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Covariance
Kinds of Covariance Terms modified by Covariance Selected AbstractsMULTILEVEL SELECTION AND THE PARTITIONING OF COVARIANCE: A COMPARISON OF THREE APPROACHESEVOLUTION, Issue 3 2004Samir Okasha Abstract Where the evolution of a trait is affected by selection at more than one hierarchical level, it is often useful to compare the magnitude of selection at each level by asking how much of the total evolutionary change is attributable to each level of selection. Three statistical partitioning techniques, each designed to answer this question, are compared, in relation to a simple multilevel selection model in which a trait's evolution is affected by both individual and group selection. None of the three techniques is wholly satisfactory: one implies that group selection can operate even if individual fitness is determined by individual phenotype alone, whereas the other two imply that group selection can operate even if there is no variance in group fitness. This has significant implications both for our understanding of what the term "multilevel selection" means and for the traditional concept of group selection. [source] GENETIC VARIATION IN MALE EFFECTS ON FEMALE REPRODUCTION AND THE GENETIC COVARIANCE BETWEEN THE SEXESEVOLUTION, Issue 6 2003MARY ELLEN CZESAK Abstract., Males of many insect species increase the fecundity and/or egg size of their mates through the amount or composition of their nuptial gifts or ejaculate. The genetic bases of such male effects on fecundity or egg size are generally unknown, and thus their ability to evolve remains speculative. Likewise, the genetic relationship between male and female investment into reproduction in dioecious species, which is expected to be positive if effects on fecundity are controlled by at least some of the same genes in males and females, is also unknown. Males of the seed beetle Stator limbatus contribute large ejaculates to females during mating, and the amount of donated ejaculate is positively correlated with male body mass. Females mated to large males lay more eggs in their lifetime than females mated to small males. We describe an experiment in which we quantify genetic variation in the number of eggs sired by males (mated to a single female) and found that a significant proportion of the phenotypic variance in the number of eggs sired by males was explained by their genotype. Additionally, the number of eggs sired by a male was highly positively genetically correlated with his body mass. The between-sex genetic correlation, that is, the genetic correlation between the number of eggs sired by males and the number of eggs laid by females, was highly positive when eggs were laid on Acacia greggii seeds. This indicates that males that sire many eggs have sisters that lay many eggs. Thus, some of the genes that control male ejaculate size (or some other fecundity-enhancing factor) when expressed in males appear to control fecundity when expressed in females. We found no significant interaction between male and female genotype on fecundity. [source] ROBUST OUTPUT FEEDBACK CONTROLLER DESIGN WITH COVARIANCE AND DISC CLOSED-LOOP POLE CONSTRAINTSASIAN JOURNAL OF CONTROL, Issue 3 2005Li Yu ABSTRACT This paper is concerned with the problem of robust output feedback controller design for a class of linear discrete-time systems with normbounded uncertainty. The objective is to design a controller such that the closed-loop poles are assigned within a specified disc and the steady regulated output covariance is guaranteed to be less than a given upper bound. Using a linear matrix inequality (LMI) approach, the existence conditions of such controllers are derived, and a parametrized characterization of a set of desired controllers (if they exist) is presented in terms of the feasible solutions to a set of LMIs. A procedure is given to select a suitable output feedback controller that minimizes the desired control effort. [source] Evaluation of a wind erosion model in a desert area of northern Asia by eddy covarianceEARTH SURFACE PROCESSES AND LANDFORMS, Issue 13 2009Gerardo Fratini Abstract For the first time, vertical fluxes of mineral dust measured by Eddy Covariance in two desert sites of Northern Asia have been used to test the performances of a wind erosion model in the field. Soil parameters required by the model were obtained through field and laboratory determinations. Model predictions and direct measurements have been compared. The main finding was that the direction of the horizontal wind relative to the orientation of nebkhas played a crucial role in determining the emission of particles in one of the investigated sites. Being unable to simulate such interaction, the model generally overestimated the actual emission. It provided, instead, reliable predictions (r2 = 0·87) when the wind direction was suitable in detaching loose erodible elements placed on nebkhas thanks to their normal orientation. Copyright © 2009 John Wiley & Sons, Ltd. [source] Covariance-based subdivision of the human striatum using T1-weighted MRIEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 6 2008Michael X Cohen Abstract The striatum plays a key role in many cognitive and emotional processes, and displays an intricate pattern of connectivity with cortical and subcortical structures. Invasive tracing work in rats and non-human primates demonstrates that the striatum can be segregated into subregions based on similar clustering of input and output fibers. In