part: 27 had repeat scans, 37 had scans re-read by the same observer, and 57 had scans read by two observers. In study A, 39% of the total variability in measurements was explained by measurement error (the remainder to within person change); the standard deviation (SD) of measurement error was 0.76mm and the smallest detectable clinical difference was 2.1mm. The SD of measurement error from scan interpretation was 0.42mm within observers (study B) and 0.35mm between observers (studyC). ConclusionThe high levels of measurement error for a small measurement of BWT means it is unlikely Transvaginal ultrasound measurements have insufficient reliability and reproducibility to be an accurate diagnostic test.

Evaluation and calibration of mobile phones for noise monitoring application.

The increasing number and quality of sensors integrated in mobile phones have paved the way for sensing schemes driven by city dwellers. The sensing quality can drastically depend on the mobile phone, and appropriate calibration strategies are needed. This paper evaluates the quality of noise measurements acquired by a variety of Android phones. The Ambiciti application was developed so as to acquire a larger control over the acquisition process. Pink and narrowband noises were used to evaluate the phones' accuracy at levels ranging from background noise to 90 dB(A) inside the lab. Conclusions of this evaluation lead to the proposition of a calibration strategy that has been embedded in Ambiciti and applied to more than 50 devices during public events. A performance analysis addressed the range, accuracy, precision, and reproducibility of measurements. After identification and removal of a bias, the measurement error standard deviation is below 1.2 dB(A) within a wide range of noise levels [45 to 75 dB(A)], for 12 out of 15 phones calibrated in the lab. In the perspective of citizens-driven noise sensing, in situ experiments were carried out, while additional tests helped to produce recommendations regarding the sensing context (grip, orientation, moving speed, mitigation, frictions, wind).

Locating hazardous gas leaks in the atmosphere via modified genetic, MCMC and particle swarm optimization algorithms

Hazardous gas leaks in the atmosphere can cause significant economic losses in addition to environmental hazards, such as fires and explosions. A three-stage hazardous gas leak source localization method was developed that uses movable and stationary gas concentration sensors. The method calculates a preliminary source inversion with a modified genetic algorithm (MGA) and has the potential to crossover with eliminated individuals from the population, following the selection of the best candidate. The method then determines a search zone using Markov Chain Monte Carlo (MCMC) sampling, utilizing a partial evaluation strategy. The leak source is then accurately localized using a modified guaranteed convergence particle swarm optimization algorithm with several bad-performing individuals, following selection of the most successful individual with dynamic updates. The first two stages are based on data collected by motionless sensors, and the last stage is based on data from movable robots with sensors. The measurement error adaptability and the effect of the leak source location were analyzed. The test results showed that this three-stage localization process can localize a leak source within 1.0 m of the source for different leak source locations, with measurement error standard deviation smaller than 2.0.

Fundamental Limits of TOA/DOA and Inertial Measurement Unit-Based Wireless Capsule Endoscopy Hybrid Localization

In this paper, performance analysis of hybrid localization based on radio-frequency (RF) and inertial measurement unit (IMU) measurements for a single wireless capsule endoscopy (WCE) traveling the gastrointestinal tract is studied. Specifically, the multiple body-mounted sensors are considered which are located on the front and back of a patient’s medical jacket and form the uniform rectangular arrays (URAs). With the aim of locating the WCE, two types of RF measurements, namely time-of-arrival (TOA) and direction-of-arrival (DOA), are estimated from the received signals at the URAs transmitted by the WCE, which are integrated with the IMU acceleration measurements via the standard extended Kalman filter. Here, a posterior Cramer–Rao Bound (PCRB) of the proposed TOA/DOA and IMU-based hybrid localization is derived as fundamental limits on squared position error, where the accuracies of TOA and DOA measurements are entailed by means of CRB to account for their dependency on the environmental parameters, while the accuracies of the IMU measurements are addressed with the acceleration measurement error standard deviation. Numerical results are provided, sustained by simulations which verify the millimeter accuracy of the TOA/DOA and IMU-based hybrid localization within the regulation of medical implant communication services and the exactness of the PCRB.

Weak Tsunami Detection Using GNSS-R-Based Sea Surface Height Measurement

This paper investigates weak tsunami detection using noisy sea surface height (SSH) measurement data such as that recorded by a satellite-borne receiver and produced by the Global Navigation Satellite System (GNSS) reflectometry (GNSS-R) technique. By studying the patterns of many real tsunamis, a triangle function is proposed to model the shape of tsunami lead waves for theoretical studies. Very similar simulation results are produced when the modeled and real tsunami data are used separately, indicating good modeling accuracy. A bin averaging (BA) technique is proposed for detecting a tsunami, and a hypothesis testing method is developed to decide whether a tsunami is present by examining the BA outputs against a predefined threshold. Mathematical formulas are derived for the probability of detection (PD) and the probability of false alarm (PFA), which can be employed as a guideline in parameter selection and performance evaluation. Simulation results using both modeled and real tsunami data demonstrate that, given a PFA of 10%, the PD can be around 60% when the wave height is 45 cm, and the SSH measurement error standard deviation (STD) is 76 cm. The results also show that, when a suitable bin length is selected, a two-stage hypothesis testing scheme and a one stage one produce very similar results. Based on the methods developed here and elsewhere, the GNSS-R technique has the potential for future tsunami detection.

