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Validation Data (validation + data)
Terms modified by Validation Data Selected AbstractsDevelopment of an Index of Biotic Integrity for a Southeastern Coastal Plain Watershed, USA,JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION, Issue 2 2007Charles C. Morris Abstract:, This study evaluated biological integrity expectations of fish assemblages in wadeable streams for the Alabama portion of the Choctawhatchee River watershed using a multimetric approach. Thirty-four randomly selected stream sites were sampled in late spring 2001 to calibrate an index of biotic integrity (IBI). Validation data were collected during the spring 2001, and summer and fall of 2003 from disturbed and least-impacted targeted sites (n = 20). Thirty-five candidate metrics were evaluated for their responsiveness to environmental degradation. Twelve metrics were selected to evaluate wadeable streams and four replacement metrics were selected for headwater streams. Scores that ranged from 58 to 60 were considered to be representative of excellent biotic integrity (none found in this study), scores of 48-52 as good integrity (31% of the sites in this study), 40-44 as fair (43%), 28-34 as poor (21%), and 12-22 as very poor (5%). Of the four stream condition categories (urban, cattle, row crop, and least impacted), the IBI scores for urban and cattle sites differed significantly from least-impacted sites. Row crop sites, although not significantly different from least-impacted, tended to have greater variability than the other categories. Lower IBI scores at both urban and cattle sites suggest that the IBI accurately reflects stream impairment in the Choctawhatchee River drainage. [source] Simultaneous determination of honokiol and magnolol in Magnolia officinalis by liquid chromatography with tandem mass spectrometric detectionBIOMEDICAL CHROMATOGRAPHY, Issue 10 2006Yu-Tse Wu Abstract An optimized high-performance liquid chromatographic method coupled with tandem mass spectrometric detection (LC-MS/MS) was developed for the simultaneous determination of honokiol and magnolol in Magnolia officinalis. Honokiol and magnolol were separated from the extracts using a reversed-phase C18 column with a mobile phase consisted of acetonitrile and water (75:25, v/v) at a flow-rate of 0.8 mL/min. Selected reaction monitoring (SRM) mode was used for all sample quantification by the precursor-ion/product ion pair m/z 265 , m/z 224 for honokiol and m/z 265 , m/z 247 for magnolol. Validation data showed that this method has good linearity (r2 > 0.995) over the concentration range of 0.0025,0.5 µg/mL for honokiol and magnolol, and both intra- and inter-day variability were acceptable within 15% at the lowest concentrations for this method. This proposed method provides excellent specificity, higher sensitivity and shorter run time than conventional methods and was applied successfully to determine the contents of honokiol and magnolol in M. officinalis. Copyright © 2006 John Wiley & Sons, Ltd. [source] Selecting discriminant function models for predicting the expected richness of aquatic macroinvertebratesFRESHWATER BIOLOGY, Issue 2 2006JOHN VAN SICKLE Summary 1. The predictive modelling approach to bioassessment estimates the macroinvertebrate assemblage expected at a stream site if it were in a minimally disturbed reference condition. The difference between expected and observed assemblages then measures the departure of the site from reference condition. 2. Most predictive models employ site classification, followed by discriminant function (DF) modelling, to predict the expected assemblage from a suite of environmental variables. Stepwise DF analysis is normally used to choose a single subset of DF predictor variables with a high accuracy for classifying sites. An alternative is to screen all possible combinations of predictor variables, in order to identify several ,best' subsets that yield good overall performance of the predictive model. 3. We applied best-subsets DF analysis to assemblage and environmental data from 199 reference sites in Oregon, U.S.A. Two sets of 66 best DF models containing between one and 14 predictor variables (that is, having model orders from one to 14) were developed, for five-group and 11-group site classifications. 4. Resubstitution classification accuracy of the DF models increased consistently with model order, but cross-validated classification accuracy did not improve beyond seventh or eighth-order models, suggesting that the larger models were overfitted. 5. Overall predictive model performance at model training sites, measured by the root-mean-squared error of the observed/expected species richness ratio, also improved steadily with DF model order. But high-order DF models usually performed poorly at an independent set of validation sites, another sign of model overfitting. 