contrast, the human striatum is typically segregated according to local anatomical landmarks without considering natural boundaries formed by functional/anatomical networks. Here, we used non-invasive magnetic resonance (MR) imaging in young, healthy adults to define subregions of the human striatum based on volume correlations with other subcortical and cortical structures. We present three methods to delineate anatomical volumetric correlations based on gray matter content estimated from T1-weighted MR images. We observed both consistencies with and divergences from invasive tracing work in animals, suggesting that magnetic resonance imaging (MRI)-based covariance likely does not correspond to direct anatomical connections, although it might index other forms of connectivity or tissue type similarity. These novel approaches may be useful in understanding connectivity of other regions, and changes in connectivity in patient or ageing populations. [source] Test of Nyborg's General Trait Covariance (GTC) model for hormonally guided development by means of structural equation modelingEUROPEAN JOURNAL OF PERSONALITY, Issue 3 2003Martin Reuter Nyborg's General Trait Covariance (GTC) model for hormonally guided development investigates the influence of gonadal hormones and fluid intelligence on body build, achievement, and socioeconomic variables. According to the model, testosterone should be negatively related to height, fat/muscle ratio, intelligence, income, and education. It is conceived that this influence should be determined to a great extent by mutual relationships between these variables. The model was tested by means of structural equation modeling (SEM) in a sample of 4375 males who had served in the United States Armed Forces. The results largely confirm Nyborg's androtype model but in addition reflect the relationships between the variables included in a quantitative causal manner. It could be shown that testosterone has a negative influence on crystallized intelligence and that this effect is mainly mediated by the negative influence of testosterone on education. An additional multiple group analysis testing for structural invariance across age groups revealed that the mediating role of education is more pronounced in old veterans. Copyright © 2002 John Wiley & Sons, Ltd. [source] Covariance of tricarboxylate carrier activity and lipogenesis in liver of polyunsaturated fatty acid (n-6) fed ratsFEBS JOURNAL, Issue 22 2001Vincenzo Zara The mitochondrial tricarboxylate (citrate) carrier plays an important role in hepatic intermediary metabolism because, among other functions, it supplies the cytosol with acetyl units for fatty-acid synthesis. In this study, the effect of polyunsaturated fatty acids (PUFA, n-6) on the function of this mitochondrial transporter and on lipogenic enzyme activities was investigated by feeding rats for 4 weeks with a 15%-fat diet composed of high linoleic safflower oil. Citrate transport was strongly reduced in liver mitochondria isolated from PUFA-treated rats. A reduced transport activity was also observed when solubilized mitochondrial citrate carrier from PUFA-treated rats was reconstituted into liposomes. In the same animals, a decrease of cytosolic lipogenic enzyme activities was observed. These results indicate a coordinated modulation of citrate carrier and of lipogenic enzyme activities by PUFA feeding. Kinetic analysis of the carrier activity showed that only Vmax decreased, whereas Km was almost virtually unaffected. The PUFA-mediated effect is most likely due to the reduced mRNA level and lower content of the citrate carrier protein observed in the safflower oil-fed rats. [source] Brain structure and obesityHUMAN BRAIN MAPPING, Issue 3 2010Cyrus A. Raji Abstract Obesity is associated with increased risk for cardiovascular health problems including diabetes, hypertension, and stroke. These cardiovascular afflictions increase risk for cognitive decline and dementia, but it is unknown whether these factors, specifically obesity and Type II diabetes, are associated with specific patterns of brain atrophy. We used tensor-based morphometry (TBM) to examine gray matter (GM) and white matter (WM) volume differences in 94 elderly subjects who remained cognitively normal for at least 5 years after their scan. Bivariate analyses with corrections for multiple comparisons strongly linked body mass index (BMI), fasting plasma insulin (FPI) levels, and Type II Diabetes Mellitus (DM2) with atrophy in frontal, temporal, and subcortical brain regions. A multiple regression model, also correcting for multiple comparisons, revealed that BMI was still negatively correlated with brain atrophy (FDR <5%), while DM2 and FPI were no longer associated with any volume differences. In an Analysis of Covariance (ANCOVA) model controlling for age, gender, and race, obese subjects with a high BMI (BMI > 30) showed atrophy in the frontal lobes, anterior cingulate gyrus, hippocampus, and thalamus compared with individuals with a normal BMI (18.5,25). Overweight subjects (BMI: 25,30) had atrophy in the basal ganglia and corona radiata of the WM. Overall brain volume did not differ between overweight and obese persons. Higher BMI was associated with lower brain volumes in overweight and obese elderly subjects. Obesity is therefore associated with detectable brain volume deficits in cognitively normal elderly subjects. Hum Brain Mapp, 2010. © 2009 Wiley-Liss, Inc. [source] Book review: Analysis of Variance and Covariance: How to Choose and Construct