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General Linear Models (general + linear_models)
Selected AbstractsExploratory Analysis of Cerebral Oxygen Reserves During Sleep Onset in Older and Younger AdultsJOURNAL OF AMERICAN GERIATRICS SOCIETY, Issue 5 2008Barbara W. Carlson RN OBJECTIVES: To explore differences in cerebral oxygen reserves during sleep in old and young adults. DESIGN: Descriptive cross-sectional study. SETTING: General clinical research center. PARTICIPANTS: Nine old (aged 65,84) and 10 young (aged 21,39) adults. MEASUREMENTS: Subjects were monitored during the first nightly sleep cycle using standard polysomnography, including measures of arterial oxyhemoglobin saturation (SaO2). Changes in regional cerebral oxyhemoglobin saturation (rcSO2) were used to estimate cerebral oxygen reserves. General linear models were used to test group differences in the change in SaO2 and rcSO2 during sleep. RESULTS: Older subjects had lower SaO2 than young subjects before sleep (baseline) (F(1,18)=5.1, P=.04) and during sleep (F(1,18)=10.7, P=.01). During sleep, half of the older subjects and none of the younger ones had SaO2 values below 95%. In addition, the older subjects had more periods of oxygen desaturation (drops in SaO2,4%) (chi-square=24.3, P=.01) and lower SaO2 levels during desaturation (F(1,18)=11.1, P<.01). Although baseline values were similar, rcSO2 decreased during sleep 2.1% in older subjects (F(1,8)=3.8, P=.05) but increased 2.1% during sleep in younger subjects (F(1,9)=4.6, P=.04). When the older subjects awakened from sleep, rcSO2, but not SaO2, returned to baseline; both returned to baseline in younger subjects. CONCLUSION: This exploratory analysis generated the hypothesis that lower SaO2, combined with declines in regional blood flow, contributes to decline in cerebral oxygen reserves during sleep in older subjects. Further study will assess the effects of factors (e.g., medical conditions, subclinical disorders, and sleep architecture) that might account for these differences. [source] Comparative dynamics of avian communities across edges and interiors of North American ecoregionsJOURNAL OF BIOGEOGRAPHY, Issue 4 2006Krithi K. Karanth Abstract Aim, Based on a priori hypotheses, we developed predictions about how avian communities might differ at the edges vs. interiors of ecoregions. Specifically, we predicted lower species richness and greater local turnover and extinction probabilities for regional edges. We tested these predictions using North American Breeding Bird Survey (BBS) data across nine ecoregions over a 20-year time period. Location, Data from 2238 BBS routes within nine ecoregions of the United States were used. Methods, The estimation methods used accounted for species detection probabilities < 1. Parameter estimates for species richness, local turnover and extinction probabilities were obtained using the program COMDYN. We examined the difference in community-level parameters estimated from within exterior edges (the habitat interface between ecoregions), interior edges (the habitat interface between two bird conservation regions within the same ecoregion) and interior (habitat excluding interfaces). General linear models were constructed to examine sources of variation in community parameters for five ecoregions (containing all three habitat types) and all nine ecoregions (containing two habitat types). Results, Analyses provided evidence that interior habitats and interior edges had on average higher bird species richness than exterior edges, providing some evidence of reduced species richness near habitat edges. Lower average extinction probabilities and turnover rates in interior habitats (five-region analysis) provided some support for our predictions about these quantities. However, analyses directed at all three response variables, i.e. species richness, local turnover, and local extinction probability, provided evidence of an interaction between habitat and region, indicating that the relationships did not hold in all regions. Main conclusions, The overall predictions of lower species richness, higher local turnover and extinction probabilities in regional edge habitats, as opposed to interior habitats, were generally supported. However, these predicted tendencies did not hold in all regions. [source] Evaluation of platelet activation in canine immune-mediated haemolytic anaemiaJOURNAL OF SMALL ANIMAL PRACTICE, Issue 6 2010A. E. Ridyard Objectives: To establish whether heightened platelet activation is a common feature of canine immune-mediated haemolytic anaemia, and to evaluate the hypothesis that platelet activation plays a role in the pathogenesis of thromboembolism. Methods: Using whole-blood flow-cytometric analysis, the proportion of activated platelets and platelet-leucocyte aggregates in blood samples from 14 dogs with immune-mediated haemolytic anaemia and 14 healthy dogs was calculated. General linear models with binomial errors were used to compare groups. Results from the immune-mediated haemolytic anaemia-affected dogs were then correlated with established risk factors for thromboembolism in canine immune-mediated haemolytic anaemia, D-dimer concentration and antithrombin activity. Results: There was a strong correlation between platelet activation