bluuebunny/crossref_metadata_2025 huggingface dataset:
Accumulation of Calpain and Caspase-3 Proteolytic Fragments of Brain-Derived αII-Spectrin in Cerebral Spinal Fluid after Middle Cerebral Artery Occlusion in Rats
Authors: Pike Brian R. , Flint Jeremy , Dave Jitendra R. , Lu X.-C. May , Wang Kevin K.K. , Tortella Frank C. , Hayes Ronald L.
Published: December 2003

Preclinical studies have identified numerous neuroprotective drugs that attenuate brain damage and improve functional outcome after cerebral ischemia. Despite this success in animal models, neuroprotective therapies in the clinical setting have been unsuccessful. Identification of biochemical markers common to preclinical and clinical cerebral ischemia will provide a more sensitive and objective measure of injury severity and outcome to facilitate clinical management and treatment. However, there are currently no effective biomarkers available for assessment of stroke. Nonerythroid αII-spectrin is a cytoskeletal protein that is cleaved by calpain and caspase-3 proteases to signature αII-spectrin breakdown products (αII-SBDPs) after cerebral ischemia in rodents. This investigation examined accumulation of calpain- and caspase-3-cleaved αII-SBDPs in cerebrospinal fluid (CSF) of rodents subjected to 2 hours of transient focal cerebral ischemia produced by middle cerebral artery occlusion (MCAO) followed by reperfusion. After MCAO injury, full-length αII-spectrin protein was decreased in brain tissue and increased in CSF from 24 to 72 hours after injury. Whereas αII-SBDPs were undetectable in sham-injured control animals, calpain but not caspase-3 specific αII-SBDPs were significantly increased in CSF after injury. However, caspase-3 αII-SBDPS were observed in CSF of some injured animals. These results indicate that αII-SBDPs detected in CSF after injury, particularly those mediated by calpain, may be useful diagnostic indicators of cerebral infarction that can provide important information about specific neurochemical events that have occurred in the brain after acute stroke.
Induced Hippocampal Neuron Protection in an Optimized Gerbil Ischemia Model: Insult Thresholds for Tolerance Induction and Altered Gene Expression Defined by Ischemic Depolarization
Authors: Abe Hiroshi , Nowak Thaddeus S.
Published: December 2003

Preconditioning of hippocampal CA1 neurons was evaluated in a gerbil model of transient global ischemia using extracellular recording of DC potential shifts characteristic of ischemic depolarization to precisely define the duration of both priming and test insults. Brief ischemia resulting in depolarizations of 2.5 to 3.5 minutes consistently induced maximal tolerance (95% protection) against subsequent challenges 2 days later with an approximate doubling of the insult duration required for complete CA1 neuron loss from 6 to 12 minutes depolarization when evaluated 1 week after the test insult. Significant protection persisted at 2 months survival, although the apparent injury threshold regressed to approximately 8 minutes, indicating delayed progression of injury after longer test insults. In situ hybridization was used to evaluate depolarization thresholds for induction of mRNAs encoding the 70 kDa heat shock/stress protein, hsp72, as well as several immediate-early genes (c-fos, c-jun, junB, and junD). Immediate-early genes were prominently expressed after short insults inducing tolerance, whereas appreciable hsp72 induction only occurred after insults approaching the threshold for neuron injury. These results establish an ischemic preconditioning model with the predictability needed for mechanistic studies and demonstrate that prior transcriptional activation of the postischemic heat shock response is not required for expression of delayed tolerance.
Caspase Inhibition after Neonatal Ischemia in the Rat Brain
Authors: Joly Luc-Marie , Mucignat Valérie , Mariani Jean , Plotkine Michel , Charriaut-Marlangue Christiane
Published: December 2003

Caspase-3 has been identified as a key protease in the execution of apoptosis and appears to be an important downstream event after hypoxia-ischemia in the immature brain. The efficacy of a pan-caspase inhibitor, boc-aspartyl-(Ome)-fluoromethyl-ketone (BAF), was tested in a model of unilateral focal ischemia with reperfusion in 7-day-old rats. The BAF inhibitor was given intraperitoneally 5 minutes before reperfusion via the carotid artery. This procedure reduced the activity of caspase-3 by 79% but did not induce a significant reduction in infarct volume (23.8 ± 7.5% versus 30.1 ± 6.4%). Animals were distributed in two populations. One population exhibited an infarct, whereas the other appeared to be fully protected. BAF-treated animals exhibiting an infarct mostly displayed necrotic cell death, whereas apoptotic nuclei were observed in untreated or vehicle-treated animals. Repeated dose of BAF (5 minutes before and 9 hours after reperfusion) did not also provide benefit after neonatal ischemia, although a general trend to reduce lesion was observed (20.5 ± 3.7% versus 34.4 ± 5.9%). These findings raise critical questions about the use of peptide ketone apoptotic inhibitors in improving histopathologic outcomes after neonatal stroke.
Time Window of Fibroblast Growth Factor-18—Mediated Neuroprotection after Occlusion of the Middle Cerebral Artery in Rats*
Authors: Ellsworth Jeff L. , Garcia Richard , Yu Jin , Kindy Mark S.
Published: December 2003