Models for the Life SciencesAMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY, Issue 4 2009Benjamin M. Auerbach No abstract is available for this article. [source] On Efficiency of Constrained Longitudinal Data Analysis Versus Longitudinal Analysis of CovarianceBIOMETRICS, Issue 3 2010Kaifeng Lu Summary:, In randomized clinical trials, measurements are often collected on each subject at a baseline visit and several post-randomization time points. The longitudinal analysis of covariance in which the postbaseline values form the response vector and the baseline value is treated as a covariate can be used to evaluate the treatment differences at the postbaseline time points. Liang and Zeger (2000,,Sankhy,: The Indian Journal of Statistics, Series B,62, 134,148) propose a constrained longitudinal data analysis in which the baseline value is included in the response vector together with the postbaseline values and a constraint of a common baseline mean across treatment groups is imposed on the model as a result of randomization. If the baseline value is subject to missingness, the constrained longitudinal data analysis is shown to be more efficient for estimating the treatment differences at postbaseline time points than the longitudinal analysis of covariance. The efficiency gain increases with the number of subjects missing baseline and the number of subjects missing all postbaseline values, and, for the pre,post design, decreases with the absolute correlation between baseline and postbaseline values. [source] Analysis of Variance and Covariance: How to Choose and Construct Models for the Life Sciences by DONCASTER, C. P. and DAVEY, A. J. H.BIOMETRICS, Issue 1 2009Article first published online: 17 MAR 200 No abstract is available for this article. [source] Varying Coefficient Model with Unknown Within-Subject Covariance for Analysis of Tumor Growth CurvesBIOMETRICS, Issue 4 2008Robert T. Krafty Summary In this article we develop a nonparametric estimation procedure for the varying coefficient model when the within-subject covariance is unknown. Extending the idea of iterative reweighted least squares to the functional setting, we iterate between estimating the coefficients conditional on the covariance and estimating the functional covariance conditional on the coefficients. Smoothing splines for correlated errors are used to estimate the functional coefficients with smoothing parameters selected via the generalized maximum likelihood. The covariance is nonparametrically estimated using a penalized estimator with smoothing parameters chosen via a Kullback,Leibler criterion. Empirical properties of the proposed method are demonstrated in simulations and the method is applied to the data collected from an ovarian tumor study in mice to analyze the effects of different chemotherapy treatments on the volumes of two classes of tumors. [source] Estimating Systematic Risk Using Time Varying DistributionsEUROPEAN FINANCIAL MANAGEMENT, Issue 1 2002Gregory Koutmos This article proposes a dynamic vector GARCH model for the estimation of time-varying betas. The model allows the conditional variances and the conditional covariance between individual portfolio returns and market portfolio returns to respond asymmetrically to past innovations depending on their sign. Covariances tend to be higher during market declines. There is substantial time variation in betas but the evidence on beta asymmetry is mixed. Specifically, in 50% of the cases betas are higher during market declines and for the remaining 50% the opposite is true. A time series analysis of estimated time varying betas reveals that they follow stationary mean-reverting processes. The average degree of persistence is approximately four days. It is also found that the static market model overstates non-market or, unsystematic risk by more than 10%. On the basis of an array of diagnostics it is confirmed that the vector GARCH model provides a richer framework for the analysis of the dynamics of systematic risk. [source] Bayesian inference strategies for the prediction of genetic merit using threshold models with an application to calving ease scores in Italian Piemontese cattleJOURNAL OF ANIMAL BREEDING AND GENETICS, Issue 4 2002K. Kizilkaya Summary First parity calving difficulty scores from Italian Piemontese cattle were analysed using a threshold mixed effects model. The model included the fixed effects of age of dam and sex of calf and their interaction and the random effects of sire, maternal grandsire, and herd-year-season. Covariances between sire and maternal grandsire effects were modelled using a numerator relationship matrix based on male ancestors. Field data consisted of 23 953 records collected between 1989 and 1998 from 4741 herd-year-seasons. Variance and covariance components were estimated using two alternative approximate marginal maximum likelihood (MML) methods, one based on expectation-maximization (EM) and the other based on Laplacian integration. Inferences were compared to those based on three separate runs or sequences of Markov Chain Monte Carlo (MCMC) sampling in order to assess the validity of approximate MML estimates derived from data with similar size and design structure. Point estimates of direct heritability were 0.24, 0.25 and 0.26 for EM, Laplacian and MCMC (posterior mean), respectively, whereas corresponding maternal heritability estimates were 0.10, 0.11 and 0.12, respectively. The covariance between additive direct and maternal effects was found to be not