and severe thrombocytopenia, with heightened platelet activation being observed predominantly in severely thrombocytopenic dogs. Clinical Significance: Dogs with immune-mediated haemolytic anaemia, particularly those with concurrent severe thrombocytopenia, are likely to have heightened platelet activation, which may play a role in the pathogenesis of thromboembolism. [source] The responsiveness of the OAB-q among OAB patient subgroups,NEUROUROLOGY AND URODYNAMICS, Issue 2 2007Karin S. Coyne Abstract Aims Although the majority of patients with overactive bladder (OAB) are continent, most patient-reported outcome measures for OAB were designed for patients with urinary incontinence. The overactive bladder questionnaire (OAB-q) was developed to assess symptom bother and HRQL among both continent and incontinent OAB patients; however, the responsiveness of the OAB-q among continent patients has not been evaluated. The purpose of this analysis was to assess the responsiveness of the OAB-q among OAB patient subgroups with a focus on continent patients. Methods Post-hoc analyses were conducted from two 12-week trials of tolterodine for the treatment of OAB. Patients completed the OAB-q and daily bladder diaries (assessing frequency, urgency, and incontinence episodes) at baseline, 4 weeks, and 12 weeks. Three patient subgroups were identified on the basis of continence status at all three timepoints: (1) continent; (2) incontinent; and (3) incontinent at baseline and continent by Week 12 (ITC). General linear models were used to compare changes from baseline, and Spearman correlations assessed the association between OAB-q changes and bladder diary changes. Effect sizes were computed separately for each group. Results A total of 262 continent, 552 incontinent, and 397 ITC patients were included in this analysis. Continent patients tended to be younger than incontinent patients, and patients were predominantly female, although continent patients had the highest percentage of male patients in both studies. Compared with continent patients, patients who were incontinent at baseline tended to have greater symptom bother and lower HRQL at baseline. All OAB-q change scores were consistently greatest for the ITC group (12.1,33.9), and greater for continent patients (10.8,28.6) than for incontinent patients (7.6,20.1). All three groups of patients experienced reductions in frequency and urgency episodes, and these changes were significantly correlated with changes in the OAB-q scales. Among all three groups, effect sizes were in the moderate-to-large range for all OAB-q subscales except Social Interaction. Conclusions The OAB-q is highly responsive to change between continent and incontinent patients with OAB, and is a valid tool for measuring treatment outcomes among continent OAB patients. Neurourol. Urodynam. 26:196,203, 2007. © 2006 Wiley-Liss, Inc. [source] The importance of ingestion rates for estimating food quality and energy intakeAMERICAN JOURNAL OF PRIMATOLOGY, Issue 10 2006Oliver Schülke Abstract Testing ecological or socioecological models in primatology often requires estimates of individual energy intake. It is a well established fact that the nutrient content (and hence the energy content) of primate food items is highly variable. The second variable in determining primate energy intake, i.e., the ingestion rate, has often been ignored, and few studies have attempted to estimate the relative importance of the two predictors. In the present study individual ingestion rates were measured in two ecologically very different populations of Hanuman langurs (Semnopithecus entellus) at Jodhpur, India, and Ramnagar, Nepal. Protein and soluble sugar concentrations in 50 and 100 food items. respectively, were measured using standardized methods. Variation in ingestion rates (gram of dry matter per minute) was markedly greater among food items than among langur individuals in both populations, but did not differ systematically among food item categories defined according to plant part and age. General linear models (GLMs) with ingestion rate, protein, and soluble sugar content explained 40,80% of the variation in energy intake rates (kJ/min). The relative importance of ingestion rates was either similar (Ramnagar) or much greater (Jodhpur) than the role of sugar and/or protein content in determining the energy intake rates of different items. These results may impact socioecological studies of variation in individual energy budgets, investigations of food choice in relation to chemical composition or sensory characteristics, and research into habitat preferences that measures habitat quality in terms of abundance of important food sources. We suggest a definition of food quality that includes not only the amount of valuable food contents (energy, vitamins, and minerals) and the digestibility of different foods, but also the rate at which the food can be harvested and processed. Such an extended definition seems necessary because time may constrain primates when feeding competition is intense and foraging is risk-prone. Am. J. Primatol. 