To assess the time window for fibroblast growth factor-18 (FGF18)-mediated neuroprotection, FGF18 was administered by intravenous infusion at various times after transient occlusion of the middle cerebral artery (MCAO) in rats. Vehicle or FGF18 (100 μg·kg−1·h−1) was infused at 0.25, 0.5, 1.0, 2.0, 4.0, or 8.0 hours after MCAO with infarct volumes and behavioral deficits measured at 24.0 hours after MCAO. A separate group of animals received the infusions 24 hours after MCAO with endpoints measured at 48 hours after MCAO. Infusion of FGF18 reduced infarct volumes and improved scores in tests of reference and working memory, motor ability, and exploratory behavior. FGF18 was most efficacious when infused within 2 hours after MCAO. Significant reductions in infarct volumes and reductions in deficits of reference memory and motor activity were also observed with FGF18 infused 24 hours after MCAO. Measurements taken at infusion times before 2 hours after MCAO showed that regional cerebral blood flow was increased by FGF18. Administration of vehicle or FGF18 had no significant effect on mean arterial blood pressure, heart rate, brain temperature, blood pH, Pco2, or Po2. These results demonstrate that FGF18 is an effective neuroprotective agent when administered early after transient MCAO in rats. Efficacy observed with infusions at later times suggests an expanded time window for FGF18-mediated neuroprotection.
Coupling of Changes in Cerebral Blood Flow with Neural Activity: What Must Initially Dip Must Come Back Up
Authors: Ances Beau M.
Published: December 2003

Activation flow coupling, increases in neuronal activity leading to changes in cerebral blood flow (CBF), is the basis of many neuroimaging methods. An early rise in deoxygenation, the “initial dip,” occurs before changes in CBF and cerebral blood volume (CBV) and may provide a better spatial localizer of early neuronal activity compared with subsequent increases in CBF. Imaging modality, anesthetic, degree of oxygenation, and species can influence the magnitude of this initial dip. The observed initial dip may reflect a depletion of mitochondrial oxygen (O2) buffers caused by increased neuronal activity. Changes in CBF mediated by nitric oxide (NO) or other metabolites and not caused by a lack of O2 or energy depletion most likely lead to an increased delivery of capillary O2 in an attempt to maintain intracellular O2 buffers.
Caries on Permanent Teeth: A Non‐parametric Bayesian Analysis
Authors: Harkanen Tommi , Virtanen Jorma I. , Arjas Elja
Published: December 2003

Most earlier epidemiological investigations of dental caries have been based on cross‐sectional data. Subject‐specific information of dental caries in the past, and the duration of exposure of each tooth to the oral environment, are obviously important factors also influencing the presence of dental caries in the future. This has led us to consider multivariate survival models in which the information about the tooth eruption and failure times are combined to assess caries risk. A non‐parametric Bayesian intensity model is presented, reflecting, on the one hand, the within subject and between subject sources of variability, and a corresponding split of variability when considering the 28 permanent teeth. We analyse a data set consisting of the dental history of 240 boys, where the observations are based on predetermined dental examinations taking place approximately once every year. Markov chain Monte Carlo integration techniques are applied in the numerical work.
Sampling Bias in Population Studies—How to Use the Lexis Diagram
Authors: Lund Jens
Published: December 2003

Modified versions of the lifetime distribution are often used in survival analysis. The modifications depend on how we choose individuals for the study and on the assumptions on the behaviour of the population. A rigorous point process description of the Lexis diagram is used to make the sampling mechanisms and the preconditions transparent. The point process description gives a framework to handle all possible sampling patterns. The set‐up is generalized so it can handle more complicated life descriptions than just lifetimes, and the diability model is used as an example. Two set‐ups can be used. Conditional on the birthtimes, the lifetime distribution is left truncated and subject to either right censoring or right truncation. Assuming that the birthtimes can be described by a Poisson process the modifications are length bias and the recurrence time distribution known from renewal theory.
Analysis of Competing Risks by Using Bayesian Smoothing
Authors: Gasbarra Dario , Karia S. R.
Published: December 2003

We consider the competing risks set‐up. In many practical situations, the conditional probability of the cause of failure given the failure time is of direct interest. We propose to model the competing risks by the overall hazard rate and the conditional probabilities rather than the cause‐specific hazards. We adopt a Bayesian smoothing approach for both quantities of interest. Illustrations are given at the end.
A Non‐stationary Cox Model
Authors: Pons Odile , Visser Michael
Published: December 2003

