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Selection Procedures (selection + procedure)
Kinds of Selection Procedures Selected AbstractsReasons for Being Selective When Choosing Personnel Selection ProceduresINTERNATIONAL JOURNAL OF SELECTION AND ASSESSMENT, Issue 1 2010Cornelius J. König The scientist,practitioner gap in personnel selection is large. Thus, it is important to gain a better understanding of the reasons that make organizations use or not use certain selection procedures. Based on institutional theory, we predicted that six variables should determine the use of selection procedures: the procedures' diffusion in the field, legal problems associated with the procedures, applicant reactions to the procedures, their usefulness for organizational self-promotion, their predictive validity, and the costs involved. To test these predictions, 506 HR professionals from the German-speaking part of Switzerland filled out an online survey on the selection procedures used in their organizations. Respondents also evaluated five procedures (semi-structured interviews, ability tests, personality tests, assessment centers, and graphology) on the six predictor variables. Multilevel logistic regression was used to analyze the data. The results revealed that the highest odd ratios belonged to the factors applicant reactions, costs, and diffusion. Lower (but significant) odds ratios belonged to the factors predictive validity, organizational self-promotion, and perceived legality. [source] Candidates' Ability to Identify Criteria in Nontransparent Selection Procedures: Evidence from an assessment center and a structured interviewINTERNATIONAL JOURNAL OF SELECTION AND ASSESSMENT, Issue 3 2007Cornelius J. König In selection procedures like assessment centers (ACs) and structured interviews, candidates are often not informed about the targeted criteria. Previous studies have shown that candidates' ability to identify these criteria (ATIC) is related to their performance in the respective selection procedure. However, past research has studied ATIC in only one selection procedure at a time, even though it has been assumed that ATIC is consistent across situations, which is a prerequisite for ATIC to contribute to selection procedures' criterion-related validity. In this study, 95 candidates participated in an AC and a structured interview. ATIC scores showed cross-situational consistency across the two procedures and accounted for part of the relationship between performance in the selection procedures. Furthermore, ATIC scores in one procedure predicted performance in the other procedure even after controlling for cognitive ability. Implications and directions for future research are discussed. [source] An Agenda for Future Research on Applicant Reactions to Selection Procedures: A Construct-Oriented ApproachINTERNATIONAL JOURNAL OF SELECTION AND ASSESSMENT, Issue 1-2 2004David Chan This article offers an agenda for future research on applicant reactions to selection procedures. Advocating a construct-oriented approach, we propose that future research focuses attention on fundamental issues subsumed under seven distinct although related areas namely: (1) dimensions of applicant reactions, (2) changes in applicant reactions over time, (3) determinants of applicant reactions, (4) applicant reactions and test constructs, (5) criterion outcomes of applicant reactions, (6) reactions to new technology in testing, and (7) methodological and data analysis issues. [source] Applicant Reactions to Selection Procedures: An Updated Model and Meta-AnalysisPERSONNEL PSYCHOLOGY, Issue 3 2004John P. Hausknecht An updated theoretical model of applicant reactions to selection procedures is proposed and tested using meta-analysis. Results from 86 independent samples (N= 48,750) indicated that applicants who hold positive perceptions about selection are more likely to view the organization favorably and report stronger intentions to accept job offers and recommend the employer to others. Applicant perceptions were positively correlated with actual and perceived performance on selection tools and with self-perceptions. The average correlation between applicant perceptions and gender, age, and ethnic background was near zero. Face validity and perceived predictive validity were strong predictors of many applicant perceptions including procedural justice, distributive justice, attitudes towards tests, and attitudes towards selection. Interviews and work samples were perceived more favorably than cognitive ability tests, which were perceived more favorably than personality inventories, honesty tests, biodata, and graphology. The discussion identifies remaining theoretical and methodological issues as well as directions for future research. [source] Going Global: Cultural Values and Perceptions of Selection ProceduresAPPLIED PSYCHOLOGY, Issue 4 2009Ann Marie Ryan The role of cultural values in perceptions of selection tools is a concern of multinational corporations seeking to standardise staffing practices. Data from 1,199 individuals across 21 countries were gathered to examine the role of cultural values (independent and interdependent self-construals, achievement and ascription orientations) in perceptions of eight selection tools. Tool perceptions were mostly similar across individuals holding different cultural values, suggesting that multinational corporations may be able to construct tools with