6. Models selected by stepwise DF analysis showed evidence of overfitting and were outperformed by several of the best-subsets models. 7. The group separation strength of a DF model, as measured by Wilks',, was more strongly correlated with overall predictive model performance at training sites than was DF classification accuracy. 8. Our results suggest improved strategies for developing reliable, parsimonious predictive models. We emphasise the value of independent validation data for obtaining a realistic picture of model performance. We also recommend assessing not just one or two, but several, candidate models based on their overall performance as well as the performance of their DF component. 9. We provide links to our free software for stepwise and best-subsets DF analysis. [source] Simulating pan-Arctic runoff with a macro-scale terrestrial water balance modelHYDROLOGICAL PROCESSES, Issue 13 2003Michael A. Rawlins Abstract A terrestrial hydrological model, developed to simulate the high-latitude water cycle, is described, along with comparisons with observed data across the pan-Arctic drainage basin. Gridded fields of plant rooting depth, soil characteristics (texture, organic content), vegetation, and daily time series of precipitation and air temperature provide the primary inputs used to derive simulated runoff at a grid resolution of 25 km across the pan-Arctic. The pan-Arctic water balance model (P/WBM) includes a simple scheme for simulating daily changes in soil frozen and liquid water amounts, with the thaw,freeze model (TFM) driven by air temperature, modelled soil moisture content, and physiographic data. Climate time series (precipitation and air temperature) are from the National Centers for Environmental Prediction (NCEP) reanalysis project for the period 1980,2001. P/WBM-generated maximum summer active-layer thickness estimates differ from a set of observed data by an average of 12 cm at 27 sites in Alaska, with many of the differences within the variability (1,) seen in field samples. Simulated long-term annual runoffs are in the range 100 to 400 mm year,1. The highest runoffs are found across northeastern Canada, southern Alaska, and Norway, and lower estimates are noted along the highest latitudes of the terrestrial Arctic in North America and Asia. Good agreement exists between simulated and observed long-term seasonal (winter, spring, summer,fall) runoff to the ten Arctic sea basins (r = 0·84). Model water budgets are most sensitive to changes in precipitation and air temperature, whereas less affect is noted when other model parameters are altered. Increasing daily precipitation by 25% amplifies annual runoff by 50 to 80% for the largest Arctic drainage basins. Ignoring soil ice by eliminating the TFM sub-model leads to runoffs that are 7 to 27% lower than the control run. The results of these model sensitivity experiments, along with other uncertainties in both observed validation data and model inputs, emphasize the need to develop improved spatial data sets of key geophysical quantities (particularly climate time series) to estimate terrestrial Arctic hydrological budgets better. Copyright © 2003 John Wiley & Sons, Ltd. [source] Instabilities during batch sedimentation in geometries containing obstacles: A numerical and experimental study,INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 8 2007Rekha R. Rao Abstract Batch sedimentation of non-colloidal particle suspensions is studied with nuclear magnetic resonance flow visualization and continuum-level numerical modelling of particle migration. The experimental method gives particle volume fraction as a function of time and position, which then provides validation data for the numerical model. A finite element method is used to discretize the equations of motion, including an evolution equation for the particle volume fraction and a generalized Newtonian viscosity dependent on local particle concentration. The diffusive-flux equation is based on the Phillips model (Phys. Fluids A 1992; 4:30,40) and includes sedimentation terms described by Zhang and Acrivos (Int. J. Multiphase Flow 1994; 20:579,591). The model and experiments are utilized in three distinct geometries with particles that are heavier and lighter than the suspending fluid, depending on the experiment: (1) sedimentation in a cylinder with a contraction; (2) particle flotation in a horizontal cylinder with a horizontal rod; and (3) flotation around a rectangular inclusion. Secondary flows appear in both the experiments and the simulations when a region of higher density fluid is above a lower density fluid. The secondary flows result in particle inhomogeneities, Rayleigh,Taylor-like instabilities, and remixing, though the effect in the simulations is more pronounced than in the experiments. Published in 2007 by John Wiley & Sons, Ltd. [source] Validation of ECMWF (re)analysis surface climate data, 