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Linear Modelling (linear + modelling)
Kinds of Linear Modelling Selected AbstractsRight wing authoritarianism, social dominance orientation and the dimensions of generalized prejudiceEUROPEAN JOURNAL OF PERSONALITY, Issue 2 2007John Duckitt Abstract Prior research suggests that individuals' prejudiced attitudes form a single generalized dimension predicted by Right Wing Authoritarianism (RWA) and Social Dominance Orientation (SDO). A dual process approach, however, expects different domains of generalized prejudice that relate differentially to RWA and SDO. To test this, 212 participants rated attitudes to 24 typically disliked groups. Factor analysis revealed three distinct generalized prejudice dimensions. Hierarchical Linear Modelling indicated that attitudes towards a ,dangerous' groups domain was significantly related only with RWA, attitudes toward a second ,derogated' groups domain was related only to SDO, and attitudes toward a third, ,dissident' groups, domain was significantly related to both, but powerfully with RWA and weakly with SDO. These findings have implications for explaining and reducing prejudice. Copyright © 2006 John Wiley & Sons, Ltd. [source] Dispersal and recruitment dynamics in the fleshy-fruited Persoonia lanceolata (Proteaceae)JOURNAL OF VEGETATION SCIENCE, Issue 6 2007Tony D. Auld Abstract Question: What is the role of dispersal, persistent soil seed banks and seedling recruitment in population persistence of fleshy-fruited obligate seeding plant species in fire-prone habitats? Location: Southeastern Australia. Methods: We used a long-term study of a shrubby, fleshy-fruited Persoonia species (Proteaceae) to examine (1) seed removal from beneath the canopy of adult plants; (2) seedling recruitment after fire; (3) the magnitude and location of the residual soil seed bank; and (4) the implications for fire management of obligate seeding species. We used demographic sampling techniques combined with Generalised Linear Modelling and regression to quantify population changes over time. Results: Most of the mature fruits (90%) on the ground below the canopy of plants were removed by Wallabia bicolor (Swamp wallaby) with 88% of seeds extracted from W. bicolor scats viable and dormant. Wallabies play an important role in moving seeds away from parent plants. Their role in occasional long distance dispersal events remains unknown. We detected almost no seed predation in situ under canopies (< 1%). Seedling recruitment was cued to fire, with post-fire seedling densities 6-7 times pre-fire adult densities. After fire, a residual soil seed bank was present, as many seeds (77-100%) remained dormant and viable at a soil depth where successful future seedling emergence is possible (0-5 cm). Seedling survival was high (> 80%) with most mortality within 2 years of emergence. Plant growth averaged 17 cm per year. The primary juvenile period of plants was 7,8 years, within the period of likely return fire intervals in the study area. We predicted that the study population increased some five-fold after the wildfire at the site. Conclusions: Residual soil seed banks are important, especially in species with long primary juvenile periods, to buffer the populations against the impact of a second fire occurring before the seed bank is replenished. [source] Variation in litter under individual tree crowns: Implications for scattered tree ecosystemsAUSTRAL ECOLOGY, Issue 1 2010CHRIS MCELHINNY Abstract In forest ecosystems litter is usually assessed in terms of the average amount produced by the canopy. In scattered tree ecosystems this approach is problematic because the canopy is discontinuous and the spatial arrangement of litter highly variable. We addressed this problem by quantifying the spatial variation in litter load and litter composition associated with individual trees in a Eucalyptus melliodora , Eucalyptus blakelyi woodland. Litter was sampled under crowns and in grassland adjacent to 10 E. blakelyi and 10 E. melliodora trees ranging in diameter at breast height (dbh) from 14 to 129 cm. A total of 302 L samples were collected from these trees, at distances ranging from 0 to 42 m from main stem. The sampled litter loads ranged from 0.02 to 109.3 t ha,1 and were significantly higher under tree crowns than in grassland for litter and each component of litter (leaves, bark, fine twigs, coarse twigs). In particular, the mean litter load under tree crowns (12.5 t ha,1) was an order of magnitude higher than the mean litter load in grassland (1.27 t ha,1). There was a significant (P = 0.0103) positive relationship between mean litter load under the tree crown and dbh, indicating larger trees produced more litter per unit area of ground than smaller trees. Generalized Linear Modelling produced highly significant (P < 0.0001) models predicting the spatial variation in litter load and litter composition in terms of distance from main stem and dbh. Our models demonstrate gradients in litter load and composition under tree crowns. These gradients were most pronounced for the large trees in our study. The disproportionate input of litter and variety of litter components associated with large trees in our study supports their keystone role in scattered tree ecosystems and highlights the need to maintain these structures in agricultural landscapes. [source] Echinococcus granulosus in northern QueenslandAUSTRALIAN VETERINARY JOURNAL, Issue 9 20061. Prevalence in cattle Objective To determine the prevalence and geographical distribution of hydatidosis and investigate factors that might be expected to influence the prevalence of hydatids in cattle in Queensland north of the Tropic of Capricorn. To determine the effect of natural levels of infection on carcase weight and subsequent economic loss. Procedure An abattoir survey conducted in 1981 provided information on the distribution, prevalence and viability of hydatid cysts in cattle from all shires north of the Tropic of Capricorn in Queensland. Livers, lungs and spleens from 10,382 cattle were palpated at abattoirs in Cairns, Townsville and Rockhampton to detect hydatid cysts. Prevalence of infection in cattle in each shire was estimated from results of the abattoir study together with reports of infection in a further 22,185 cattle obtained from abattoir records. Linear modelling was used to define the effect of geographical origin, age, breed and sex on prevalence of infection. Differences in the weights of carcases between infected and non-infected cattle of the same age, sex, breed and property of origin were examined. The