wide acceptability across cultures. Le rôle des valeurs culturelles dans l'appréhension des outils de sélection est une préoccupation des entreprises multinationales qui essaient de standardiser la gestion de leur personnel. On a rassemblé des données auprès de 1199 individus répartis sur 21 pays pour analyser le rôle des valeurs culturelles (conception de soi indépendante ou interdépendante, accomplissement et attributions) dans la représentation de huit outils de sélection. La perception de ces outils était le plus souvent analogue chez des personnes représentant des valeurs culturelles différentes, ce qui suppose que les multinationales sont à même d'élaborer des instruments utilisables quelle que soit la culture. [source] Student satisfaction with curriculum modifications in a French dental schoolEUROPEAN JOURNAL OF DENTAL EDUCATION, Issue 3 2000P. Farge Since 1994, important modifications have been implemented in the dental curriculum in France, and an additional year has been included in the dental curriculum. The 1st year has remained unchanged; it is common to both medical and dental schools and leads to a selection procedure of 1 in 10 dental students. In the new curriculum, the dental student is engaged in a 5-year programme in dental school (years 2 to 6), as opposed to 4 years in the former programme (years 2 to 5). Basically, this new curriculum emphasises research initiation, links with medical training and offers broader clinical experience. During the academic year 1998,1999, dental schools had 2 different types of students: the 4th year students belonging to the new programme along with the 5th year students in their final year of the old curriculum. Using a specially devised questionnaire, we investigated the students' perception of their respective training, their motivation and professional plans. At the Faculty of Odontology in Lyon, the new curriculum is perceived as an increased strain by the dental students. [source] Fuzzy based fast dynamic programming solution of unit commitment with ramp constraintsEXPERT SYSTEMS, Issue 4 2009S. Patra Abstract: A fast dynamic programming technique based on a fuzzy based unit selection procedure is proposed in this paper for the solution of the unit commitment problem with ramp constraints. The curse of dimensionality of the dynamic programming technique is eliminated by minimizing the number of prospective solution paths to be stored at each stage of the search procedure. Heuristics like priority ordering of the units, unit grouping, fast economic dispatch based on priority ordering, and avoidance of repeated economic dispatch through memory action have been employed to make the algorithm fast. The proposed method produced comparable results with the best performing methods found in the literature. [source] Analysis of single-locus tests to detect gene/disease associations,GENETIC EPIDEMIOLOGY, Issue 3 2005Kathryn Roeder Abstract A goal of association analysis is to determine whether variation in a particular candidate region or gene is associated with liability to complex disease. To evaluate such candidates, ubiquitous Single Nucleotide Polymorphisms (SNPs) are useful. It is critical, however, to select a set of SNPs that are in substantial linkage disequilibrium (LD) with all other polymorphisms in the region. Whether there is an ideal statistical framework to test such a set of ,tag SNPs' for association is unknown. Compared to tests for association based on frequencies of haplotypes, recent evidence suggests tests for association based on linear combinations of the tag SNPs (Hotelling T2 test) are more powerful. Following this logical progression, we wondered if single-locus tests would prove generally more powerful than the regression-based tests? We answer this question by investigating four inferential procedures: the maximum of a series of test statistics corrected for multiple testing by the Bonferroni procedure, TB, or by permutation of case-control status, TP; a procedure that tests the maximum of a smoothed curve fitted to the series of of test statistics, TS; and the Hotelling T2 procedure, which we call TR. These procedures are evaluated by simulating data like that from human populations, including realistic levels of LD and realistic effects of alleles conferring liability to disease. We find that power depends on the correlation structure of SNPs within a gene, the density of tag SNPs, and the placement of the liability allele. The clearest pattern emerges between power and the number of SNPs selected. When a large fraction of the SNPs within a gene are tested, and multiple SNPs are highly correlated with the liability allele, TS has better power. Using a SNP selection scheme that optimizes power but also requires a substantial number of SNPs to be genotyped (roughly 10,20 SNPs per gene), power of TP is generally superior to that for the other procedures, including TR. Finally, when a SNP selection procedure that targets a minimal number of SNPs per gene is applied, the average performances of TP and TR are indistinguishable. Genet. Epidemiol. © 2005 Wiley-Liss, Inc. [source] Latitudinal height couplings between single tropopause and 500 and 100 hPa within the Southern HemisphereINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 4 2010Adrián E. Yuchechen Abstract In order to provide further insights into the relationships between the tropopause and different mandatory levels, this paper