A Novel Three Coding-pitches Triangular Patterns Phase-shifting Profilometry based on Modified Sunzi Theorem

In order to realize the high precision real-time measurement for the static objects, three coding-pitches triangular patterns phase-shifting profilometry based on modified Sunzi Theorem (ST) was proposed in this paper. First, according to Sunzi Theorem, the triangular pattern is designed. This Sunzi Theorem was adopted to unwrap three wrapped coordinate acquired from triangular patterns fringe images. The greatest common divisor of codingpitches is obtained by the used projector. In unwrapping processing, the wrapped coordinate is considered as remainder of the absolute coordinate modulo of the coding-pitch. Generally there are two kinds of rounding policies for the remainder in real number set. If the rounding policy selection is wrong, the rounding result of remainder containing decimal fraction error which can lead the unwrapping result to quite away from the correct one. In order to solve the high sensitivity of the decimal fraction error, the decimal fraction difference is recognized as the criterion of the rounding policy selection for real number erroneous remainder. To verify the presented method in this paper, a 3D shape measurement experimental system is constructed using projector and camera. The experiment results shown that, a maximum standard deviation of measurement error to the rule 3D objects is 0.62mm, and the complex surface reconstruction with different surface reflectivity can be realized very well.

A randomized, observer-blind comparison between the Neurotip mounted Neuropen and a disposable plastic neurological wheel for assessing the level of spinal blockade at cesarean section

BackgroundVarious methods are used to assess the height of sensory block to touch under spinal anesthesia for cesarean section. We tested a novel, inexpensive, miniature, user-dependent plastic neurological wheel against the user-independent Neurotip mounted Neuropen. MethodsPatients received either spinal or combined spinal–epidural anesthesia. For each patient assessment, the devices were randomly assigned to one of two independent investigators. The order of device application was randomly permuted. Neither researcher was involved with anesthetic care. At 5-min intervals for 20min after spinal injection, and again at the end of the operation, the levels of block to loss-of-touch sensation were assessed. While one investigator evaluated the block, the other left the operating room and vice versa. Mixed-effects regression and Bland–Altman analysis were used to weigh agreement between devices. ResultsThe mean difference in level-to-touch was 0.04 (95% CI −0.18, 0.27) dermatome levels. Measurement error standard deviation associated with the Neurotip mounted Neuropen and plastic neurological wheel was 1.36 (95% CI 1.26, 1.41) and 1.33 (95% CI 1.26, 1.46) dermatome levels, respectively. The difference in measurement error standard deviation was −0.03 (95% CI −0.16, 0.24). This evidence excludes the possibility, with 95% confidence, of clinically significant bias or measurement error differences between methods. Occasional wide variances in dermatome level were observed with both instruments at the initial assessment only. ConclusionThe compact plastic neurological wheel is as clinically reliable as the Neurotip mounted Neuropen.

A comparison of least squares and conditional maximum likelihood estimators under volume endpoint censoring in tumor growth experiments

Measurements in tumor growth experiments are stopped once the tumor volume exceeds a preset threshold: a mechanism we term volume endpoint censoring. We argue that this type of censoring is informative. Further, least squares (LS) parameter estimates are shown to suffer a bias in a general parametric model for tumor growth with an independent and identically distributed measurement error, both theoretically and in simulation experiments. In a linear growth model, the magnitude of bias in the LS growth rate estimate increases with the growth rate and the standard deviation of measurement error. We propose a conditional maximum likelihood estimation procedure, which is shown both theoretically and in simulation experiments to yield approximately unbiased parameter estimates in linear and quadratic growth models. Both LS and maximum likelihood estimators have similar variance characteristics. In simulation studies, these properties appear to extend to the case of moderately dependent measurement error. The methodology is illustrated by application to a tumor growth study for an ovarian cancer cell line.

Robust location algorithm based on weighted least-squares support vector machine (WLS-SVM) for non-line-of-sight environments

One of the main problems facing accurate location in wireless communication systems is non-line-of-sight (NLOS) propagation. Though learning location methods perform well in NLOS environments, learning location methods may be improved further since these methods do not consider outliers in the training data set. In this paper, we extend weighted least squares support vector machine (WLS-SVM) algorithm to mobile location problem. The proposed method can effectively suppress outliers with different weights. In simulation, we analyze the effects of the number of training points, the percentage of outliers in training data set, the standard deviation and mean of outliers, and the standard deviation of measurement error. Simulation results show that the proposed algorithm clearly outperforms three other algorithms (LS method, kernel method and LS-SVM based method). Key words: Weighted least-squares support vector machine (WLS-SVM), non-line-of-sight (NLOS).