The purpose of this paper is to consider the problem of statistical inference about a hazard rate function that is specified as the product of a parametric regression part and a non‐parametric baseline hazard. Unlike Cox's proportional hazard model, the baseline hazard not only depends on the duration variable, but also on the starting date of the phenomenon of interest. We propose a new estimator of the regression parameter which allows for non‐stationarity in the hazard rate. We show that it is asymptotically normal at root‐n and that its asymptotic variance attains the information bound for estimation of the regression coefficient. We also consider an estimator of the integrated baseline hazard, and determine its asymptotic properties. The finite sample performance of our estimators are studied.
Improving Ratio Estimators of Second Order Point Process Characteristics
Authors: Stoyan Dietrich , Stoyan Helga
Published: December 2003

Ripley's K function, the L function and the pair correlation function are important second order characteristics of spatial point processes. These functions are usually estimated by ratio estimators, where the numerators are Horvitz–Thompson edge corrected estimators and the denominators estimate the intensity or its square. It is possible to improve these estimators with respect to bias and estimation variance by means of adapted distance dependent intensity estimators. Further improvement is possible by means of refined estimators of the square of intensity. All this is shown by statistical analysis of simulated Poisson, cluster and hard core processes.
A Third Order Point Process Characteristic
Authors: Schladitz K. , Baddeley A. J.
Published: December 2003

Second order characteristics, in particular Ripley's K‐function, are widely used for the statistical analysis of point patterns. We examine a third order analogue, namely the mean number T(r) of r‐close triples of points per unit area. Equivalently this is the expected number of r‐close point pairs in an r‐neighbourhood of the typical point. Various estimators for this function are proposed and compared, and we give an explicit formula for the isotropic edge correction. The theoretical value of T seems to be unobtainable for most point process models apart from the homogeneous Poisson process. However, simulation studies show that the function T discriminates well between different types of point processes. In particular it detects a clear difference between the Poisson process and the Baddeley–Silverman cell process whereas the K‐functions for these processes coincide.
Autoregressive Forecasting of Some Functional Climatic Variations
Authors: Besse Philippe C. , Cardot Herve , Stephenson David B.
Published: December 2003

Many variations such as the annual cycle in sea surface temperatures can be considered to be smooth functions and are appropriately described using methods from functional data analysis. This study defines a class of functional autoregressive (FAR) models which can be used as robust predictors for making forecasts of entire smooth functions in the future. The methods are illustrated and compared with pointwise predictors such as SARIMA by applying them to forecasting the entire annual cycle of climatological El Nino–Southern Oscillation (ENSO) time series one year ahead. Forecasts for the period 1987–1996 suggest that the FAR functional predictors show some promising skill, compared to traditional scalar SARIMA forecasts which perform poorly.
Quasi‐likelihood Estimation of Non‐invertible Moving Average Processes
Authors: Huang Jian , Pawitan Yudi
Published: December 2003

Classical methods based on Gaussian likelihood or least‐squares cannot identify non‐invertible moving average processes, while recent non‐Gaussian results are based on full likelihood consideration. Since the error distribution is rarely known a quasi‐likelihood approach is desirable, but its consistency properties are yet unknown. In this paper we study the quasi‐likelihood associated with the Laplacian model, a convenient non‐Gaussian model that yields a modified L1 procedure. We show that consistency holds for all standard heavy tailed errors, but not for light tailed errors, showing that a quasi‐likelihood procedure cannot be applied blindly to estimate non‐invertible models. This is an interesting contrast to the standard results of the quasi‐likelihood in regression models, where consistency usually holds much more generally. Similar results hold for estimation of non‐causal non‐invertible ARMA processes. Various simulation studies are presented to validate the theory and to show the effect of the error distribution, and an analysis of the US unemployment series is given as an illustration.
Bayesian Analysis of a Growth Curve Model with a General Autoregressive Covariance Structure
Authors: Lee J. C. , Chang C. H.
Published: December 2003

In this paper we consider from maximum likelihood and Bayesian points of view the generalized growth curve model when the covariance matrix has a Toeplitz structure. This covariance is a generalization of the AR(1) dependence structure. Inferences on the parameters as well as the future values are included. The results are illustrated with several real data sets.
Simultaneous Confidence Bands and Hypothesis Testing in Varying‐coefficient Models
Authors: Fan Jianqing , Zhang Wenyang
Published: December 2003

Regression analysis is one of the most commonly used techniques in statistics. When the dimension of independent variables is high, it is difficult to conduct efficient non‐parametric analysis straightforwardly from the data. As an important alternative to the additive and other non‐parametric models, varying‐coefficient models can reduce the modelling bias and avoid the “curse of dimensionality” significantly. In addition, the coefficient functions can easily be estimated via a simple local regression. Based on local polynomial techniques, we provide the asymptotic distribution for the maximum of the normalized deviations of the estimated coefficient functions away from the true coefficient functions. Using this result and the pre‐asymptotic substitution idea for estimating biases and variances, simultaneous confidence bands for the underlying coefficient functions are constructed. An important question in the varying coefficient models is whether an estimated coefficient function is statistically significantly different from zero or a constant. Based on newly derived asymptotic theory, a formal procedure is proposed for testing whether a particular parametric form fits a given data set. Simulated and real‐data examples are used to illustrate our techniques.
Testing for No Effect by Cosine Series Methods
Authors: Eubank R. L.
Published: December 2003