different from zero based on MCMC-derived confidence sets. The conventional joint modal estimates of sire effects and associated standard errors based on MML estimates of variance and covariance components differed little from the respective posterior means and standard deviations derived from MCMC. Therefore, there may be little need to pursue computation-intensive MCMC methods for inference on genetic parameters and genetic merits using conventional threshold sire and maternal grandsire models for large datasets on calving ease. Zusammenfassung Die Kalbeschwierigkeiten bei italienischen Piemonteser Erstkalbskühen wurden mittels eines gemischten Threshold Modells untersucht. Im Modell wurden die fixen Einflüsse vom Alter der Kuh und dem Geschlecht des Kalbes, der Interaktion zwischen beiden und die zufälligen Effekte des Großvaters der Mutter und der Herden-Jahr-Saisonklasse berücksichtigt. Die Kovarianz zwischen dem Vater der Kuh und dem Großvater der Mutter wurde über die nur auf väterlicher Verwandtschaft basierenden Verwandtschaftsmatrix berücksichtigt. Es wurden insgesamt 23953 Datensätze aus den Jahren 1989 bis 1998 von 4741 Herden-Jahr-Saisonklassen ausgewertet. Die Varianz- und Kovarianzkomponenten wurden mittels zweier verschiedener approximativer marginal Maximum Likelihood (MML) Methoden geschätzt, die erste basierend auf Expectation-Maximierung (EM) und die zweite auf Laplacian Integration. Rückschlüsse wurden verglichen mit solchen, basierend auf drei einzelne Läufe oder Sequenzen von Markov Chain Monte Carlo (MCMC) Stichproben, um die Gültigkeit der approximativen MML Schätzer aus Daten mit ähnlicher Größe und Struktur zu prüfen. Die Punktschätzer der direkten Heritabilität lagen bei 0,24; 0,25 und 0,26 für EM, Laplacian und MCMC (Posterior Mean), während die entsprechenden maternalen Heritabilitäten bei 0,10, 0,11 und 0,12 lagen. Die Kovarianz zwischen dem direkten additiven und dem maternalen Effekt wurden als nicht von Null verschieden geschätzt, basierend auf MCMC abgeleiteten Konfidenzintervallen. Die konventionellen Schätzer der Vatereffekte und deren Standardfehler aus den MML-Schätzungen der Varianz- und Kovarianzkomponenten differieren leicht von denen aus der MCMC Analyse. Daraus folgend besteht wenig Bedarf die rechenintensiven MCMC-Methoden anzuwenden, um genetische Parameter und den genetischen Erfolg zu schätzen, wenn konventionelle Threshold Modelle für große Datensätze mit Vätern und mütterlichen Großvätern mit Kalbeschwierigkeiten genutzt werden. [source] Validation and Clinical Utility of a Simple In-Home Testing Tool for Sleep-Disordered Breathing and Arrhythmias in Heart Failure: Results of the Sleep Events, Arrhythmias, and Respiratory Analysis in Congestive Heart Failure (SEARCH) StudyCONGESTIVE HEART FAILURE, Issue 5 2006William T. Abraham MD Fifty patients with New York Heart Association class III systolic heart failure were enrolled in this prospective multicenter study that compared the diagnostic accuracy of a home-based cardiorespiratory testing system with standard attended polysomnography. Patients underwent at least 2 nights of evaluation and were scored by blinded observers. At diagnostic cutoff points of ,5, ,10, and ,15 events per hour for respiratory disturbance severity, polysomnography demonstrated a sleep-disordered breathing prevalence of 69%, 59%, and 49%, respectively. Compared with polysomnography, the cardiorespiratory testing system demonstrated predictive accuracies of 73%, 73%, and 75%, which improved to 87%, 87%, and 83%, respectively, when analysis of covariance suggested reanalysis omitting one site's data. The system accurately identified both suspected and unsuspected arrhythmias. The device was judged by 80% of patients to be easy or very easy to use, and 74% of patients expressed a preference for the in-home system. Therefore, this system represents a reasonable home testing device in these patients. [source] Developing an attitude towards bullying scale for prisoners: structural analyses across adult men, young adults and women prisonersCRIMINAL BEHAVIOUR AND MENTAL HEALTH, Issue 1 2009Jane L. Ireland Background,Few studies have attempted to explore attitudes towards bullying among prisoners, despite acknowledgement that attitudes may play an important role. Aim,To evaluate the structure of a new attitudinal scale, the Prison Bullying Scale (PBS), with adult men and women in prison and with young male prisoners. Hypotheses,That attitudes would be represented as a multidimensional construct and that the PBS structure would be replicated across confirmatory samples. Method,The PBS was developed and confirmed across four independent studies using item parceling and confirmatory factor analysis: Study I comprised 412 adult male prisoners; Study II, 306 adult male prisoners; Study III, 171 male young offenders; and Study IV, 148 adult women prisoners. Results,Attitudes were represented as a multidimensional construct comprising seven core factors. The exploratory analysis was confirmed in adult male samples, with some confirmation among young offenders and adult women. The fit for young offenders was adequate and improved by factor covariance. The fit for women was the poorest overall. Conclusion,The study notes the importance of developing ecologically valid measures and statistically testing these measures prior to their clinical or research use. Implications,The development of the PBS holds value both as an assessment and as a research measure and remains the only ecologically validated measure