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PubMed1980

Mass spectrometry in anesthesia. Problems in using mass spectrometer for monitoring anesthetic gases and vapours.

The use of mass spectrometers for total gas monitoring during anesthesia presents a number of problems which stem from the Cracking Pattern of the gases present, inlet design, viscosity variations, water vapour and machine deterioration. Some of these have been adequately solved, by making mechanical modifications to the inlet system, and by using more complex electronic circuitry to process the signals obtained. Remaining problems, however, still limit accuracy and ease of operation. CO2 measurements are particularly prone to error, especially when sampling halothane-containing gas which leads to significant internal production CO2. A study of the principal sources of error remaining in the machine suggests that the only definitive solution is to develop a microprocessor system which could cope with complex Cracking Patterns and non-linearities, and which would allow complete automation of the calibration procedure.

Anesthetics↗
PubMed1984

Sampling schemes for estimating nerve fibre size. II. Methods for unifascicular nerve trunks.

The total number of myelinated fibres in four unifascicular tibial nerves from diabetic rats has been counted and measured in order to assess the merits of various schemes for estimating group mean fibre diameter. The average nerve trunk contained some 2960 fibres which were measured in just under five hours. With different sampling designs, the average measurement time per nerve was reduced to between 17 and 69 minutes, with little consequent loss of reliability or precision of estimated mean fibre size. The most efficient schemes were those taking systematic samples of squares or sectors. A modification of a method relying on complete strips across two diameters of each nerve was the least efficient sampling approach. It had the additional disadvantage of introducing systematic errors which could affect the accuracy of measurements made on nerve trunks with heterogeneous spatial distributions of fibre size and number. This paper completes an investigation into random sampling errors influencing morphometric estimates of fibre size based on uni- or multifascicular nerve trunks.

Animals↗
PubMed1997

Caffeine in saliva after peroral intake: early sample collection as a possible source of error.

The influence of collection time on the correlation of caffeine concentrations in saliva and serum was examined in six healthy adults after peroral administration of 5 mg/kg caffeine citrate. Saliva was obtained from three different salivary glands (sublingual, right parotid, and left parotid) and evaluated separately. Caffeine concentrations in saliva and serum samples were determined by high-performance liquid chromatography. There were no differences in the caffeine concentrations in saliva from the three investigated glands (alpha = 0.05). Saliva samples collected earlier than 2 hours after caffeine intake showed higher caffeine concentrations than could be expected from the corresponding serum samples. Gingiva contamination was shown to be responsible for the higher caffeine concentrations in saliva, and it was concluded that saliva is a feasible matrix for therapeutic drug monitoring of caffeine. If caffeine is administered orally, saliva samples should be taken at least 2 hours after caffeine intake. If caffeine-containing beverages are used as the source of caffeine or if subjects do not cooperate by rinsing the mouth of caffeine contamination, an additional 60 minutes should be added before saliva sampling.

Administration, Oral↗
PubMed1991

Turns-amplitude analysis at different sampling frequencies.

In the EMG interference pattern the number of potential reversals of more than 100 microV (i.e., turns) measured may be low if a low sampling frequency is used. This might be more pronounced in a myopathic muscle with small short potentials than in a control muscle, resulting in a decreased diagnostic yield. The influence of sampling frequencies from 6 to 200 kHz on the turns, mean amplitude and ratio of turns to mean amplitude analysed on the interference pattern at a force of 30% of maximum was examined at 10 sites in each of 5 control muscles, 5 myopathic muscles and 5 neurogenic muscles (i.e., 150 sites in all). In this small group of muscles low sampling frequency did not tend to reduce the diagnostic yield of the measurements. Proper reproducibility was obtained with sampling frequencies down to 17 kHz. However, due to systematic errors, measurements obtained with sampling frequencies below 25 kHz require comparable control values or compensations for errors. As time intervals between turns (not studied here) have a skew distribution with many small time intervals a sampling frequency of 50 kHz or higher is probably required.

Adult↗
PubMed1977

The effects of a finite number of projection angles and finite lateral sampling of projections on the propagation of statistical errors in transverse section reconstruction.