The properties of three lack‐of‐fit tests that are related to non‐parametric cosine regression analysis are examined in the context of testing for a constant mean function. Analytic power comparisons of these tests vs a most powerful test are made using intermediate asymptotic relative efficiency. In particular, a data‐driven test is produced which is asymptotically as efficient as the most powerful test over a class of alternatives. A small scale simulation experiment is conducted to ascertain the extent that the large sample comparisons are applicable to finite samples.
Mismatch negativity in dichotic listening: Evidence for interhemispheric differences and multiple generators
Authors: Deouell Leon Y. , Bentin Shlomo , Giard Marie‐Helene
Published: December 2003

The characteristics of mismatch negativity (MMN) elicited by dichotic stimulation were examined using frequency‐deviant stimuli presented to the right, to the left, or to both sides. The experiment was run twice, once using earphones and once using loudspeakers in free field. With both modes of stimulation, deviants presented in the left, right, or both ears, or tones that were switched between ears, elicited comparable MMNs, with a peak latency of about 180 ms. With earphones, the amplitude of the MMN was bigger at the frontal‐lateral right hemisphere sites than at the homologous left‐hemisphere sites for all deviance conditions. Scalp current density analysis revealed that deviance in the right side elicited bilaterally equivalent frontal current sinks and a trend towards stronger contralateral current sources at the mastoid sites. In contrast, left side deviance elicited frontal sinks and temporal current sources stronger over the right hemiscalp. These results are compatible with the multiple‐generator model of MMN. The attention‐related role of the MMN is discussed, suggesting comparable attention mechanisms for vision and audition.
On the automaticity of ipsilateral response activation in the Simon effect
Authors: Valle‐Inclán Fernando , Redondo Milagros
Published: December 2003

The effects on performance of unattended stimulus–response spatial relationships in choice reaction time tasks (i.e., the Simon effect) have been attributed to automatic activation of the response ipsilateral to stimulus location. We tested this assumption using the lateralized readiness potential (LRP). The response key labels changed randomly from trial to trial and were presented either 400 ms before (immediate‐reaction trials) or 400 ms after (delayed‐reaction trials) stimulus. The critical test for the automatic activation hypothesis was on delayed‐reaction trials, in which LRP deflections were expected in the interval between stimulus and response‐key labels. Contrary to this prediction, there were no LRP signs of response activation within that interval.
Frontal brain asymmetry and affective style: A conceptual replication
Authors: Hagemann Dirk , Naumann Ewald , Becker Gabriele , Maier Stefanie , Bartussek Dieter
Published: December 2003

Recent studies have demonstrated that positive and negative affective reactivity can be predicted by resting electroencephalographic (EEG) asymmetry in frontal brain regions. These studies used different methods to assess asymmetry and affectivity. The goal of the present study was a conceptual replication of these results and to investigate their independence of employed procedures. Resting EEG of 37 subjects was recorded and affective slides were presented to obtain ratings of subjects' emotional reactions. Different procedures were applied to the data to assess the relation between asymmetries and affective reactivity. Depending on the particular analysis procedure, there were associations between anterior asymmetry and affectivity in line with the published findings, opponent to those findings, or no relation between anterior asymmetry and affective reactivity.
Resting frontal electroencephalographic asymmetry in depression: Inconsistencies suggest the need to identify mediating factors
Authors: Reid Stephanie A. , Duke Lisa M. , Allen John J.B.
Published: December 2003

Two studies of the relationship between depression and resting frontal electroencephalographic (EEG) activity are reported. Although considerable research supports the theory of left and right hemispheric specialization for approach and withdrawal behaviors, only four studies involving clinically depressed individuals have been published to date. Despite methodological similarities with published research, no significant differences in frontal activation emerged between depressed and nondepressed participants with either college students having high Beck Depression Inventory scores (Study 1) or with individuals diagnosed with DSM‐III‐R depression (Study 2). Post hoc analyses in Study 2 revealed one effect confined to lateral frontal leads during the first 2 min of EEG data; this finding was significant in only one of three reference montages. Results are discussed in light of methodological considerations and mediating variables such as temperament and coping styles.
Automatic change detection: Does the auditory system use representations of individual stimulus features or gestalts?
Authors: Deacon Diana , Nousak Jo Manette , Pilotti Maura , Ritter Walter , Yang Chien‐Ming
Published: December 2003

The effects of global and feature‐specific probabilities of auditory stimuli were manipulated to determine their effects on the mismatch negativity (MMN) of the human event‐related potential. The question of interest was whether the automatic comparison of stimuli indexed by the MMN was performed on representations of individual stimulus features or on gestalt representations of their combined attributes. The design of the study was such that both feature and gestalt representations could have been available to the comparator mechanism generating the MMN. The data were consistent with the interpretation that the MMN was generated following an analysis of stimulus features.
Influence of respiratory activity on the cardiac response pattern to mental effort
Authors: Althaus Monika , Mulder Lambertus J.M. , Mulder Gijsbertus , van Roon Arie M. , Minderaa Ruud B.
Published: December 2003