discusses the coupling between standardized tropopause height anomalies (STHAs) and standardized 500-hPa and 100-hPa height anomalies (S5HAs and S1HAs, respectively) within the ,climatic year' for three sets of upper-air stations located approximately along 20°S, 30°S and 45°S. Data used in this research consists in a radiosonde database spanning the period 1973,2007. The mandatory levels are supposed to be included in each radiosonde profile. The tropopause, on the other hand, is calculated from the significant levels available for each sounding using the lapse rate definition. After applying a selection procedure, a basic statistical analysis combined with Fourier analysis is carried out in order to build up the standardized variables. Empirical orthogonal functions (EOFs) in S-mode are used to get the normal modes of oscillation as well as their time evolution, for STHA/S5HA as well as for STHA/S1HA coupling, separately, within the aforementioned latitudes. Overall, there are definite cycles in the time evolution associated with each EOF structure at all three latitudes, the semi-annual wave playing the most important role in most of the cases. Nevertheless, 20°S seems to be the only latitude driven by diabatic heating cycles in the middle atmosphere. Certainly, EOF1 at this latitude has a semi-annual behaviour and seems to be strongly influenced by the tropical convection seasonality. Apparently, the convectively driven release of latent heat in the middle troposphere affects the time evolution of the EOF1 structure. By contrast, the vertical propagation of planetary waves is raised as a possible explanation for the EOF1 and EOF2 behaviour at latitudes beyond 20°S, in view of the close connection existent between the semi-annual oscillation (SAO) and the reversion in the direction of the zonal wind. Copyright © 2009 Royal Meteorological Society [source] Performance evaluation of LIBTA/hybrid time-slot selection algorithm for cellular systems,INTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 6 2001Jyh-Horng Wen Abstract This paper studies the performance of radio assignment algorithms for portable access in cellular systems. Several channel access procedures are proposed and simulated using block oriented network simulator (BONeS) simulation of a model 36-port system. Simulation results exhibit that load-sharing system with LIBTA algorithm is better than directed retry system with the same algorithm by around 0.9 erlangs while better than quasi-fixed channel assignment (QFCA) system by around 2 erlangs if the grade of service (GOS) is constrained to less than 10 per cent. Plus, a hybrid time-slot selection procedure is proposed to enhance the system performance. It is observed that systems with hybrid time-slot selection perform better than those with LIBTA algorithm in GOS under heavy load. It is also observed that load sharing system with hybrid time-slot selection algorithm is better than directed retry system with the same algorithm by around 0.7 erlangs and better than QFCA system by around 2 erlangs. Copyright © 2001 John Wiley & Sons, Ltd. [source] Why do primary care doctors diagnose depression when diagnostic criteria are not met?INTERNATIONAL JOURNAL OF METHODS IN PSYCHIATRIC RESEARCH, Issue 3 2000Michael Höfler Abstract This study examines predictors of false positive depression diagnoses by primary care doctors in a sample of primary care attendees, taking the patients' diagnostic status from a self-report measure (Depression Screening Questionnaire, DSQ) as a yardstick against which to measure doctors' correct and false positive recognition rates. In a nationwide study, primary care patients aged 15,99 in 633 doctors' offices completed a self-report packet that included the DSQ, a questionnaire that assesses depression symptoms on a three-point scale to provide diagnoses of depression according to the criteria of DSM-IV and ICD-10. Doctors completed an evaluation form for each patient seen, reporting the patient's depression status, clinical severity, and treatment choices. Predictor analyses are based on 16,909 patient-doctor records. Covariates examined included depression symptoms, the total DSQ score, number and persistence of depression items endorsed, patient's prior treatment, history of depression, age and gender. According to the DSQ, 11.3% of patients received a diagnosis of ICD-10 depression, 58.9% of which were correctly identified by the doctor as definite threshold, and 26.2% as definite subthreshold cases. However, an additional 11.7% of patients not meeting the minimum DSQ threshold were rated by their doctors as definitely having depression (the false positive rate). Specific DSQ depression items endorsed, a higher DSQ total score, more two-week depression symptoms endorsed, female gender, higher age, and patient's prior treatment were all associated with an elevated rate of false positive diagnoses. The probability of false positive diagnoses was shown to be affected more by doctors ignoring the ,duration of symptoms' criterion than by doctors not following the ,number of symptoms' criterion for an ICD or DSM diagnosis of depression. A model selection procedure revealed that it is sufficient to regress the ,false positive diagnoses' on the DSQ-total score, symptoms of depressed mood, loss of interest, and suicidal ideation; higher age; and patient's prior treatment. Further, the total DSQ score was less important in prediction if there