1979,1998, for Greenland and implications for mass balance modelling of the ice sheetINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 2 2001Edward Hanna Abstract Climate (re)analysis products are potentially valuable tools, when properly verified, for helping to constrain the surface mass balance of the Greenland Ice Sheet (GIS). Monthly surface fields from European Centre for Medium-Range Weather Forecasts (ECMWF) operational- and re-analyses spanning 1979,1998 were validated using in situ data (surface air pressure and temperature, precipitation, cloud cover, short-/all-wave radiation, and wind speed/direction). These validation data are from coastal or near-coastal Danish Meteorological Institute (DMI) synoptic stations, inland Greenland Climate Network (GC-Net) and University of Wisconsin Automatic Weather Stations (AWSs), and two energy balance stations near the southern ice margin. The ECMWF analyses closely reproduce the seasonal patterns and interannual variations of much of the in situ data. Differences in the mean values of surface air pressure and temperature can mainly be ascribed to orography errors in the analyses' schemes, compared with the latest available accurate digital elevation model. Much of the GIS margin as modelled by ECMWF was too cold, on average by 4°C, and ECMWF precipitation averaged some 136% of the DMI station values. The misrepresentation of the (relatively) steep ice-sheet margin, which tends to be broadened and systematically over-elevated by several hundred metres, orographically reduced temperature and enhanced precipitation there in the ECMWF models. The cloud-cover comparison revealed not dissimilar annual mean cloud covers (ECMWF ,8%) but the ECMWF analyses had too little cloud and were too ,sunny' during the critical summer melt-season. ECMWF-modelled surface albedo in summer was ,11% lower than GC-Net values, which was mainly responsible for the disagreement of modelled surface short-wave radiation fluxes with observations. Model albedo and cloud errors need to be rectified if the analyses are to be used effectively to drive energy balance models of Greenland snowmelt. ECMWF wind speed averaged 66% (62%) of the DMI station (AWS) values. The validation results provide useful insights into how one can best improve the ECMWF Greenland climate data for use in glaciological and climatological studies. Copyright © 2001 Royal Meteorological Society [source] A unified approach to regression analysis under double-sampling designsJOURNAL OF THE ROYAL STATISTICAL SOCIETY: SERIES B (STATISTICAL METHODOLOGY), Issue 3 2000Yi-Hau Chen We propose a unified approach to the estimation of regression parameters under double-sampling designs, in which a primary sample consisting of data on the rough or proxy measures for the response and/or explanatory variables as well as a validation subsample consisting of data on the exact measurements are available. We assume that the validation sample is a simple random subsample from the primary sample. Our proposal utilizes a specific parametric model to extract the partial information contained in the primary sample. The resulting estimator is consistent even if such a model is misspecified, and it achieves higher asymptotic efficiency than the estimator based only on the validation data. Specific cases are discussed to illustrate the application of the estimator proposed. [source] 13C-methacetin breath test as a quantitative liver function test in patients with chronic hepatitis C infection: continuous automatic molecular correlation spectroscopy compared to isotopic ratio mass spectrometryALIMENTARY PHARMACOLOGY & THERAPEUTICS, Issue 2 2007O. GOETZE Summary Background The 13C-methacetin breath test (MBT) has been proposed for the non-invasive evaluation of hepatic microsomal activity. Aim To test a new continuous breath analysis system (BreathID) in comparison with gold-standard isotopic ratio mass spectrometry (IRMS) in patients with chronic hepatitis C infection and to assess the diagnostic performance of these validation data compared with liver biopsy for the quantification of liver fibrosis. Methods Fifty patients at different METAVIR stages received 75 mg of 13C-methacetin. Breath isotopic ratio was analysed over 90 min by BreathID (one sample/3 min; BreathID) and IRMS (one sample/10 min). Results were expressed as delta over baseline [DOB (%)] at each time interval and maximal DOB [DOBmax(%)]. Results A high linear association between both methods was observed (R2 = 0.95, P < 0.001). For all DOB and DOBmax, the limits of agreement by Bland,Altman analysis were within the predefined maximal width of s.d. <2.5%. MBT parameters in patients with high-grade fibrosis were different from patients with low-grade fibrosis (P < 0.001). Conclusion The MBT obtained by an easy to operate, automated BreathID provides results comparable with standard IRMS and differentiates