A group of 32 healthy adult volunteers completed three blocks of a reaction time task that varied in the degree of controlled processing load. A rest period preceded each of the task blocks. The task blocks were presented in the order of either increasing or decreasing cognitive load. For each of the six periods, mean values and spectral measures of heart rate and respiration variability were calculated. The spectral measures were obtained for three different frequency bands. Differences between the cardiac measures of the task and preceding rest periods were compared with respect to differences in task load and the order of task presentation. All comparisons were carried out while adjusting for respiratory variability in the corresponding frequency band. The frequency band in which task load‐related changes in heart rate variability became manifest appeared to be dependent on the individual's breathing pattern.
Maternal exposure to influenza in pregnancy and electrodermal activity in offspring: A further study from Mauritius
Authors: Venables Peter H.
Published: December 2003

This study examined the effect of mothers' exposure to the 1957 A2/Singapore influenza virus in the first, second, and third trimesters of pregnancy on the electrodermal activity of their 15‐year‐old offspring. The epidemic occurred during cold months of the year. The results show that maternal viral (and cold) exposure during all trimesters of pregnancy produced a lower frequency of nonspecific electrodermal responses and diminished responsivity to 75‐db and 90‐db tones as compared with the offspring of mothers who were not exposed. However, there was a critical effect of second trimester exposure as indicated by an increase in frequency of nonresponses to orienting tones. The findings are compared with those from an earlier study from Mauritius involving 3‐year‐old children in which the effects of exposure to the 1968 A2/Hong Kong virus were examined and in which the effect of cold exposure could be examined separately because viral exposure occurred during the hot months.
A longitudinal analysis of eye tracking dysfunction and attention in recent‐onset schizophrenia
Authors: Yee Cindy M. , Nuechterlein Keith H. , Dawson Michael E.
Published: December 2003

The effect of an attentional manipulation on eye tracking dysfunction (ETD) in the early stages of schizophrenia was examined in 34 recent‐onset schizophrenic patients and 24 demographically matched normal subjects over a 1‐year period. An attentional enhancement manipulation improved eye tracking performance of recent‐onset schizophrenic patients more than that of normal subjects. Eye tracking level also was moderately stable for both groups over the course of 1 year. The possible role of attentional allocation in ETD highlights the need for further examination of the interface between attentional and eye tracking measures of vulnerability to schizophrenia.
Effects of stimulus modality and task condition on blink startle modification and on electrodermal responses
Authors: Lipp Ottmar V. , Siddle David A.T. , Dall Patricia J.
Published: December 2003

Participants in Experiments 1 and 2 performed a discrimination and counting task to assess the effect of lead stimulus modality on attentional modification of the acoustic startle reflex. Modality of the discrimination stimuli was changed across subjects. Electrodermal responses were larger during task‐relevant stimuli than during task‐irrelevant stimuli in all conditions. Larger blink magnitude facilitation was found during auditory and visual task‐relevant stimuli, but not for tactile stimuli. Experiment 3 used acoustic, visual, and tactile conditioned stimuli (CSs) in differential conditioning with an aversive unconditioned stimulus (US). Startle magnitude facilitation and electrodermal responses were larger during a CS that preceded the US than during a CS that was presented alone regardless of lead stimulus modality. Although not unequivocal, the present data pose problems for attentional accounts of blink modification that emphasize the importance of lead stimulus modality.
Physiological response to a minimal social encounter: Effects of gender, ethnicity, and social context
Authors: Vrana Scott R. , Rollock David
Published: December 2003

This study examined physiological response to an encounter with and touch by an unfamiliar person. Fifty‐five African American (23 male, 30 female) and 51 European American (23 male, 28 female) undergraduates participated. A Black or White interactor entered the room, introduced himself or herself, checked equipment for 30 s, and then took a pulse for 30 s. Entry of the interactor resulted in increased corrugator and zygomaticus facial muscle activity (EMG), increased skin conductance (SC), and heart rate (HR) acceleration. Corrugator EMG was greater among Black subjects; White subjects responded with more zygomatic EMG and SC and greater HR acceleration. Women showed a more positive facial expression than did men. Being touched reduced EMG and HR but resulted in increased SC. White and Black males showed more HR acceleration when encountering a Black male interactor.
Testing treatment effects in repeated measures designs: An update for psychophysiological researchers
Authors: Keselman H.J.
Published: December 2003