The dependence of noise amplification on the nuber of projection angles and on the lateral sampling interval of projections is presented. It is shown that about 1-5D/d angles and a sampling interval of about 0-5d are required in order that the data be efficiently utilized. D is the linear dimension of the reconstruction region and d is the linear dimension of the cells into which the reconstruction region is subdivided (resolution length). Values for noise amplification are given for various combinations of projection angles and lateral sampling intervals.

Information Theory↗
PubMed1995

The problem of the type II statistical error.

OBJECTIVE: To determine if type II statistical errors (also known as beta errors) are a common problem in published clinical research. METHODS: Type II statistical errors occur when sample sizes are too small to show an effect of treatment, even when an effect truly exists. Searching the Medline data base, we identified ten meta-analyses published during 1986-1994 in the American Journal of Obstetrics and Gynecology, Obstetrics and Gynecology, and The Journal of Reproductive Medicine. Meta-analyses were used as sources of component or individual studies for the following reason: When small component studies have negative findings that differ from the overall conclusions of the meta-analysis, the component studies may have type II statistical errors. RESULTS: We found that only 6.5% (15 of 231) of component studies provided any documentation that power calculations to determine sample sizes had been done a priori (before) the research began. Thus, many of these component studies with findings of no treatment effect may have had type II errors because of too-small sample sizes. When stratifying the component studies by year of publication, we found that 7.9% (14 of 178) of studies published in the 1980s and 1990s had any documented evidence of a priori power calculations. In the 1960s and 1970s, only one of 53 component studies had documented evidence of power calculations. CONCLUSION: To ensure that truly effective treatments are introduced into clinical practice as quickly as possible, we believe that a priori power calculations should always be done in quantitative clinical research.

Meta-Analysis as Topic↗
PubMed2003

Modelling a minimal residual disease-based treatment strategy in childhood acute lymphoblastic leukaemia.

The measurement of minimal residual disease (MRD) in childhood acute lymphoblastic leukaemia offers the promise of individualized, risk-stratified treatment, but an optimal protocol needs establishing. A model was developed to explore certain unanswered questions. The model assumes that all patients have MRD assessed after induction chemotherapy and children above a certain threshold are offered intensive chemotherapy. Using parameter estimates derived from published studies of MRD, the model predicted event-free survival (EFS) rates, relapse rates and treatment-related mortality for a cohort of children in the first presentation who were Philadelphia chromosome negative. Using the level of MRD after induction in order to decide on the use of intensive therapy resulted in an increase in EFS rates of up to 2.9 per 100 children, although if the error of the MRD measurement were too great, the benefit was almost nullified. Taking and analysing more than one marrow sample from the patient for the MRD measurement, in order to reduce sampling and measurement error, improved EFS by a further 1.1 patients per 100 treated, and decreased the number of patients offered intensive therapy by up to 2.6 per 100 treated. The optimal threshold for offering intensive therapy was in the range of 10-3.5- 10-4.5 cells if the intensive treatment-related mortality was 13-18% (allograft options), but 10-5- 10-6 cells if it was less than 8% (intensified chemotherapy). Using MRD to target patients at a high risk of relapse improved EFS rates, but the accuracy of measurements was of critical importance.

Antineoplastic Agents↗
PubMedDate not supplied

Sampling framework for accurate curvature estimation in discrete surfaces.

Accurate curvature estimation in discrete surfaces is an important problem with numerous applications. Curvature is an indicator of ridges and can be used in applications such as shape analysis and recognition, object segmentation, adaptive smoothing, anisotropic fairing of irregular meshes, and anisotropic texture mapping. In this paper, a new framework is proposed for accurate curvature estimation in discrete surfaces. The proposed framework is based on a local directional curve sampling of the surface where the sampling frequency can be controlled. This local model has a large number of degrees of freedoms compared with known techniques and, so, can better represent the local geometry. The proposed framework is quantitatively evaluated and compared with common techniques for surface curvature estimation. In order to perform an unbiased evaluation in which smoothing effects are factored out, we use a set of randomly generated Bezier surface patches for which the curvature values can be analytically computed. It is demonstrated that, through the establishment of sampling conditions, the error in estimations obtained by the proposed framework is smaller and that the proposed framework is less sensitive to low sampling density, sampling irregularities, and sampling noise.