was a prior treatment. The predictive value of this model was quite good, with area under the ROC-curve = 0.86. When primary care doctors use depression screening instruments they are oversensitive to the diagnosis of depression. This is due to not strictly obeying the two weeks duration required by the diagnostic criteria of ICD-10 and DSM-IV. False positive rates are further increased in particular by the doctor's knowledge of a patient's prior treatment history as well as the presence of a few specific depression symptoms. Copyright © 2000 Whurr Publishers Ltd. [source] Is the Political Skill Inventory Fit for Personnel Selection?INTERNATIONAL JOURNAL OF SELECTION AND ASSESSMENT, Issue 2 2010An Experimental Field Study The political skill inventory (PSI) assesses social effectiveness in organizations by self-reports and has demonstrated strong evidence of validity. It was the purpose of this experimental field study to investigate construct and criterion-related validity of the PSI when used under conditions of personnel selection. In the experimental group (n=102), the instructions asked job incumbents to work on the PSI, a social desirability scale, and a Big-Five personality inventory as if they took part in a personnel selection procedure for a personally very attractive position. Additionally, they were asked to report yearly income. In the control group (n=110), job incumbents were asked to answer the items honestly. As expected, in both conditions, the PSI did not correlate with social desirability, but it correlated positively with extraversion, conscientiousness, and income, and negatively with neuroticism, thus demonstrating construct and incremental criterion-related validity under both conditions. Implications and limitations are discussed. [source] Candidates' Ability to Identify Criteria in Nontransparent Selection Procedures: Evidence from an assessment center and a structured interviewINTERNATIONAL JOURNAL OF SELECTION AND ASSESSMENT, Issue 3 2007Cornelius J. König In selection procedures like assessment centers (ACs) and structured interviews, candidates are often not informed about the targeted criteria. Previous studies have shown that candidates' ability to identify these criteria (ATIC) is related to their performance in the respective selection procedure. However, past research has studied ATIC in only one selection procedure at a time, even though it has been assumed that ATIC is consistent across situations, which is a prerequisite for ATIC to contribute to selection procedures' criterion-related validity. In this study, 95 candidates participated in an AC and a structured interview. ATIC scores showed cross-situational consistency across the two procedures and accounted for part of the relationship between performance in the selection procedures. Furthermore, ATIC scores in one procedure predicted performance in the other procedure even after controlling for cognitive ability. Implications and directions for future research are discussed. [source] Estimation of gonad volume, fecundity, and reproductive stage of shovelnose sturgeon using sonography and endoscopy with application to the endangered pallid sturgeonJOURNAL OF APPLIED ICHTHYOLOGY, Issue 4 2007By J. L. Bryan Summary Most species of sturgeon are declining in the Mississippi River Basin of North America including pallid (Scaphirhynchus albus F. and R.) and shovelnose sturgeons (S. platorynchus R.). Understanding the reproductive cycle of sturgeon in the Mississippi River Basin is important in evaluating the status and viability of sturgeon populations. We used non-invasive, non-lethal methods for examining internal reproductive organs of shovelnose and pallid sturgeon. We used an ultrasound to measure egg diameter, fecundity, and gonad volume; endoscope was used to visually examine the gonad. We found the ultrasound to accurately measure the gonad volume, but it underestimated egg diameter by 52%. After correcting for the measurement error, the ultrasound accurately measured the gonad volume but it was higher than the true gonad volume for stages I and II. The ultrasound underestimated the fecundity of shovelnose sturgeon by 5%. The ultrasound fecundity was lower than the true fecundity for stage III and during August. Using the endoscope, we viewed seven different egg color categories. Using a model selection procedure, the presence of four egg categories correctly predicted the reproductive stage ± one reproductive stage of shovelnose sturgeon 95% of the time. For pallid sturgeon, the ultrasound overestimated the density of eggs by 49% and the endoscope was able to view eggs in 50% of the pallid sturgeon. Individually, the ultrasound and endoscope can be used to assess certain reproductive characteristics in sturgeon. The use of both methods at the same time can be complementary depending on the parameter measured. These methods can be used to track gonad characteristics, including measuring Gonadosomatic Index in individuals and/or populations through time, which can be very useful when associating gonad characteristics with environmental spawning triggers or with repeated examinations of individual fish throughout the reproductive cycle. [source] COVPROC method: strategy in modeling dynamic systemsJOURNAL OF CHEMOMETRICS, Issue 2 2003Satu-Pia Reinikainen Abstract A new procedure to select subsets in sequential dynamic systems is presented. Subsets of variables and samples to be included