In 1987, Jennings enumerated data analysis procedures that authors must follow for analyzing effects in repeated measures designs when submitting papers to Psychophysiology. These prescriptions were intended to counteract the effects of nonspherical data, a condition know to produce biased tests of significance. Since this editorial policy was established, additional refinements to the analysis of these designs have appeared in print in a number of sources that are not likely to be routinely read by psychophysiological researchers. Accordingly, this paper includes additional procedures not previously enumerated in the editorial policy that can be used to analyze repeated measurements. Furthermore, I indicate how numerical solutions can easily be obtained.
8. Assessing the Effect of Model Misspecifications on Parameter Estimates in Structural Equation Models
Authors: Yuan Ke-Hai , Marshall Linda L. , Bentler Peter M.
Published: December 2003

Model misspecifications may have a systematic effect on parameters, causing biases in their estimates. In the application of structural equation models, every interesting model is fallible. When simultaneously evaluating a model, it is of interest to study whether all parameters are affected by a misspecification. This paper provides three procedures for evaluating such an effect: (1) analyzing the path, (2) using a functional relationship, and (3) using a significance test. Analyzing the path is illustrated through a confirmatory factor model. This method is ad hoc but intuitive. A more rigorous approach is built upon the concept of orthogonality of two sets of parameters. When parameter a is orthogonal to parameter b, omitting parameter b will not affect the estimation of parameter a. The functional relationship of two sets of parameters is used to check their orthogonality. The distribution of the difference between estimates based on different models is obtained, which provides a Hausman-like way to check significant parameter differences that are due to biases. Examples illustrate that these procedures can provide valuable information on identifying parameter estimates that are systematically affected by a model misspecification.
9. Model Fit in Structural Equation Models with Censored, Ordinal, and Dichotomous Variables: Testing Vanishing Tetrads
Authors: Hipp John R. , Bollen Kenneth A.
Published: December 2003

Although the methodology for handling ordinal and dichotomous observed variables in structural equation models (SEMs) is developing rapidly, several important issues are unresolved. One of these is the optimal test statistic to apply as a test of overall model fit. We propose a new “vanishing tetrad” test statistic for such models. We build on Bollen's (1990) simultaneous test statistic for testing multiple vanishing tetrads and on Bollen and Ting's (1993) confirmatory tetrad analysis (CTA) for hypothesis testing of model structures. These and other works on vanishing tetrads assume continuous observed variables and do not consider observed categorical variables. In this paper we present a method to test models when some or all of the observed variables are collapsed or categorical versions of underlying continuous variables. The test statistic that we provide is an alternative “overall fit” statistic for SEMs with censored, ordinal, or dichotomous observed variables. Furthermore, the vanishing tetrad test sometimes permits us to compare the fit of some models that are not nested in the traditional likelihood ratio test. We illustrate the new test statistic with examples and a small simulation experiment comparing it with two other tests of model fit for SEMs with ordinal or dichotomous endogenous variables.
10. Settings in Social Networks: A Measurement Model
Authors: Schweinberger Michael , Snijders Tom A. B.
Published: December 2003

A class of statistical models is proposed that aims to recover latent settings structures in social networks. Settings may be regarded as clusters of vertices. The measurement model is based on two assumptions. (1) The observed network is generated by hierarchically nested latent transitive structures, expressed by ultrametrics, and (2) the expected tie strength decreases with ultrametric distance. The approach could be described as model-based clustering with an ultrametric space as the underlying metric to capture the dependence in the observations. Bayesian methods as well as maximum-likelihood methods are applied for statistical inference. Both approaches are implemented using Markov chain Monte Carlo methods.
1. Overcoming the Reference Category Problem in the Presentation of Statistical Models
Authors: Firth David
Published: December 2003

Effects of categorical variables in statistical models typically are reported in terms of comparison either with a reference category or with a suitably defined “mean effect,” for reasons of parameter identification. A conventional presentation of estimates and standard errors, but without the full variance-covariance matrix, does not allow subsequent readers either to make inference on a comparison of interest that is not presented or to compare or combine results from different studies where the same variables but different reference levels are used. It is shown how an alternative presentation, in terms of “quasi standard errors,” overcomes this problem in an economical and intuitive way. A primary application is the reporting of effects of categorical predictors, often called factors, in linear and generalized linear models, hazard models, multinomial-response models, generalized additive models, etc. Other applications include the comparison of coefficients between related regression equations—for example, log-odds ratios in a multinomial logit model—and the presentation of multipliers or “scores” in models with multiplicative interaction structure.
4. Accelerated Failure-Time Mover-Stayer Regression Models for the Analysis of Last-Episode Data
Authors: Yamaguchi Kazuo
Published: December 2003

This article introduces new models for the analysis of last-episode data—that is, data about the timing of the last occurrence of a repeatable event. The new models are elaborations and extensions of a particular model for backward recurrence times from a renewal process introduced by Allison (1985), and they are accelerated failure-time mover-stayer regression models that permit the separation of covariate effects on event timing from those on event occurrence. Using the data of last residential move from the 1990 Census of Population and Housing, an application of the models, which are found to fit the data adequately, shows distinct patterns in the effects of home ownership, gender, race/ethnicity, education, marital experience, and age group on residential mobility. The patterns differ regarding the relative importance and direction of influence between the effects on the duration of residence in the same house or apartment and the effects on the lifetime probability of not experiencing any residential move.
6. A Multivariate, Multilevel Rasch Model with Application to Self-Reported Criminal Behavior
Authors: Raudenbush Stephen W. , Johnson Christopher , Sampson Robert J.
Published: December 2003