fibrosis grades in patients with chronic hepatitis C infection. [source] Fatigue rating scales critique and recommendations by the Movement Disorders Society task force on rating scales for Parkinson's disease,MOVEMENT DISORDERS, Issue 7 2010Joseph H. Friedman MD Abstract Fatigue has been shown to be a consistent and common problem in Parkinson's disease (PD) in multiple countries and cultures. It is one of the most disabling of all symptoms, including motor dysfunction, and appears early, often predating the onset of motor symptoms. Several studies of the epidemiology of fatigue have been published, often using different scales, but few on treatment. The Movement Disorder Society (MDS) commissioned a task force to assess available clinical rating scales, critique their psychometric properties, summarize their clinical properties, and evaluate the evidence in support of their use in clinical studies in PD. Six clinical researchers reviewed all studies published in peer reviewed journals of fatigue in PD, evaluated the scales' previous use, performance parameters, and quality of validation data, if available. Scales were rated according to criteria provided by the MDS. A scale was "recommended" if it has been used in clinical studies beyond the group that developed it, has been used in PD and psychometric studies have established that it is a valid, reliable and sensitive to change in people with PD. Requiring a scale to have demonstrated sensitivity to change in PD specifically rather than in other areas in order to attain a rating of "recommended" differs from the use of this term in previous MDS task force scale reviews. "Suggested" scales failed to meet all the criteria of a "recommended" scale, usually the criterion of sensitivity to change in a study of PD. Scales were "listed" if they had been used in PD studies but had little or no psychometric data to assess. Some scales could be used both to screen for fatigue as well as to assess fatigue severity, but some were only used to assess severity. The Fatigue Severity Scale was "recommended" for both screening and severity rating. The Fatigue Assessment Inventory, an expanded version of the Fatigue severity Scale, is "suggested" for both screening and severity. The Functional Assessment of Chronic Illness Therapy-Fatigue was "recommended" for screening and "suggested" for severity. The Multidimensional Fatigue Inventory was "suggested" for screening and "recommended" for severity. The Parkinson Fatigue Scale was "recommended" for screening and "suggested" for severity rating. The Fatigue Severity Inventory was "listed" for both screening and severity. The Fatigue Impact Scale for Daily Use, an adaptation of the Fatigue Impact Scale was "listed" for screening and "suggested" for severity. Visual Analogue and Global Impression Scales are both "listed" for screening and severity. The committee concluded that current scales are adequate for fatigue studies in PD but that studies on sensitivity and specificity of the scales are still needed. © 2010 Movement Disorder Society [source] Dysautonomia rating scales in Parkinson's disease: Sialorrhea, dysphagia, and constipation,Critique and recommendations by movement disorders task force on rating scales for Parkinson's disease,MOVEMENT DISORDERS, Issue 5 2009Marian L. Evatt MD Abstract Upper and lower gastrointestinal dysautonomia symptoms (GIDS),sialorrhea, dysphagia, and constipation are common in Parkinson's disease (PD) and often socially as well as physically disabling for patients. Available invasive quantitative measures for assessing these symptoms and their response to therapy are time-consuming, require specialized equipment, can cause patient discomfort and present patients with risk. The Movement Disorders Society commissioned a task force to assess available clinical rating scales, critique their clinimetric properties, and make recommendations regarding their clinical utility. Six clinical researchers and a biostatistician systematically searched the literature for scales of sialorrhea, dysphagia, and constipation, evaluated the scales' previous use, performance parameters, and quality of validation data (if available). A scale was designated "Recommended" if the scale was used in clinical studies beyond the group that developed it, has been specifically used in PD reports, and clinimetric studies have established that it is a valid, reliable, and sensitive. "Suggested" scales met at least part of the above criteria, but fell short of meeting all. Based on the systematic review, scales for individual symptoms of sialorrhea, dysphagia, and constipation were identified along with three global scales that include these symptoms in the context of assessing dysautonomia or nonmotor symptoms. Three sialorrhea scales met criteria for Suggested: Drooling Severity and Frequency Scale (DSFS), Drooling Rating Scale, and Sialorrhea Clinical