in a PLS model are considered. The approach is a combination of PLS analysis and standard regression methods. It is based on the H-principle of mathematical modeling, and therefore the aim is to balance improvement in fit and precision. One of the main aspects in the subset selection procedure is to keep the score space as large and as sensible as possible to gain a stable model. The procedure is described mathematically and demonstrated for a dynamic industrial case. The method is simple to apply and the motivation of the procedure is obvious for industrial applications. It can be used e.g. when modeling on-line systems. Copyright © 2003 John Wiley & Sons, Ltd. [source] Selection of Value-at-Risk modelsJOURNAL OF FORECASTING, Issue 4 2003Mandira Sarma Abstract Value-at-Risk (VaR) is widely used as a tool for measuring the market risk of asset portfolios. However, alternative VaR implementations are known to yield fairly different VaR forecasts. Hence, every use of VaR requires choosing among alternative forecasting models. This paper undertakes two case studies in model selection, for the S&P 500 index and India's NSE-50 index, at the 95% and 99% levels. We employ a two-stage model selection procedure. In the first stage we test a class of models for statistical accuracy. If multiple models survive rejection with the tests, we perform a second stage filtering of the surviving models using subjective loss functions. This two-stage model selection procedure does prove to be useful in choosing a VaR model, while only incompletely addressing the problem. These case studies give us some evidence about the strengths and limitations of present knowledge on estimation and testing for VaR.,Copyright © 2003 John Wiley & Sons, Ltd. [source] Estimation of integrated squared density derivatives from a contaminated sampleJOURNAL OF THE ROYAL STATISTICAL SOCIETY: SERIES B (STATISTICAL METHODOLOGY), Issue 4 2002A. Delaigle Summary. We propose a kernel estimator of integrated squared density derivatives, from a sample that has been contaminated by random noise. We derive asymptotic expressions for the bias and the variance of the estimator and show that the squared bias term dominates the variance term. This coincides with results that are available for non-contaminated observations. We then discuss the selection of the bandwidth parameter when estimating integrated squared density derivatives based on contaminated data. We propose a data-driven bandwidth selection procedure of the plug-in type and investigate its finite sample performance via a simulation study. [source] On variable bandwidth selection in local polynomial regressionJOURNAL OF THE ROYAL STATISTICAL SOCIETY: SERIES B (STATISTICAL METHODOLOGY), Issue 3 2000Kjell Doksum The performances of data-driven bandwidth selection procedures in local polynomial regression are investigated by using asymptotic methods and simulation. The bandwidth selection procedures considered are based on minimizing ,prelimit' approximations to the (conditional) mean-squared error (MSE) when the MSE is considered as a function of the bandwidth h. We first consider approximations to the MSE that are based on Taylor expansions around h=0 of the bias part of the MSE. These approximations lead to estimators of the MSE that are accurate only for small bandwidths h. We also consider a bias estimator which instead of using small h approximations to bias naïvely estimates bias as the difference of two local polynomial estimators of different order and we show that this estimator performs well only for moderate to large h. We next define a hybrid bias estimator which equals the Taylor-expansion-based estimator for small h and the difference estimator for moderate to large h. We find that the MSE estimator based on this hybrid bias estimator leads to a bandwidth selection procedure with good asymptotic and, for our Monte Carlo examples, finite sample properties. [source] Using hyperspectral satellite imagery for regional inventories: a test with tropical emergent trees in the Amazon BasinJOURNAL OF VEGETATION SCIENCE, Issue 2 2010M. Pape Abstract Questions: Understanding distributions of tree species at landscape scales in tropical forests is a difficult task that could benefit from the recent development of satellite imaging spectroscopy. We tested an application of the EO-1 Hyperion satellite sensor to spectrally detect the location of five important tree taxa in the lowland humid tropical forests of southeastern Peru. Location: Peru, Departamento de Madre de Díos. Methods: We used linear discriminant analysis with a stepwise selection procedure to analyze two Hyperion datasets (July and December 2006) to choose the most informative narrow bands for classifying trees. Results: Optimal channels selected were different between the two seasons. Classification was 100% successful for the five taxa when using 25 narrow bands and pixels that represented >40% of tree crowns. We applied the discriminant functions developed separately for the two seasons to the entire study area, and found significantly nonrandom overlap in the anticipated distributions of the five taxa between seasons. Conclusions: Despite known issues, such as signal-to-noise ratio and spatial resolution, Hyperion imaging spectroscopy has potential for developing regional mapping of large-crowned tropical trees. [source] The ROSAT Brightest Cluster Sample , IV.MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2000The