in existence to assess prisoner attitudes towards bullying. Copyright © 2009 John Wiley & Sons, Ltd. [source] Preventing depression: a randomized trial of interpersonal psychotherapy-adolescent skills training,DEPRESSION AND ANXIETY, Issue 5 2010Jami F. Young Ph.D. Abstract Background: The study evaluated the efficacy of an indicated prevention program for adolescent depression. Methods: Fifty-seven adolescents with elevated depression symptoms were randomized to receive Interpersonal Psychotherapy-Adolescent Skills Training (IPT-AST) or school counseling (SC). Hierarchical linear modeling examined differences in rates of change in depression symptoms and overall functioning and analysis of covariance examined mean differences between groups. Rates of depression diagnoses in the 18-month follow-up period were compared. Results: Adolescents in IPT-AST reported significantly greater rates of change in depression symptoms and overall functioning than SC adolescents from baseline to post-intervention. At post-intervention, IPT-AST adolescents reported significantly fewer depression symptoms and better overall functioning. During the follow-up phase, rates of change slowed for the IPT-AST adolescents, whereas the SC adolescents continued to show improvements. By 12-month follow-up, there were no significant mean differences in depression symptoms or overall functioning between the two groups. IPT-AST adolescents reported significantly fewer depression diagnoses in the first 6 months following the intervention but by 12-month follow-up the difference in rates of diagnoses was no longer significant. Conclusions: IPT-AST leads to an immediate reduction in depression symptoms and improvement in overall functioning. However, the benefits of IPT-AST are not consistent beyond the 6-month follow-up, suggesting that the preventive effects of the program in its current format are limited. Future studies are needed to examine whether booster sessions lengthen the long-term effects of IPT-AST. Depression and Anxiety, 2010. © 2010 Wiley-Liss, Inc. [source] Early response and 8-week treatment outcome in GAD ,DEPRESSION AND ANXIETY, Issue 8 2006Moira Rynn M.D. Abstract Our objective was to compare the predictive value of early response to treatment outcome in patients with generalized anxiety disorder (GAD) treated with benzodiazepines, serotonin receptor (5HT-1A) partial agonists, or placebo. Data from two double-blind GAD studies were combined. Subjects were evaluated with the Hamilton Anxiety Scale (HAM-A) and the Clinical Global Impression of Improvement (CGI-I) scale over 8 weeks. Categories of response at weeks 1 and 2 were defined by the HAM-A total score. Analyses of covariance and Kaplan,Meier survival analyses were the primary analyses used to assess 8-week end point treatment outcomes as a function of early improvement. HAM-A change from baseline to weeks 1 and 2 significantly predicted last observation carried forward (LOCF) response at week 8 for both medications and for placebo (P<.001). Early improvement was a strong predictor for treatment outcome irrespective of whether active medication or placebo was the treatment agent. Depression and Anxiety 23:461,465, 2006. Published 2006 Wiley-Liss, Inc. [source] A randomized controlled trial of the impact of therapeutic horse riding on the quality of life, health, and function of children with cerebral palsyDEVELOPMENTAL MEDICINE & CHILD NEUROLOGY, Issue 2 2009E DAVIS PHD This randomized controlled trial examined whether therapeutic horse riding has a clinically significant impact on the physical function, health and quality of life (QoL) of children with cerebral palsy (CP). Ninety-nine children aged 4 to 12 years with no prior horse riding experience and various levels of impairment (Gross Motor Function Classification System Levels I,III) were randomized to intervention (10wks therapeutic programme; 26 males, 24 females; mean age 7y 8mo [SD 2y 5mo] or control (usual activities, 27 males, 22 females; mean age 8y 2mo [SD 2y 6mo]). Pre- and post-measures were completed by 72 families (35 intervention and 37 control). Children's gross motor function (Gross Motor Function Measure [GMFM]), health status (Child Health Questionnaire [CHQ]), and QoL (CP QoL-Child, KIDSCREEN) were assessed by parents and QoL was assessed by children before and after the 10-week study period. On analysis of covariance, there was no statistically significant difference in GMFM, CP QoL-Child (parent report and child self-report), and CHQ scores (except family cohesion) between the intervention and control group after the 10-week study period, but there was weak evidence of a difference for KIDSCREEN (parent report). This study suggests that therapeutic horse riding does not have a clinically significant impact on children with CP. However, a smaller effect cannot be ruled out and the absence of evidence might be explained by a lack of sensitivity of the instruments since the QoL and health measures have not yet been demonstrated to be sensitive to change for children with CP. [source] Improved cardiovascular health following a progressive walking and dietary intervention for type 2 diabetesDIABETES OBESITY & METABOLISM, Issue 9 2009S. T. Johnson Aim: To examine the impact of two different lifestyle programmes on cardiovascular health and glycaemic control among people with type 2 diabetes. Methods: A two-phase 24-week randomized trial. During the first phase, participants were to increase daily steps using a pedometer. At week 12, participants