68:951,965, 2006. © 2006 Wiley-Liss, Inc. [source] Effects of forest management on epiphytic lichen diversity in Mediterranean forestsAPPLIED VEGETATION SCIENCE, Issue 2 2010Gregorio Aragón Abstract Question: What are the responses of epiphytic lichens to the intensity of management along a large environmental gradient in Mediterranean Quercus forests? Location: Central Spain. Methods: This study was carried out on 4590 trees located in 306 forest stands dominated by Quercus faginea or Quercus ilex ssp. ballota. The effect of forest management and other predictor variables on several species diversity indicators were studied. Variables modelled were total species richness, cyanolichen richness and community composition. A large number of predictor variables were included: forest fragmentation (patch size, stand variability), climate and topographic (altitude, slope, sun radiation, annual rainfall and mean annual temperature) and intensity of management. General linear models and constrained ordination techniques were used to model community traits and species composition, respectively. Results: Total richness and especially cyanolichens richness were significantly and negatively affected by the intensity of management. Lichen composition was influenced by management intensity, climatic and topographic variables and stand variability. Conclusions: In Mediterranean forests, human activities related to forestry, agricultural and livestock use cause impoverishment of lichen communities, including the local disappearance of the most demanding species. The conservation of unmanaged forests with a dense canopy is crucial for lichen diversity. [source] Sublethal effects of methylmercury on fecal metabolites of testosterone, estradiol, and corticosterone in captive juvenile white ibises (Eudocimus albus),ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 5 2009Evan M. Adams Abstract Methylmercury (MeHg) is a globally distributed neurotoxin, endocrine disruptor, and teratogen, and its effects on birds are poorly understood, especially within an environmentally relevant exposure range. In an effort to understand the potential causal relationship between MeHg exposure and endocrine development, we established four dietary exposure groups (0 [control], 0.05, 0.1, and 0.3 mg/kg wet wt/d of MeHg) of postfledging white ibises (Eudocimus albus) in a divided, free-flight aviary that spanned the estimated range of environmental exposure for this species. Fecal samples were collected from individually identified ibises over six months in 2005 and processed for hormone evaluation. Significant sex-related differences in fecal estradiol concentrations, though unpredicted in direction, suggest that this steroid could be related to juvenile development in this species. Using repeated-measures general linear models, we tested a set of candidate models to explain variation in endocrine expression. We found that MeHg exposure led to significant differences in fecal estradiol concentrations between the control and medium-dose groups, whereas differences in fecal corticosterone concentrations were observed between the control and both the low- and high-dose groups. These results suggest highly nonlinear dose-response patterns for MeHg. Many endocrine-disrupting contaminants are theorized to affect multiple endpoints in a nonlinear manner, making results difficult to interpret using a traditional toxicological approach. The evidence presented here suggests that endocrine effects of MeHg exposure could behave similarly. [source] Predictors and correlates of edentulism in the healthy old people in Edinburgh (HOPE) studyGERODONTOLOGY, Issue 4 2008John M. Starr Objectives:, To determine the extent to which correlates of edentulism are explained by an association between tooth loss and cognitive ability. Methods:, Participants in the Healthy Old People in Edinburgh (HOPE) study aged 70 or more at baseline were assessed and health, cognitive, socio-economic and socio-environmental data collected on four consecutive occasions. It was noted whether the participant had any retained teeth and if not, the age when the last tooth was lost. Prior determinants of edentulism were investigated with binary logistic regression models. At the 9-year follow-up, associations with edentulism were examined using general linear models with edentulism as an independent factor. Results:, 201 participants were adequately tested, of whom 104 (51.7%) were edentulous. A logistic regression model that considered age, sex, education, social class, deprivation index of residence, objective distance from dentist, participant's estimate of distance from dentist and NART-estimated IQ (NARTIQ) found age (p = 0.032), occupational class (p = 0.019) and NARTIQ (p = 0.027) as significant predictors of edentulism. Cox's proportional hazards modelling found only NARTIQ (p = 0.050) to be correlated. Being edentulous was associated with poorer respiratory function but not hand grip strength (p = 0.23). Edentulous participants had lower self esteem scores (p = 0.020) and poorer dietary assessment scores (p = 0.028). Being edentulous was also associated with significantly lower mean scores on all cognitive testing, although these associations became non-significant after adjustment for NARTIQ and age. Conclusions:, In healthy older people, edentulism is associated with relative impairment of cognitive ability, although this association is explained by the fact that lower original intelligence