Scale for PD (SCS-PD). Two dysphagia scales, the Swallowing Disturbance Questionnaire (SDQ) and Dysphagia-Specific Quality of Life (SWAL-QOL), met criteria for Suggested. Although Rome III constipation module is widely accepted in the gastroenterology community, and the earlier version from the Rome II criteria has been used in a single study of PD patients, neither met criteria for Suggested or Recommended. Among the global scales, the Scales for Outcomes in PD-Autonomic (SCOPA-AUT) and Nonmotor Symptoms Questionnaire for PD (NMSQuest) both met criteria for Recommended, and the Nonmotor Symptoms Scale (NMSS) met criteria for Suggested; however, none specifically focuses on the target gastrointestinal symptoms (sialorrhea, dysphagia, and constipation) of this report. A very small number of rating scales have been applied to studies of gastrointestinal-related dysautonomia in PD. Only two scales met "Recommended" criteria and neither focuses specifically on the symptoms of sialorrhea, dysphagia, and constipation. Further scale testing in PD among the scales that focus on these symptoms is warranted, and no new scales are needed until the available scales are fully tested clinimetrically. © 2009 Movement Disorder Society [source] The Human Protein Atlas,a tool for pathology,THE JOURNAL OF PATHOLOGY, Issue 4 2008F Pontén Abstract Tissue-based diagnostics and research is incessantly evolving with the development of new molecular tools. It has long been realized that immunohistochemistry can add an important new level of information on top of morphology and that protein expression patterns in a cancer may yield crucial diagnostic and prognostic information. We have generated an immunohistochemistry-based map of protein expression profiles in normal tissues, cancer and cell lines. For each antibody, altogether 708 spots of tissues and cells are analysed and the resulting images and data are presented as freely available in the Human Protein Atlas (www.proteinatlas.org). The new version 4 of the atlas, including more than 5 million images of immunohistochemically stained tissues and cells, is based on 6122 antibodies, representing 5011 human proteins encoded by approximately 25% of the human genome. The gene-centric database includes a putative classification of proteins in various protein classes, both functional classes, such as kinases or transcription factors and project-related classes, such as candidate genes for cancer or cardiovascular diseases. For each of the internally generated antibodies, the exact antigen sequence is presented, together with a visualization of application-specific validation data, including a protein array assay, western blot analysis, immunohistochemistry and, in most cases, immunofluorescent-based confocal microscopy. The updated version also includes new search algorithms to allow complex queries regarding expression profiles, protein classes and chromosome location. Thus, the presented Human Protein Atlas provides a resource for pathology-based biomedical research, including protein science and biomarker discovery. Copyright © 2008 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd. [source] On the modelling of over-ocean hurricane surface winds and their uncertaintyTHE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 642 2009Dr. S. P. Khare Abstract This paper investigates the modelling of over-ocean hurricane surface wind fields and their associated uncertainty. The wind models tested include parameterized balance models, a two-dimensional numerical planetary boundary-layer model and a three-dimensional (3D) linear analytical boundary-layer model. Using a set of archived over-ocean surface wind field reconstructions for validation, a series of cross-validation experiments has been performed for a range of norms. For norms that quantify predictability of vector fields, a particular configuration of the 3D analytical model was found to be superior to the other models tested. Using residual fields derived from fitting the wind models to the validation data, the issue of how to model the uncertainty (in the form of a covariance) in the speed field has also been examined. Covariance models based on truncated empirical orthogonal function representations were found to be optimal. Copyright © 2009 Royal Meteorological Society [source] Analysis of Case-Only Studies Accounting for Genotyping ErrorANNALS OF HUMAN GENETICS, Issue 2 2007K. F. Cheng Summary The case-only design provides one approach to assess possible interactions between genetic and environmental factors. It has been shown that if these factors are conditionally independent, then a case-only analysis is not only valid but also very efficient. However, a drawback of the case-only approach is that its conclusions may be biased by genotyping errors. In this paper, our main aim is to propose a method for analysis of case-only studies when these errors