were randomly allocated to either an enhanced lifestyle programme (ELP) targeting walking speed or a basic lifestyle programme (BLP) targeting total daily steps. Both programmes focused on increasing the intake of low glycaemic index foods but utilized different goal setting strategies. Clinical measurements were completed at baseline, week 12 and week 24. Principal outcomes were change in resting pulse rate (PR) and glycated haemoglobin A1c (A1c) between week 12 and week 24 compared between groups using analysis of covariance. Results: Forty-one participants [mean ± s.d. : age = 56.5 ± 7.2 years, body mass index (BMI) = 32.7 ± 6.1 kg/m2] were randomized. After 12 weeks, we observed an increase in average total daily steps of 1562 (95% confidence interval: 303,2821, p = 0.02). Weight, BMI and systolic and diastolic blood pressure improved (p < 0.01 for all). No changes were observed for energy intake. At week 24, those in the ELP had a lower resting PR (71 ± 12 b.p.m.) compared with those in the BLP (78 ± 12 b.p.m.) (adjusted p = 0.03), while no group differences for total daily steps or glycaemic control were observed. Conclusions: Improvements in cardiovascular health can be expected following a pedometer-based lifestyle modification programme that progresses from walking more to walking faster. [source] Socio-economic status, obesity and prevalence of Type 1 and Type 2 diabetes mellitusDIABETIC MEDICINE, Issue 6 2000J. M. M. Evans Summary Aims ,The influence of socio-economic status on the prevalence of Type 1 and Type 2 diabetes mellitus, and on obesity, was explored using routinely collected healthcare data for the population of Tayside, Scotland. Methods ,Among 366 849 Tayside residents, 792 and 5474 patients with Type 1 and Type 2 diabetes, respectively, were identified from a diabetes register. The Carstairs Score was used as a proxy for socio-economic status. This is a material deprivation measure derived from the UK census, using postcode data for four key variables. Odds ratios for diabetes prevalence, adjusted for age, were determined for each of six deprivation categories (1 , least deprived, 6/7 , most deprived). The mean body mass index (BMI) in each group was also determined, and the effect of deprivation category explored by analysis of covariance, adjusting for age and sex. Results ,The prevalence of Type 2 diabetes, but not Type 1 diabetes, varied by deprivation. People in deprivation category 6 and 7 were 1.6-times (95% confidence interval 1.4,1.8) more likely to have Type 2 diabetes than those least deprived. There was no relationship between deprivation and BMI in Type 1 diabetes (P = 0.36), but there was an increase in BMI with increasing deprivation in Type 2 diabetes (P < 0.001; test of linearity P < 0.001). Conclusions ,The study confirms the relationship between deprivation and the prevalence of Type 2 diabetes. There are more obese, diabetic patients in deprived areas. They require more targeted resources and more primary prevention. [source] Heterogeneity, speciation/extinction history and climate: explaining regional plant diversity patterns in the Cape Floristic RegionDIVERSITY AND DISTRIBUTIONS, Issue 3 2002R. M. Cowling Abstract. This paper investigates the role of heterogeneity and speciation/extinction history in explaining variation in regional scale (c. 0.1,3000 km2) plant diversity in the Cape Floristic Region of south-western Africa, a species- and endemic-rich biogeographical region. We used species-area analysis and analysis of covariance to investigate geographical (east vs. west) and topographic (lowland vs. montane) patterns of diversity. We used community diversity as a surrogate for biological heterogeneity, and the diversity of naturally rare species in quarter degree squares as an indicator of differences in speciation/extinction histories across the study region. We then used standard statistical methods to analyse geographical and topographic patterns of these two measures. There was a clear geographical diversity pattern (richer in the west), while a topographic pattern (richer in mountains) was evident only in the west. The geographical boundary coincided with a transition from the reliable winter-rainfall zone (west) to the less reliable non-seasonal rainfall zone (east). Community diversity, or biological heterogeneity, showed no significant variation in relation to geography and topography. Diversity patterns of rare species mirrored the diversity pattern for all species. We hypothesize that regional diversity patterns are the product of different speciation and extinction histories, leading to different steady-state diversities. Greater Pleistocene climatic stability in the west would have resulted in higher rates of speciation and lower rates of extinction than in the east, where for the most, Pleistocene climates would not have favoured Cape lineages. A more parsimonious hypothesis is that the more predictable seasonal rainfall of the west would have favoured non-sprouting plants and that this, in turn, resulted in higher speciation and lower extinction rates. Both hypotheses are consistent with the higher incidence of rare species in the west, and higher levels of beta and gamma diversity there, associated with the turnover of species along environmental and geographical gradients, respectively. These rare species do not contribute to community patterns; hence, biological heterogeneity is uniform across the region. The weak topography pattern of diversity in the west arises from higher speciation