predisposes to edentulism and poorer performance on cognitive tests in old age. Once original intelligence is adjusted for, tooth loss is not related to cognitive ability. Tooth loss is, however, associated with poorer status across a wide range of health measures: physical health, nutrition, disability and self-esteem. Establishing the degree to which these health outcomes are causally related to edentulism could usefully be factored into cost,benefit analyses of programmes designed to prevent tooth loss. [source] Will northern fish populations be in hot water because of climate change?GLOBAL CHANGE BIOLOGY, Issue 10 2007SAPNA SHARMA Abstract Predicted increases in water temperature in response to climate change will have large implications for aquatic ecosystems, such as altering thermal habitat and potential range expansion of fish species. Warmwater fish species, such as smallmouth bass, Micropterus dolomieu, may have access to additional favourable thermal habitat under increased surface-water temperatures, thereby shifting the northern limit of the distribution of the species further north in Canada and potentially negatively impacting native fish communities. We assembled a database of summer surface-water temperatures for over 13 000 lakes across Canada. The database consists of lakes with a variety of physical, chemical and biological properties. We used general linear models to develop a nation-wide maximum lake surface-water temperature model. The model was extended to predict surface-water temperatures suitable to smallmouth bass and under climate-change scenarios. Air temperature, latitude, longitude and sampling time were good predictors of present-day maximum surface-water temperature. We predicted lake surface-water temperatures for July 2100 using three climate-change scenarios. Water temperatures were predicted to increase by as much as 18 °C by 2100, with the greatest increase in northern Canada. Lakes with maximum surface-water temperatures suitable for smallmouth bass populations were spatially identified. Under several climate-change scenarios, we were able to identify lakes that will contain suitable thermal habitat and, therefore, are vulnerable to invasion by smallmouth bass in 2100. This included lakes in the Arctic that were predicted to have suitable thermal habitat by 2100. [source] Bayesian comparison of spatially regularised general linear modelsHUMAN BRAIN MAPPING, Issue 4 2007Will Penny Abstract In previous work (Penny et al., [2005]: Neuroimage 24:350,362) we have developed a spatially regularised General Linear Model for the analysis of functional magnetic resonance imaging data that allows for the characterisation of regionally specific effects using Posterior Probability Maps (PPMs). In this paper we show how it also provides an approximation to the model evidence. This is important as it is the basis of Bayesian model comparison and provides a unified framework for Bayesian Analysis of Variance, Cluster of Interest analyses and the principled selection of signal and noise models. We also provide extensions that implement spatial and anatomical regularisation of noise process parameters. Hum Brain Mapp 2007. © 2006 Wiley-Liss, Inc. [source] H-methods in applied sciencesJOURNAL OF CHEMOMETRICS, Issue 3-4 2008Agnar Höskuldsson Abstract The author has developed a framework for mathematical modelling within applied sciences. It is characteristic for data from ,nature and industry' that they have reduced rank for inference. It means that full rank solutions normally do not give satisfactory solutions. The basic idea of H-methods is to build up the mathematical model in steps by using weighing schemes. Each weighing scheme produces a score and/or a loading vector that are expected to perform a certain task. Optimisation procedures are used to obtain ,the best' solution at each step. At each step, the optimisation is concerned with finding a balance between the estimation task and the prediction task. The name H-methods has been chosen because of close analogy with the Heisenberg uncertainty inequality. A similar situation is present in modelling data. The mathematical modelling stops, when the prediction aspect of the model cannot be improved. H-methods have been applied to wide range of fields within applied sciences. In each case, the H-methods provide with superior solutions compared to the traditional ones. A background for the H-methods is presented. The H-principle of mathematical modelling is explained. It is shown how the principle leads to well-defined optimisation procedures. This is illustrated in the case of linear regression. The H-methods have been applied in different areas: general linear models, nonlinear models, multi-block methods, path modelling, multi-way data analysis, growth models, dynamic models and pattern recognition. Copyright © 2008 John Wiley & Sons, Ltd. [source] Changes in gingival crevicular fluid inflammatory mediator levels during the induction and resolution of experimental gingivitis in humansJOURNAL OF CLINICAL PERIODONTOLOGY, Issue 4 2010Steven Offenbacher Offenbacher S, Barros S, Mendoza L, Mauriello S, Preisser J, Moss K, de Jager M, Aspiras M. Changes in gingival crevicular fluid inflammatory mediator levels during the induction and resolution