extended sample We present a low-flux extension of the X-ray-selected ROSAT Brightest Cluster Sample (BCS) published in Paper I of this series. Like the original BCS and employing an identical selection procedure, the BCS extension is compiled from ROSAT All-Sky Survey (RASS) data in the northern hemisphere (,,0°) and at high Galactic latitudes (|b|,20°). It comprises 99 X-ray-selected clusters of galaxies with measured redshifts z,0.3 (as well as eight more at z>0.3) and total fluxes between 2.8×10,12 and 4.4×10,12 erg cm,2 s,1 in the 0.1,2.4 keV band (the latter value being the flux limit of the original BCS). The extension can be combined with the main sample published in 1998 to form the homogeneously selected extended BCS (eBCS), the largest and statistically best understood cluster sample to emerge from the RASS to date. The nominal completeness of the combined sample (defined with respect to a power-law fit to the bright end of the BCS log N,log S distribution) is relatively low at 75 per cent (compared with 90 per cent for the high-flux sample of Paper I). However, just as for the original BCS, this incompleteness can be accurately quantified, and thus statistically corrected for, as a function of X-ray luminosity and redshift. In addition to its importance for improved statistical studies of the properties of clusters in the local Universe, the low-flux extension of the BCS is also intended to serve as a finding list for X-ray-bright clusters in the northern hemisphere which we hope will prove useful in the preparation of cluster observations with the next generation of X-ray telescopes such as Chandra and XMM-Newton. An electronic version of the eBCS can be obtained from the following URL: http://www.ifa.hawaii.edu/~ebeling/clusters/BCS.html. [source] A NOVEL METHOD OF FITTING SPATIO-TEMPORAL MODELS TO DATA, WITH APPLICATIONS TO THE DYNAMICS OF MOUNTAIN PINE BEETLESNATURAL RESOURCE MODELING, Issue 4 2008JUSTIN HEAVILIN Abstract We develop a modular landscape model for the mountain pine beetle (Dendroctonus ponderosae Hopkins) infestation of a stage-structured forest of lodgepole pine (Pinus contorta Douglas). Beetle attack dynamics are modeled using response functions and beetle movement using dispersal kernels. This modeling technique yields four model candidates. These models allow discrimination between four broad possibilities at the landscape scale: whether or not beetles are subject to an Allee effect at the landscape scale and whether or not host selection is random or directed. We fit the models with aerial damage survey data to the Sawtooth National Recreation Area using estimating functions, which allows for more rapid and complete parameter determination. We then introduce a novel model selection procedure based on facial recognition technology to compliment traditional nonspatial selection metrics. Together with these we are able to select a best model and draw inferences regarding the behavior of the beetle in outbreak conditions. [source] Electrocardiographic Activity before Onset of Postoperative Atrial Fibrillation in Cardiac Surgery PatientsPACING AND CLINICAL ELECTROPHYSIOLOGY, Issue 11 2008MIRELA OVREIU Ph.D. Background:Electrocardiographic (ECG) characteristics were analyzed in postoperative cardiac surgery patients in an attempt to predict development of new-onset postoperative atrial fibrillation (AF). Methods:Nineteen ECG characteristics were analyzed using computer-based algorithms. The parameters were retrospectively analyzed from ECG signals recorded in postoperative cardiac surgery patients while they were in the cardiovascular intensive care unit (CVICU) at our institution. ECG data from 99 patients (of whom 43 developed postoperative AF) were analyzed. A bootstrap variable selection procedure was applied to select the most important ECG parameters, and a multivariable logistic regression model was developed to classify patients who did and did not develop AF. Results:Premature atrial activity (PAC) was greater in AF patients (P < 0.01). Certain heart rate variability (HRV) and turbulence parameters also differed in patients who did and did not develop AF. In contrast, P-wave morphology was similar in patients with and without AF. Receiver operating curve (ROC) analysis applied to the model produced a C-statistic of 0.904. The model thus correctly classified AF patients with more than a 90% sensitivity and a 70% specificity. Conclusion:Among the 19 ECG parameters analyzed, PAC activity, frequency-domain HRV, and heart rate turbulence parameters were the best discriminators for postoperative AF. [source] Overexpression of the acidic dehydrin WCOR410 improves freezing tolerance in transgenic strawberry leavesPLANT BIOTECHNOLOGY JOURNAL, Issue 5 2004Mario Houde Summary Progress in freezing tolerance (FT) improvement through plant breeding approaches has met with little success in the last 50 years. Engineering plants for greater FT through plant transformation is one possible way to reduce the damage caused by freezing. Here, we report an improvement of the selection procedure and the transfer of the wheat Wcor410a acidic dehydrin gene in strawberry. The encoded protein has previously been shown to be associated with the plasma membrane, and its level of accumulation has been correlated with the degree of FT in different wheat genotypes. The WCOR410 protein was expressed in transgenic strawberry at a level comparable