In studying correlates of social behavior, attitudes, and beliefs, a measurement model is required to combine information across a large number of item responses. Multiple constructs are often of interest, and covariates are often multilevel (e.g., measured at the person and neighborhood level). Some item-level missing data can be expected. This paper proposes a multivariate, multilevel Rasch model with random effects for these purposes and illustrates its application to self-reports of criminal behavior. Under assumptions of conditional independence and additivity, the approach enables the investigator to calibrate the items and persons on an interval scale, assess reliability at the person and neighborhood levels, study the correlations among crime types at each level, assess the proportion of variation in each crime type that lies at each level, incorporate covariates at each level, and accommodate data missing at random. Using data on 20 item responses from 2842 adolescents ages 9 to 18 nested within 196 census tracts in Chicago, we illustrate how to test key assumptions, how to adjust the model in light of diagnostic analyses, and how to interpret parameter estimates.
7. Multilevel Latent Class Models
Authors: Vermunt Jeroen K.
Published: December 2003

The latent class (LC) models that have been developed so far assume that observations are independent. Parametric and non-parametric random-coefficient LC models are proposed here, which will make it possible to modify this assumption. For example, the models can be used for the analysis of data collected with complex sampling designs, data with a multilevel structure, and multiple-group data for more than a few groups. An adapted EM algorithm is presented that makes maximum-likelihood estimation feasible. The new model is illustrated with examples from organizational, educational, and cross-national comparative research.
Breeding success in Blue Tits: good territories or good parents?
Authors: Przybylo Robert , Wiggins David A. , Merilä Juha
Published: December 2003

Territorial quality and parental quality are usually assumed to be the main sources of variation in the reproductive success of passerine birds. To evaluate their relative importance for variation in breeding time (itself an important factor for breeding success), clutch size and offspring condition at fledging, we analysed six years of data from a Blue Tit Parus caeruleus population breeding on the island of Gotland, Sweden. Hatching dates and the condition of offspring were consistent for territories between years and accounted for 30% and 33% of the variation in these variables, respectively. After removing the effect of territory quality, none of the breeding parameters were significantly repeatable for individual females, but offspring condition was repeatable for males, accounting for 28% of variation. For females breeding on the same territory in subsequent seasons (combined effect of individual and territory quality) only hatching date was repeatable (45% of variation accounted for). In males, the combined effect of individual and territory quality was repeatable for offspring condition and accounted for 33% of variation, but this result was only marginally significant. Consistency of the peak frass‐fall date for individual frass collectors over the study period suggests that repeatable hatching dates on territories may be related to the relationship between timing of breeding and timing of peak food availability on territories. Our results suggest that territory quality is more important than parental quality for breeding success in the Blue Tit, and that male (but not female) quality makes a considerable contribution to reproductive success.
Sex‐biased hatching sequences in the cooperatively breeding Noisy Miner
Authors: Arnold Kathryn E. , Griffith Simon C. , Goldizen Anne W.
Published: December 2003

The Noisy Miner Manorina melanocephala (Meliphagidae) is a cooperatively breeding bird species in which sons often remain on their natal home ranges and help one or both of their parents. In a population of Noisy Miners in SE Queensland, Australia, a molecular technique was used to explore adult and offspring sex ratios, and also hatching sequences. Among the adult population, there were 2.31 males for every female, and roughly 99% of helping was performed by males. At hatching and fledging, the population sex ratio was even, with exactly 57 males and 57 females. However, in 17 out of 18 broods the first egg to hatch was male. First‐hatched males were significantly larger and heavier than their sisters just prior to fledging. Through their helping behaviour, large healthy sons could clearly enhance the future reproductive success of parents, and benefit the entire group. Sex‐biased hatching sequences could potentially provide cooperatively breeding birds with a subtle and precise way of varying investment in the helping sex.
How to hatch from an egg of great structural strength. A study of the Common Cuckoo
Authors: Honza Marcel , Picman Jaroslav , Grim Tomáš , Novák Vít , Čapek, Jr. Miroslav , Mrlík Vojtěch
Published: December 2003