occur. We show that the bias can be adjusted through the use of internal validation data, which are obtained by genotyping some sampled individuals twice. Our analysis is based on a simple and yet highly efficient conditional likelihood approach. Simulation studies considered in this paper confirm that the new method has acceptable performance under genotyping errors. [source] Differential impacts of habitat heterogeneity on male and female connectivity in a spatially structured pest systemAUSTRAL ECOLOGY, Issue 1 2009G. S. HAMILTON Abstract In a previous study, a model of landscape heterogeneity was developed and applied to a spatially structured wild rabbit (Oryctolagus cuniculus) population. That study showed clearly the influence of resource heterogeneity on connectivity levels. The simulation study was based on female movements and used population genetic validation data appropriate for a female study. Most models assume that males and females will exhibit similar patterns, although this has rarely been tested. In the current study we extend the analysis to consider differences between female and male connectivity in the same spatially structured pest system. Amplified fragment length polymorphism (AFLP) markers were screened on the same samples used previously for mtDNA analysis. The mtDNA data were used to validate female results, and AFLP data were used to validate combined male and female results. Connectivity patterns from the two simulations (female, and combined male and female) connectivity patterns showed no association. However, each was concordant with appropriate validation data, showing highly significant associations between pairwise population connectivity and the genetic data. A relative connectivity metric for the combined simulation was regressed against the mean of pairwise ,ST values, with almost 70% of the variation explained by a linear model. Demonstrating differential effects of habitat heterogeneity on male and female connectivity provides further evidence that spatial resource heterogeneity impacts on connectivity. Understanding differences in population connectivity will allow improved predictions of disease spread, local extinctions and recolonizations. Furthermore, modelling such differences in pest systems will allow management plans to be better targeted, for example by strategically introducing diseases for control purposes into populations which exhibit high male connectivity to aid spread, but low female connectivity to inhibit recolonization potential after control. [source] Ecological niche conservatism in North American freshwater fishesBIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 2 2009KRISTINA M. MCNYSET There are many hypotheses of relationships, and also of speciation processes, in North American freshwater fishes, although, to date, there have been no direct tests of whether there is evidence of ecological niche conservatism. In the present study, ecological niche modeling is used to look for evidence of ecological niche conservatism in six clades of freshwater fishes: the starheaded topminnows, sand darters, black basses, Notropis rubellus species group, Notropis longirostris species group, and the Hybopsis amblops species group. This is achieved by evaluating the reciprocal predictivity of distributional predictions based on ecological niche models developed for each individual taxon in a clade under the assumption that high reciprical predictivity between sister species can be taken as evidence of niche conservatism. Omission percentages, total and average commission, and the area under the curve in a receiver operating characteristic analysis, where calculated, are used to evaluate predictive ability. Occurrence data for each species were subset into a training and independent validation data set where possible. Across all clades and species, models predicted the validation data for a given species well. Ecological niche conservatism was found generally across the starheaded topminnows, the sand darters, and the N. longirostris species group. There was some inter-predictivity within the N. rubellus group, but almost no inter-predictivity within the black basses, indicating a lack of conservatism. These results demonstrate that ecological niches generally act as stable constraints on freshwater fish distributions in North America. © 2009 The Linnean Society of London, Biological Journal of the Linnean Society, 2009, 96, 282,295. [source] An analytical method for cyclosporine using liquid chromatography,mass spectrometryBIOMEDICAL CHROMATOGRAPHY, Issue 2 2010Srividya V. Kanduru Abstract A liquid chromatographic mass spectrometric (LC-MS) assay has been developed for cyclosporine A (CyA) in rat plasma using amiodarone as internal standard (IS). Rat plasma (100,µL) containing drug and IS were extracted using liquid,liquid extraction with 4,mL of 95:5 ether:methanol. After evaporation