with that in cold-acclimated wheat. Freezing tests showed that cold-acclimated transgenic strawberry leaves had a 5 °C improvement of FT over wild-type or transformed leaves not expressing the WCOR410 protein. However, no difference in FT was found between the different plants under non-acclimated conditions, suggesting that the WCOR410 protein needs to be activated by another factor induced during cold acclimation. These data demonstrate that the WCOR410 protein prevents membrane injury and greatly improves FT in leaves of transgenic strawberry. A better understanding of the limiting factors allowing its activation may open up the way for engineering FT in different plant organs, and may find applications for the cryopreservation of human tissues and organs. [source] PARTIALLY LINEAR MODEL SELECTION BY THE BOOTSTRAPAUSTRALIAN & NEW ZEALAND JOURNAL OF STATISTICS, Issue 2 2009Samuel Müller Summary We propose a new approach to the selection of partially linear models based on the conditional expected prediction square loss function, which is estimated using the bootstrap. Because of the different speeds of convergence of the linear and the nonlinear parts, a key idea is to select each part separately. In the first step, we select the nonlinear components using an ,m -out-of- n' residual bootstrap that ensures good properties for the nonparametric bootstrap estimator. The second step selects the linear components from the remaining explanatory variables, and the non-zero parameters are selected based on a two-level residual bootstrap. We show that the model selection procedure is consistent under some conditions, and our simulations suggest that it selects the true model most often than the other selection procedures considered. [source] Markers of hepatitis B virus infection and immunity in Victoria, Australia, 1995 to 2005AUSTRALIAN AND NEW ZEALAND JOURNAL OF PUBLIC HEALTH, Issue 1 2010Benjamin Cowie Abstract Objective: Estimating the prevalence of chronic hepatitis B virus (HBV) infection in generally low-prevalence populations containing communities with a higher disease burden is difficult. This study was conducted to estimate the prevalence of serological markers of infection with, and immunity to, HBV in the Victorian population and to analyse trends in these estimates over time. Methods: A serological survey of 3,212 samples of convenience collected in the years 1995, 2000 and 2005 was conducted using a selection procedure designed to reduce selection bias. All samples were tested for hepatitis B surface and core antibodies; all core antibody positive samples (indicating previous infection) were then tested for the presence of hepatitis B surface antigen (HBsAg). Results: HBsAg prevalence was 1.1% (95%CI 0.8-1.6%) with significant differences observed by area of residence, age, gender and test year. Serological evidence of immunisation in infants and adolescents were lower than established estimates following the introduction of universal vaccination for these groups. Conclusions: This study emphasises the significant and growing problem of chronic HBV infection in Victoria and suggests lower than expected population immunity deriving from universal vaccination programs. Implications: Greater efforts are needed to formulate a comprehensive public health response to address this relatively neglected blood borne viral infection, the burden of which is very significant in some marginalised sections of our community. Increased attention to improving the universality of our immunisation programs is also needed. [source] Partly Functional Temporal Process Regression with Semiparametric Profile Estimating FunctionsBIOMETRICS, Issue 2 2009Jun Yan Summary Marginal mean models of temporal processes in event time data analysis are gaining more attention for their milder assumptions than the traditional intensity models. Recent work on fully functional temporal process regression (TPR) offers great flexibility by allowing all the regression coefficients to be nonparametrically time varying. The existing estimation procedure, however, prevents successive goodness-of-fit test for covariate coefficients in comparing a sequence of nested models. This article proposes a partly functional TPR model in the line of marginal mean models. Some covariate effects are time independent while others are completely unspecified in time. This class of models is very rich, including the fully functional model and the semiparametric model as special cases. To estimate the parameters, we propose semiparametric profile estimating equations, which are solved via an iterative algorithm, starting at a consistent estimate from a fully functional model in the existing work. No smoothing is needed, in contrast to other varying-coefficient methods. The weak convergence of the resultant estimators are developed using the empirical process theory. Successive tests of time-varying effects and backward model selection procedure can then be carried out. The practical usefulness of the methodology is demonstrated through a simulation study and a real example of recurrent exacerbation among cystic fibrosis patients. [source] Nonparametric Testing for DNA Copy Number Induced Differential mRNA Gene ExpressionBIOMETRICS, Issue 1 2009Wessel N. Van Wieringen Summary The central dogma of molecular biology relates DNA with mRNA. Array CGH measures DNA copy number and gene expression microarrays measure the amount of