Brood parasitism represents a unique mode of avian reproduction that requires a number of adaptations. For example, to reduce chances of puncture ejection of their eggs by small hosts, brood parasites may have been selected for laying eggs of unusually great structural strength. However, great structural strength of eggshells should hinder hatching. The goals of our study were to establish if chicks of the Common Cuckoo Cuculus canorus have more difficulty with hatching out of their strong eggs than chicks of species with eggs of similar size, and whether they possess any mechanisms facilitating hatching. To achieve these goals, we compared hatching pattern and selected body characteristics of chicks of the Common Cuckoo with those of another altricial species with eggs of a similar size, the Great Reed Warbler Acrocephalus arundinaceus. Although the rate of pecking was similar in the two species, the Common Cuckoo chicks started pecking earlier in relation to their emergence and consequently required more time and a greater cumulative number of pecks for breaking open their eggs than did young Great Reed Warblers. The two species also differed with respect to the pattern of opening their shells; in contrast to the warbler chicks, which enlarged the original pip circularly, the cuckoo chicks opened the egg by systematically creating a long narrow slit until they emerged. Finally, our study of hatched young revealed several differences; the Cuckoo hatchlings were significantly heavier, had a longer forearm, and their egg tooth was located significantly farther from the tip of the beak. The edge used for cutting through the shell was also significantly longer than that of hatchling Great Reed Warblers. To conclude, our data suggest that hatching is more difficult for a Cuckoo than for a Great Reed Warbler and that Cuckoos possess several mechanisms to overcome the problems of hatching from a structurally strong egg.
Turnover of territorial Scops Owls Otus scops as estimated by spectrographic analyses of male hoots
Authors: Galeotti Paolo , Sacchi Roberto
Published: December 2003

In this study we assessed territory turnover of the European Scops Owl Otus scops, a migratory nocturnal raptor, using sonagrams of hoots recorded in the same territories in the 1993 and 1994 breeding seasons. Three structural parameters of the hoot (duration, inter‐note interval and frequency) varied considerably, and a Discriminant Function Analysis classified >90% of individual calls correctly. In order to investigate yearly turnover and site‐fidelity of male Scops Owls, the discriminant functions derived from the hoot sample recorded in 1993 were used to classify hoots of individuals recorded in the same territories in 1994. Apparently, turnover rate of territory owners was high and rapid, because 55–78% of territories censused in 1993 were defended by a different male in 1994. The fast decline of our Scops Owl population, probably due to winter mortality, could be responsible for such a high turnover of territorial owners.
Feather mites on birds: costs of parasitism or conditional outcomes?
Authors: Blanco Guillermo , Tella José L. , Potti Jaime , Baz Arturo
Published: December 2003

Feather mites (suborder Astigmata, superfamilies Analgoidea, Pterolichoidea and Freyaniidae) are among the commonest ectosymbionts of birds. Most researchers have assumed they are parasites, having negative effects on hosts. Here we present evidence that suggests that feather mites may not be parasites. We develop a framework for considering conditional outcomes in these interspecific associations, dealing with different kinds of relationships between symbionts. The non‐parasitic status of feather mites is supported by a literature review as well as by preliminary data on mites’ food. We illustrate symbiotic relationships with a graphical model showing different scenarios in which hosts’ cost‐benefit relations are determined by the interactions among their symbionts.
Seed preferences by birds: effects of the design of feeding‐preference experiments
Authors: Cueto Víctor R. , Marone Luis , De Casenave Javier Lopez
Published: December 2003

We analysed the effects of the design of feeding‐preference experiments in a study of seed selection by Rufous‐collared Sparrows Zonotrichia capensis. We presented eight seed options in multiple‐ and simple‐offer experiments. Statistical results indicated that in multiple‐offer tests there were three preferred, and two avoided seed species. The other three species could not be assigned to any of those groups. In contrast, results of simple‐offer tests showed that all seed species were preferred, except the two avoided ones. Using a graphical combination of the results of both approaches, we obtained an easily interpretable assessment of the seed preferences of Rufous‐collared Sparrows. In the graph space, seed species make up three groups: preferred, avoided, and less‐preferred (i.e., heavily consumed in simple‐offer trials, but avoided or consumed to a lesser extent in multiple‐offer trials). With the combination of both protocols we avoided the biases caused by using one experimental design alone and could detect secondary‐preferred food items. This seems crucial when the bird under study is plastic in its feeding preferences.
Factors affecting nesting success of a bird assembly in the central Monte Desert, Argentina
Authors: Mezquida Eduardo T. , Marone Luis
Published: December 2003

We estimated nesting success of a breeding bird assemblage in the central Monte Desert in four breeding seasons (1995–1999). We analyzed the effect of year, period within the breeding season, nest type, and nest location on daily survival rates (DSR). Averaged nesting success of passeriforms in natural habitats was very low (<20% on average, n=12 species). DSR tended to be lower during the egg‐laying stage in Furnariidae, Rhinocryptidae, Mimidae, and Emberizidae. Tyrannidae had the highest DSR for all nesting stages and Emberizidae the lowest. Predation was the main cause of nest failure (>90% on average, n=12 species). DSR differed among years, being higher in the driest year (1995) and lower in the most humid year (1997). Nests initiated in the first half of the breeding season had higher DSR than those initiated in the second half. Closed nests had similar survival rates to open nests. DSR differed according to species of plant that supported the nest. Nest predation in the central Monte Desert may be an important selective pressure in birds’ life history, which is in accordance with other results for South American temperate birds.