Algorithms↗
PubMed1994

[A simple method for measurement of cerebral blood flow using 123I-IMP SPECT with calibrated standard input function by one point blood sampling; validation of calibration by one point venous blood sampling as a substitute for arterial blood sampling].

In a simplified method for measurement of cerebral blood flow using one 123I-IMP SPECT scan and one point arterial blood sampling (Autoradiography method), input function is obtained by calibrating a standard input function by one point arterial blood sampling. A purpose of this study is validation of calibration by one point venous blood sampling as a substitute for one point arterial blood sampling. After intravenous infusion of 123I-IMP, frequent arterial and venous blood sampling were simultaneously performed on 12 patients of CNS disease without any heart and lung disease and 5 normal volunteers. The radioactivity ratio of venous whole blood which obtained from cutaneous cubital vein to arterial whole blood were 0.76 +/- 0.08, 0.80 +/- 0.05, 0.81 +/- 0.06, 0.83 +/- 0.11 at 10, 20, 30, 50 min after 123I-IMP infusion, respectively. The venous blood radioactivities were always 20% lower than those of arterial blood radioactivity during 50 min. However, the ratio which obtained from cutaneous dorsal hand vein to artery were 0.93 +/- 0.02, 0.94 +/- 0.05, 0.98 +/- 0.04, 0.98 +/- 0.03, at 10, 20, 30, 50 min after 123I-IMP infusion, respectively. The venous blood radioactivity was consistent with artery. These indicate that arterio-venous difference of radioactivity in a peripheral cutaneous vein like a dorsal hand vein is minimal due to arteriovenous shunt in palm. Therefore, a substitution by blood sampling from cutaneous dorsal hand vein for artery will be possible. Optimized time for venous blood sampling evaluated by error analysis was 20 min after 123I-IMP infusion, which is 10 min later than that of arterial blood sampling.

Amphetamines↗
PubMed2006

Confidence-based active learning.

This paper proposes a new active learning approach, confidence-based active learning, for training a wide range of classifiers. This approach is based on identifying and annotating uncertain samples. The uncertainty value of each sample is measured by its conditional error. The approach takes advantage of current classifiers' probability preserving and ordering properties. It calibrates the output scores of classifiers to conditional error. Thus, it can estimate the uncertainty value for each input sample according to its output score from a classifier and select only samples with uncertainty value above a user-defined threshold. Even though we cannot guarantee the optimality of the proposed approach, we find it to provide good performance. Compared with existing methods, this approach is robust without additional computational effort. A new active learning method for support vector machines (SVMs) is implemented following this approach. A dynamic bin width allocation method is proposed to accurately estimate sample conditional error and this method adapts to the underlying probabilities. The effectiveness of the proposed approach is demonstrated using synthetic and real data sets and its performance is compared with the widely used least certain active learning method.

Algorithms↗
PubMed1979

Performance specifications for infrared milk analysis.

Maximum limits of 0.02% are recommended for precision of IR analysis for fat, protein, and lactose, and 0.04% for total solids. Recommended maximum systematic errors are 0.06% for fat, protein, and lactose, and 0.12% for total solids, when instrument results are compared with results of specified AOAC methods. Recommended maximum mean differences between instrument and standard results are based on 95% confidence limits for the mean of 8 samples; precision and systematic errors are calculated as the standard deviation of difference between duplicates for 8 samples, and systematic errors are calculated as the standard deviation of difference between instrument and reference results for 8 samples. Automated sections for milk of Official Methods of Analysis were rewritten to eliminate references to individual instruments, to eliminate possible differences between calibration procedures for different instruments, and to stress important instrument operational characteristics which can have significant effects on instrument performance.

Animals↗
PubMed2006

A permutation test for comparing ROC curves in multireader studies a multi-reader ROC, permutation test.