mRNA. Methods that integrate data from these two platforms may uncover meaningful biological relationships that further our understanding of cancer. We develop nonparametric tests for the detection of copy number induced differential gene expression. The tests incorporate the uncertainty of the calling of genomic aberrations. The test is preceded by a "tuning algorithm" that discards certain genes to improve the overall power of the false discovery rate selection procedure. Moreover, the test statistics are "shrunken" to borrow information across neighboring genes that share the same array CGH signature. For each gene we also estimate its effect, its amount of differential expression due to copy number changes, and calculate the coefficient of determination. The method is illustrated on breast cancer data, in which it confirms previously reported findings, now with a more profound statistical underpinning. [source] Exploratory Bayesian Model Selection for Serial Genetics DataBIOMETRICS, Issue 2 2005Jing X. Zhao Summary Characterizing the process by which molecular and cellular level changes occur over time will have broad implications for clinical decision making and help further our knowledge of disease etiology across many complex diseases. However, this presents an analytic challenge due to the large number of potentially relevant biomarkers and the complex, uncharacterized relationships among them. We propose an exploratory Bayesian model selection procedure that searches for model simplicity through independence testing of multiple discrete biomarkers measured over time. Bayes factor calculations are used to identify and compare models that are best supported by the data. For large model spaces, i.e., a large number of multi-leveled biomarkers, we propose a Markov chain Monte Carlo (MCMC) stochastic search algorithm for finding promising models. We apply our procedure to explore the extent to which HIV-1 genetic changes occur independently over time. [source] Decreased Expression of Bcl-x Protein during Hepatocarcinogenesis Induced Exogenously and Endogenously in RatsCANCER SCIENCE, Issue 12 2001Yutaka Hatanaka Dysregulations of apoptosis have been widely recognized as important events in multi-stage carcinogenesis. Bcl-x, a member of the Bcl-2 family, is known to act as a regulator of apoptosis. The present study was conducted to assess the role of altered Bcl-x protein expression in exogenous and endogenous hepatocarcinogenesis in rats. In the short-term exogenous models, male Fischer 344 rats, 6 weeks old, were given a single intraperitoneal injection of diethylnitrosamine (DEN) at a dose of 200 mg/kg body weight, partially hepatectomized at the end of week 3, administered phenobarbital at a concentration of 0.05% from the end of week 2 for 6 weeks, and sacrificed. In the livers, glutathione S-transferase (GST-P)-positive, putative preneoplastic lesions were induced, and Bcl-x protein expression was decreased in 24.7% of such lesions. The incidence of GST-P-positive lesions with decreased Bcl-x increased depending on the size of the lesions; 18.9%, 32.4% and 86.5% in the lesions smaller than 0.03, between 0.03 and 0.3, and larger than 0.3 mm2, respectively. In GST-P-positive lesions larger than 0.3 mm2, both apoptosis induction and cell proliferation activity were enhanced when Bcl-x protein expression was decreased. In the long-term exogenous models, rats were given 10 mg/kg of DEN, partially hepatectomized 4 h after treatment, administered 0.5 mg/kg of colchicine at the end of days 1 and 3, subjected to a selection procedure, and sacrificed at the end of week 45. Hepatocellular carcinomas were induced with the decreased Bcl-x protein expression. In the endogenous model, rats were fed a choline-deficient, l -amino acid-defined diet for 16 or 80 weeks and sacrificed. Bcl-x protein expression was decreased both in GST-P-positive lesions and hepatocellular carcinoma. These results suggest that this decrease of Bcl-x protein might serve as an indicator of the advanced form of preneoplastic lesions, and that this decrease could also be associated with a potential to progress into carcinoma in both exogenous and endogenous hepatocarcinogenesis of rats. [source] Forecasting daily high ozone concentrations by classification treesENVIRONMETRICS, Issue 2 2004F. Bruno Abstract This article proposes the use of classification trees (CART) as a suitable technique for forecasting the daily exceedance of ozone standards established by Italian law. A model is formulated for predicting, 1 and 2 days beforehand, the most probable class of the maximum daily urban ozone concentration in the city of Bologna. The standard employed is the so-called ,warning level' (180,,g/m3). Meteorological forecasted variables are considered as predictors. Pollution data show a considerable discrepancy between the dimensions of the two classes of events. The first class includes those days when the observed maximum value exceeds the established standard, while the second class contains those when the observed maximum value does not exceed the said standard. Due to this peculiarity, model selection procedures using cross-validation usually lead to overpruning. We can overcome this drawback by means of techniques which replicate observations, through the modification of their inclusion probabilities in the cross-validation sets. Copyright © 2004 John Wiley & Sons, Ltd. [source] | |||||||||||||||||||||||||||||||