of the organic layer the residue was reconstituted with 500,µL of water. Then the aqueous layer was transferred to LC-MS sample vials. A 10,µL volume was injected. The analysis was performed on a C8 column 3.5,µm (2.1 × 50,mm) heated to 60°C with a mobile phase consisting of acetonitrile:methanol:0.2% NH4OH (60:20:20) at an isocratic flow-rate of 0.2,mL/min. The ions used for quantitation of CyA and IS were m/z 1202.8 and 645.9, with retention times of 3.35 and 4.72,min, respectively. Linear relationships (r2,>,0.99) were achieved between plasma or blood concentration and peak height ratios (drug:IS) over the concentration range 50,5000,ng/mL. The CV% and mean error were <19%. Based on validation data, the lower limit of quantification for the assay was 50,ng/mL. The reported assay method displayed high measures of linearity, sensitivity, reliability and precision, allowing its applicability in pharmacokinetic studies in rat. Copyright © 2009 John Wiley & Sons, Ltd. [source] Fluorescence determination of N -acetylaspartic acid in the rat cerebrum homogenate using high-performance liquid chromatography with pre-column fluorescence derivatizationBIOMEDICAL CHROMATOGRAPHY, Issue 1 2008Takeshi Fukushima Abstract N -Acetyl- l -aspartic acid (NAA) is an endogenous compound, and its brain concentration is suggested to be altered in neurological disorders. In the present study, a fluorescence determination method for NAA was developed by employing reversed-phase high-performance liquid chromatography (HPLC) with pre-column fluorescence derivatization using 4- N,N -dimethylaminosulfonyl-7- N -(2-aminoethyl)amino-2,1,3-benzoxadiazole (DBD-ED). Using methylsuccinic acid as the internal standard, a linear calibration curve for NAA was constructed in the range 125,1000 µm (n = 3). The detection limit on the column was approximately 5.0 fmol (signal-to-noise ratio 3). The proposed HPLC method was applied to determine NAA in the rat cerebrum homogenate. Cerebrum NAA was successfully determined using 10 µL of the homogenate, and the validation data for the proposed HPLC method demonstrated satisfactory results. Intra- and inter-day precision and accuracy were within 1.1,7.0 and ,8.1,6.3%, respectively. The concentration of NAA in the male rat cerebrum (13 weeks old) was 84 ± 4.6 µmol/mg protein (n = 3). Copyright © 2007 John Wiley & Sons, Ltd. [source] Regression Calibration in Semiparametric Accelerated Failure Time ModelsBIOMETRICS, Issue 2 2010Menggang Yu Summary In large cohort studies, it often happens that some covariates are expensive to measure and hence only measured on a validation set. On the other hand, relatively cheap but error-prone measurements of the covariates are available for all subjects. Regression calibration (RC) estimation method (Prentice, 1982,,Biometrika,69, 331,342) is a popular method for analyzing such data and has been applied to the Cox model by Wang et al. (1997,,Biometrics,53, 131,145) under normal measurement error and rare disease assumptions. In this article, we consider the RC estimation method for the semiparametric accelerated failure time model with covariates subject to measurement error. Asymptotic properties of the proposed method are investigated under a two-phase sampling scheme for validation data that are selected via stratified random sampling, resulting in neither independent nor identically distributed observations. We show that the estimates converge to some well-defined parameters. In particular, unbiased estimation is feasible under additive normal measurement error models for normal covariates and under Berkson error models. The proposed method performs well in finite-sample simulation studies. We also apply the proposed method to a depression mortality study. [source] Modeling Human Fertility in the Presence of Measurement ErrorBIOMETRICS, Issue 1 2000David B. Dunson Summary. The probability of conception in a given menstrual cycle is closely related to the timing of intercourse relative to ovulation. Although commonly used markers of time of ovulation are known to be error prone, most fertility models assume the day of ovulation is measured without error. We develop a mixture model that allows the day to be misspecified. We assume that the measurement errors are i.i.d. across menstrual cycles. Heterogeneity among couples in the per cycle likelihood of conception is accounted for using a beta mixture model. Bayesian estimation is straightforward using Markov chain Monte Carlo techniques. The methods are applied to a prospective study of couples at risk of pregnancy. In the absence of validation data or multiple independent markers of ovulation, the identifiability of the measurement error distribution depends on the assumed model. Thus, the results of studies relating the timing of intercourse to the probability of conception should be interpreted cautiously. [source] | ||||||||||||||||||||||