RATIONALE AND OBJECTIVES: The aim of the study is to develop a permutation test to compare receiver operating characteristic (ROC) curves of two diagnostic modalities in a multireader paired design. MATERIALS AND METHODS: A statistical test for comparing two diagnostic modalities is developed based on all possible exchanges of the set of reader-ratings between the two modalities. An exact permutation test is formed by determining the frequency of the most extreme values of the statistic estimating the average difference in the areas under the ROC curves (AUCs). An asymptotic version of the test is constructed by obtaining the exact permutation variance and appealing to the asymptotic normality of the nonparametric estimator of the average difference in areas. Computer simulations were conducted to validate the type I error for small sample sizes. RESULTS: The new test provides a permutation approach for comparing ROC curves in a multireader paired-design setting in which effects of the readers are considered to be fixed. The type I error of the asymptotic test is close to the true value, even for samples as small as 20 normal and 20 abnormal cases. The test is designed to be sensitive to alternatives in which the AUCs of the two diagnostic modalities differ. CONCLUSIONS: The proposed test provides a powerful method for comparing two diagnostic modalities in a multireader paired-study design when the primary interest is to detect difference in average AUCs.

Analysis of Variance↗
PubMed2002

Power and sample size calculations for case-control genetic association tests when errors are present: application to single nucleotide polymorphisms.

The purpose of this work is to quantify the effects that errors in genotyping have on power and the sample size necessary to maintain constant asymptotic Type I and Type II error rates (SSN) for case-control genetic association studies between a disease phenotype and a di-allelic marker locus, for example a single nucleotide polymorphism (SNP) locus. We consider the effects of three published models of genotyping errors on the chi-square test for independence in the 2 x 3 table. After specifying genotype frequencies for the marker locus conditional on disease status and error model in both a genetic model-based and a genetic model-free framework, we compute the asymptotic power to detect association through specification of the test's non-centrality parameter. This parameter determines the functional dependence of SSN on the genotyping error rates. Additionally, we study the dependence of SSN on linkage disequilibrium (LD), marker allele frequencies, and genotyping error rates for a dominant disease model. Increased genotyping error rate requires a larger SSN. Every 1% increase in sum of genotyping error rates requires that both case and control SSN be increased by 2-8%, with the extent of increase dependent upon the error model. For the dominant disease model, SSN is a nonlinear function of LD and genotyping error rate, with greater SSN for lower LD and higher genotyping error rate. The combination of lower LD and higher genotyping error rates requires a larger SSN than the sum of the SSN for the lower LD and for the higher genotyping error rate.

Case-Control Studies↗
PubMed1993

IOL power mislabelling.

Prompted by four cases of IOL power mislabelling, a method was developed which allowed the measurement of the IOL power using a keratometer. The principle of operation was to measure the curvature of the steepest surface of the IOL through a minus lens by which the size of the mires was brought into the measuring range of the keratometer. With this method the IOL power was checked in three random IOL samples from three companies. Although no large errors in IOL power labelling were encountered in these samples, the error of labelling was found to differ significantly between the companies. It was concluded, that poor manufacturing control of IOL power may add to the sources of error in IOL power prediction.

Aged↗
PubMed1988

Spectral analysis of inert gas elimination data: resolution limits.

A new method of analyzing inert gas data for recovery of the pulmonary ventilation-perfusion ration (VA/Q) distribution is proposed. It is shown that the conventional inert gas elimination equation takes the form of a convolution integral, and the relationship between VA/Q distribution and inert gas elimination resembles that of a noncausal low-pass filter with infinite zero-frequency gain. With the use of this formulation, characteristic features of VA/Q distribution may be represented in the frequency domain in terms of the corresponding energy spectrum. It is shown that the lack of resolution associated with finite data samples and measurement error is caused by distortions in the high-frequency contents of the resulting VA/Q distribution. With six inert gases, the technique cannot resolve a log SD less than 0.21 decade and a modal separation less than 0.87 decade. In the presence of measurement error, the degree of resolution is even less. It is suggested that for maximum resolution the number of discrete and duplicate data samples should be chosen so that the resulting noise and sampling cutoff frequencies are approximately equal.