of experimental gingivitis in humans. J Clin Periodontol 2010; 37: 324,333. doi: 10.1111/j.1600-051X.2010.01543.x Abstract Aim: The goal of this study is to characterize the changes in 33 biomarkers within the gingival crevicular fluid during the 3-week induction and 4-week resolution of stent-induced, biofilm overgrowth mediated, experimental gingivitis in humans. Methods: Experimental gingivitis was induced in 25 subjects for 21 days followed by treatment with a sonic powered toothbrush for 28 days. Clinical indices and gingival crevicular fluids were collected weekly during induction and biweekly during resolution. Samples were analysed using a bead-based multiplexing analysis for the simultaneous measurements of 33 biomarkers within each sample including cytokines, matrix-metalloproteinases (MMPs) and adipokines. Prostaglandin-E2 was measured by enzyme-linked immunoadsorbant assay. Statistical testing using general linear models with structured covariance matrices were performed to compare stent to contralateral (non-stent) changes in clinical signs and in biomarker levels over time. Results: Gingivitis induction was associated with a significant 2.6-fold increase in interleukin 1- , (IL- ,), a 3.1-fold increase in IL-1, and a significant decrease in multiple chemokines as well as MMPs-1, -3 and 13. All changes in clinical signs and mediators rebounded to baseline in response to treatment in the resolution phase. Conclusions: Stent-induced gingivitis is associated with marked, but reversible increases in IL- ,a and IL-1, with suppression of multiple chemokines as well as selected MMPs. [source] A FIELD-BASED METHOD FOR ESTIMATING AGE IN FREE-RANGING STELLER SEA LIONS (EUMETOPIAS JUBATUS) LESS THAN TWENTY-FOUR MONTHS OF AGEMARINE MAMMAL SCIENCE, Issue 2 2007James C. King Abstract Studies of health, survival, and development of juvenile Alaskan Steller sea lions (Eumetopias jubatus, SSL) require accurate estimates of age for wild-captured animals. However, the value and accuracy of several potential predictors of age have not been assessed with data from known-age free-ranging animals. During 2001,2005, forty-six individual SSL originally branded or tagged at ,6 mo of age were recaptured by the Alaska Department of Fish and Game (ADF&G). Using a series of general linear models, we evaluated the ability of morphometrics measurements: permanent canine tooth length (CTL), diastema (DIAS), whisker length (WHIS), and dorsal standard length (DSL) to predict the age of forty-six known-age juveniles (n= 46 ,23 mo of age). Permanent CTL was the strongest individual predictor (r2= 0.80); followed by DSL, DIAS, and WHIS (r2= 0.70, 0.56, and 0.45, respectively). The inclusion of a single sample from a 44-mo-old sea lion suggested quadratic relationships between age and all predictors for older animals. Only models including CTL predicted age to within 6 mo of known age. The equation Age = (,3.0112 +[0.6726 * CTL]+[0.4965 * DIAS]) allows for accurate age estimates of SSL ,23 mo for both sexes. [source] Management history and climate as key factors driving natterjack toad population trends in BritainANIMAL CONSERVATION, Issue 5 2010A. L. McGrath Abstract Along with other amphibian populations in Europe and elsewhere, natterjack toad Bufo calamita populations in Britain have declined since at least 1960. Conservation management since the 1970s has aimed to halt the decline and maintain viable populations at key sites throughout the species' recent historical range. Here, we assess population trends from 1985 to 2006 at 20 British B. calamita sites and evaluate the role of active management in maintaining good conservation status. We investigated the effects of 25 climatic, site-characteristic and conservation management variables on population trends using general linear models. In single-variable analyses, rainfall variables showed negative relationships with population trends. Among the site characteristics, being located at the very edge of the species' range (northern Irish Sea coast) and occurrence of common toad (B. bufo) were negatively related to B. calamita population trends. Management history (populations established via translocation as opposed to native populations) had a significant positive effect; as had sites that received greater translocation releases, undergone Species Recovery Programme management, and where common toad was absent. In multiple-variable analyses, the combined effects of management history and average pre-breeding season rainfall accounted for inter-site variation in population trends. The rainfall effects in single- and multiple-variable analyses were strongly influenced by three sites with very high rainfall whilst no clear effect was apparent for the remaining sites. This study highlights the role of climatic factors in population decline, and the importance of conservation management in stabilizing population trends. Climate change over the next 50,100 years is predicted to have limited impacts on most B. calamita populations in Britain, but strongly positive impacts on the most threatened populations located at the very edge of species' range that will benefit from reduced precipitation. A need for active conservation management will remain for the foreseeable future. [source] | |||||||||||||