rates and lower extinction rates in the topographically complex mountains, rather than from the influence of environmental heterogeneity on diversity. [source] Evaluation of a wind erosion model in a desert area of northern Asia by eddy covarianceEARTH SURFACE PROCESSES AND LANDFORMS, Issue 13 2009Gerardo Fratini Abstract For the first time, vertical fluxes of mineral dust measured by Eddy Covariance in two desert sites of Northern Asia have been used to test the performances of a wind erosion model in the field. Soil parameters required by the model were obtained through field and laboratory determinations. Model predictions and direct measurements have been compared. The main finding was that the direction of the horizontal wind relative to the orientation of nebkhas played a crucial role in determining the emission of particles in one of the investigated sites. Being unable to simulate such interaction, the model generally overestimated the actual emission. It provided, instead, reliable predictions (r2 = 0·87) when the wind direction was suitable in detaching loose erodible elements placed on nebkhas thanks to their normal orientation. Copyright © 2009 John Wiley & Sons, Ltd. [source] Ecohydrology of a semi-arid forest: partitioning among water balance components and its implications for predicted precipitation changesECOHYDROLOGY, Issue 2 2010Naama Raz Yaseef Abstract The distribution of precipitation inputs into different hydrological components of water-limited forest ecosystems determines water availability to trees and consequently forest productivity. We constructed a complete hydrological budget of a semi-arid pine forest (285 mm annual precipitation) by directly measuring its main components: precipitation (P), soil water content, evapotranspiration (ET, eddy covariance), tree transpiration (sap flux), soil evaporation (soil chambers), and intercepted precipitation (calculated). Our results indicated that on average for the 4-year study period, ET accounted for 94% of P, varying between 100% when P < 250 mm and 85% when P > 300 mm (with indications for losses to subsurface flow and soil moisture storage in wetter years). Direct measurements of the components of the ET flux demonstrated that both transpiration and soil evaporation were significant in this dry forest (45% and 36% of ET, respectively). Comparison between ecosystem ET (eddy covariance measurements) and the sum of its measured components showed good agreement on annual scales, but up to 30% discrepancies (in both directions) on shorter timescales. The pulsed storm pattern, characteristics of semi-arid climates, was sufficient to maintain the topsoil layer wet during the whole wet season. Only less often and intensive storms resulted in infiltration to the root zone, increasing water availability for uptake by deeper roots. Our results indicate that climate change predictions that link reduced precipitation with increased storm intensity may have a smaller effect on water availability to forest ecosystems than reduced precipitation alone, which could help forests' survival and maintain productivity even under drier conditions. Copyright © 2009 John Wiley & Sons, Ltd. [source] Smaller amphipod mothers show stronger trade-offs between offspring size and numberECOLOGY LETTERS, Issue 2 2000Douglas S. Glazier Trade-offs between embryo mass and number were studied in 10 populations of the freshwater amphipod Gammarus minus. Trade-offs were stronger in populations with small brooding females than in those with larger brooding females. Relationships between embryo mass and maternal body mass were also stronger in populations dominated by small versus large brooding females. These patterns are likely the result of morphological constraints, at least in part. Embryo size is more affected by brood size and maternal size in small mothers, probably because of offspring-packaging constraints associated with small brood pouches. Energy constraints appear to be less important. These results suggest that body size may not only affect the magnitude of individual life-history traits, as is well known, but also the covariance between traits. [source] Efficiency, Equilibrium, and Asset Pricing with Risk of DefaultECONOMETRICA, Issue 4 2000Fernando Alvarez We introduce a new equilibrium concept and study its efficiency and asset pricing implications for the environment analyzed by Kehoe and Levine (1993) and Kocherlakota (1996). Our equilibrium concept has complete markets and endogenous solvency constraints. These solvency constraints prevent default at the cost of reducing risk sharing. We show versions of the welfare theorems. We characterize the preferences and endowments that lead to equilibria with incomplete risk sharing. We compare the resulting pricing kernel with the one for economies without participation constraints: interest rates are lower and risk premia depend on the covariance of the idiosyncratic and aggregate shocks. Additionally, we show that asset prices depend only on the valuation of agents with substantial idiosyncratic risk. [source] Entrepreneurial Scripts and the New Transaction Commitment Mindset: Extending the Expert Information Processing Theory Approach to Entrepreneurial Cognition ResearchENTREPRENEURSHIP THEORY AND PRACTICE, Issue 4 2009J. Brock Smith In this study, we extend the expert information processing theory approach to entrepreneurial cognition research through an empirical exploration of the new transaction commitment mindset among business people in