Fourier Analysis↗
PubMed1998

Landmark identification error in submentovertex cephalometrics. A computerized method for determining the condylar long axis.

The purpose of this study was to examine the identification error of certain submentovertex landmarks and to compare three different methods of determining horizontal condylar angulation in submentovertex radiographs. To determine landmark identification error, a random sampling of 12 submentovertex radiographs from preorthodontic patients between the ages of 10 and 17 years was used to determine both intraexaminer and interexaminer reliability. The error associated with the identification of each of 11 landmarks varied between specific landmarks, between the same landmarks bilaterally, and between the vertical and horizontal components of the same landmark. In general, intraexaminer data showed less landmark identification error in both vertical and horizontal directions than did interexaminer data. The foramen spinosum landmarks demonstrated the lowest identification error in both horizontal and vertical direction (intraexaminer), whereas greater identification error was associated with the condylar lateral poles and posterior condylar points (both intraexaminer and interexaminer). A comparison of three different methods of condylar angulation determination was undertaken through the use of two tracings of each of 101 submentovertex radiographs. A computer-derived method representing the principal axis of minimum moment of inertia of the condyle was shown to be more reliable (p < 0.05) with respect to describing condylar angulation than both a method that used a best-fit line through the anterior condylar border and an interpolar axis method.

Adolescent↗
PubMed2003

Effect of metal and sampling rate on accuracy of Flock of Birds electromagnetic tracking system.

Electromagnetic tracking devices are used in many biomechanics applications. Previous studies have shown that metal located within the working field of direct current electromagnetic tracking devices produces significant errors. However, the effect of sampling rate on the errors produced in a metallic environment has never been studied. In this study, the accuracy of Ascension Technologies' Flock of Birds was evaluated at sampling rates of 20, 60, 100, and 140 Hz, in the presence of both aluminum and steel. Aluminum interference caused an increase in measurement error as the sampling rate increased. Conversely, steel interference caused a decrease in measurement error as the sampling rate increased. We concluded that the accuracy of the Flock of Birds tracking system can be optimized in the presence of metal by careful choice in sampling rate.

Electromagnetic Phenomena↗
PubMed2003

The validity of the Stanford Seven-Day Physical Activity Recall in young adults.

PURPOSE: To evaluate the criterion validity of the 7-Day Physical Activity Recall (7D-PAR) and factors associated with reporting error, in a sample of moderately overweight, young adult men and women. METHODS: Average total daily energy expenditure (TDEE) and physical activity energy expenditure (PAEE) from the 7D-PAR were compared with the same parameters assessed by doubly labeled water in 17 men, age = 23.9 +/- 3.8 yr, and 29 women, age = 23.3 +/- 4.6 yr, who volunteered to participate in a 16-month supervised aerobic exercise trial. PAEE was estimated from the 7D-PAR and from DLW [0.9 * TDEE -resting metabolic rate (RMR) (indirect calorimetry)]. In addition, peak oxygen uptake and percent body fat were obtained. RESULTS: No significant differences in TDEE (kJ.d-1) were noted between the 7D-PAR (11825 +/- 1779) and DLW (11922 +/- 2516) for the complete sample (N = 46) or for men (7D-PAR = 13198 +/- 1638, DLW = 13885 +/- 2754) or women (7D-PAR = 11018 +/- 1323, DLW = 10771 +/- 1457. The mean PAEE from the 7D-PAR was not different from DLW in the total sample (7D-PAR = 3286 +/- 502, DLW = 3508 +/- 1863) as well as in men (7D-PAR = 3650 +/- 490, DLW = 3989 +/- 2461) and women (3073 +/- 377, DLW = 3223 +/- 1360). In a regression model, PAEE, peak oxygen uptake, gender and percent fat accounted for 86% of the reporting error in total daily energy expenditure when using the 7D-PAR. CONCLUSION: The 7D-PAR provided a reasonable estimate of both the mean TDEE and PAEE in this sample; however, estimates of energy expenditure on an individual basis using the PAR were subject to considerable error.

Adolescent↗