Canada, Mexico, and the United States. Using analysis of covariance, multivariate analysis of variance, and hierarchical regression analysis of data from a cross-sectional sample of 417 respondents, our results provide a foundation for additional cross-level theory development, with related implications for increasing the practicality of expert information processing theory-based entrepreneurial cognition research. Specifically, this paper: (1) clarifies the nature of the relationship between entrepreneurial expert scripts and constructs that might represent an entrepreneurial mindset at the individual level of analysis; (2) identifies analogous relationships at the economy level of analysis, where the structure found at the individual level informs an economy-level problem; (3) presents a North American Free Trade Agreement-based illustration analysis to demonstrate the extent to which cognitive findings at the individual level can be used to explain economy-level phenomena; and (4) extrapolates from our analysis some of the ways in which script-based comparisons across country or culture can inform the more general task of making information processing-based comparisons among entrepreneurs across other contexts. [source] Alcohol drinking pattern and subjective health in a population-based studyADDICTION, Issue 9 2006Saverio Stranges ABSTRACT Aims Some patterns of alcohol consumption (e.g. binge drinking, drinking outside of meals) have been associated with detrimental effects on health outcomes. Subjective health provides a global assessment of health status and is a strong predictor of total mortality; however, little is known about its relationship with alcohol drinking pattern. The association between several drinking patterns (i.e. drinking intensity and frequency, frequency of intoxication, drinking outside of meals, and beverage type) and subjective health was examined in a random sample of 3586 women and men. Design A population-based cross-sectional study. Methods Subjective health was assessed using the physical and mental health component summaries of the Short Form-36 health survey questionnaire. Alcohol consumption refers to the 30 days before the interview. Analysis of covariance compared gender-specific mean scores across alcohol drinking patterns. Findings Overall, non-current drinkers reported poorer physical and mental health than life-time abstainers and current drinkers, while no consistent differences were found between life-time abstainers and current drinkers. In female current drinkers, daily drinking, beer and mixed beverage consumption were associated with better mental health. In male current drinkers, moderate alcohol consumption (2,2.9 drinks per day), wine and mixed beverage consumption were associated with better physical health. Intoxication and liquor consumption were associated with poorer mental health in women and poorer physical health in men. No consistent associations were found for drinking outside meals. Conclusions Aspects of drinking pattern may affect subjective health differentially in women and men. Overall, intoxication and liquor drinking are associated with poorer self-perceived health status than regular, moderate consumption of other alcoholic beverages. [source] Separable approximations of space-time covariance matricesENVIRONMETRICS, Issue 7 2007Marc G. Genton Abstract Statistical modeling of space-time data has often been based on separable covariance functions, that is, covariances that can be written as a product of a purely spatial covariance and a purely temporal covariance. The main reason is that the structure of separable covariances dramatically reduces the number of parameters in the covariance matrix and thus facilitates computational procedures for large space-time data sets. In this paper, we discuss separable approximations of nonseparable space-time covariance matrices. Specifically, we describe the nearest Kronecker product approximation, in the Frobenius norm, of a space-time covariance matrix. The algorithm is simple to implement and the solution preserves properties of the space-time covariance matrix, such as symmetry, positive definiteness, and other structures. The separable approximation allows for fast kriging of large space-time data sets. We present several illustrative examples based on an application to data of Irish wind speeds, showing that only small differences in prediction error arise while computational savings for large data sets can be obtained. Copyright © 2007 John Wiley & Sons, Ltd. [source] Temporal analysis of spatial covariance of SO2 in EuropeENVIRONMETRICS, Issue 4 2007Marco Giannitrapani Abstract In recent years, the number of applications of spatial statistics has enormously increased in environmental and ecological sciences. A typical problem is the sampling of a pollution field, with the common objective of spatial interpolation. In this paper, we present a spatial analysis across time, focusing on sulphur dioxide (SO2) concentrations monitored from 1990 to 2001 at 125 sites across Europe. Four different methods of trend estimation have been used, and comparisons among them are shown. Spherical, Exponential and Gaussian variograms have been fitted to the residuals and compared. Time series analyses of the range, sill and nugget have been undertaken and a suggestion for defining a unique spatial correlation matrix for the overall time period of analysis is proposed. Copyright © 2006 John Wiley & Sons, Ltd. [source] | ||||||||||||||||||||||||||||||||||||||||||||||