economic loss to the beef industry in the region surveyed was estimated. Results Cattle infected with hydatids originated almost entirely from regions to the east of the Great Dividing Range. The mean prevalence inside this zone was 28% compared with 3% in other areas. Viable protoscoleces were found in 0.7% of cysts. Geographical origin and age of the cattle were the most significant factors influencing prevalence. Infection with hydatids had no effect on carcase weight. Economic loss was limited to that associated with condemnations of organs at meat inspection, estimated to be $0.5 million per annum in 1981 and $6 million in 2004. The distribution of hydatids in Queensland north of the Tropic of Capricorn corresponded most closely with the distribution of small wallabies such as Macropus dorsalis (black-striped wallaby), M parryi (whiptail wallaby) and M rufogriseus (red-necked wallaby). Conclusions It was concluded that cattle are not an important part of maintaining the life-cycle of E granulosus in Queensland north of the Tropic of Capricorn. Within the endemic zone, which is almost all to the east of the Great Dividing Range, the local pattern of bovine echinococcosis is most likely to be determined by the presence or absence of small species of wallaby such as M dorsalis, M parryi and M rufogriseus. [source] Bilby distribution and fire: a test of alternative models of habitat suitability in the Tanami Desert, AustraliaECOGRAPHY, Issue 6 2007Richard Southgate The distribution of the bilby Macrotis lagotis was assessed in the Tanami Desert using stratified random plots, repetitively sampled transects, aerial survey transects, and ground truth plots. Compared to a previous assessment of distribution, the extent of occurrence has changed little in the last 20 yr. However, the area of occupancy is small relative to the extent of occurrence and <25% of the current geographic range has bilby sign <20 km apart. Generalised linear modelling was used to determine the strength of association between bilby occurrence and habitat variables and identify refugia characteristics. Four competing candidate models were examined to determine whether bilby occurrence associated significantly with productive substrates and introduced herbivores, the distribution of key predator species, the pattern of fire, and climatic gradients including rainfall and temperature. For the entire study area, bilby presence associated most strongly with variables of mean annual rainfall, substrate type and the probability of dingo occurrence. Proximity to recently burnt habitat formed a significant predictor of bilby occurrence in a model derived for a reduced part of the study area where most sign was found. The work suggested that the current frameworks underpinning understanding of biotic distributions in arid Australia are deficient, and that climatic gradients, lateritic and rocky systems, and predators need to be incorporated into our thinking in the future. The extent of occurrence based on outlier records from opportunistic reports provided a misleading indication of the true status of the bilby. [source] ,I have no interest in drinking': a cross-national comparison of reasons why men and women abstain from alcohol useADDICTION, Issue 10 2009Sharon Bernards ABSTRACT Aims To examine country differences in reasons for abstaining including the association of reasons with country abstaining rate and drinking pattern. Participants Samples of men and women from eight countries participating in the GENACIS (Gender Alcohol and Culture: an International Study) project. Methods Surveys were conducted with 3338 life-time abstainers and 3105 former drinkers. Respondents selected all applicable reasons for not drinking from a provided list. Analyses included two-level hierarchical linear modelling (HLM) regression. Findings Reasons for abstaining differed significantly for life-time abstainers compared to former drinkers, by gender and age, and by country-level abstaining rate and frequency of drinking. Life-time abstainers were more likely than former drinkers to endorse ,no interest', ,religion' and ,upbringing' and more reasons overall. Gender differences, especially among former drinkers, suggested that norms restricting drinking may influence reasons that women abstain (,no interest', ,not liking taste') while drinking experiences may be more important considerations for men (,afraid of alcohol problems', ,bad effect on activities'). Younger age was associated with normative reasons (,no interest', ,taste', ,waste of money') and possibly bad experiences (,afraid of problems'). Reasons such as ,religion', ,waste of money' and ,afraid of alcohol problems' were associated with higher country-level rates of abstaining. Higher endorsement of ,drinking is bad for health' and ,taste' were associated with a country pattern of less frequent drinking while ,not liking effects' was associated with higher drinking frequency. Conclusions Reasons for abstaining depend on type of abstainer, gender, age and country drinking norms and patterns. [source] Spatial and temporal analysis of fMRI data on word and sentence readingEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 7 2007Sven Haller Abstract Written language comprehension at the word and the sentence level was analysed by the combination of spatial and temporal analysis of functional magnetic resonance imaging (fMRI). Spatial analysis was performed via general linear modelling (GLM). Concerning the temporal analysis, local differences in neurovascular coupling may confound a direct comparison of blood oxygenation level-dependent (BOLD) response estimates between regions. To avoid this problem, we parametrically varied linguistic task demands and compared only task-induced within-region BOLD response differences across areas. We reasoned that, in a hierarchical processing system, increasing task demands at lower processing levels induce delayed onset of higher-level processes in corresponding areas. The flow of activation is thus reflected in the size of task-induced delay increases. We estimated BOLD response delay and duration for each voxel and each participant by fitting a model function to the event-related average BOLD response. The GLM showed increasing activations with increasing linguistic demands dominantly in the left inferior frontal gyrus (IFG) and the left superior temporal gyrus (STG). The combination of spatial and temporal analysis allowed a functional differentiation of IFG subregions involved in written language comprehension. Ventral IFG region (BA 47) and STG subserve earlier processing stages than two dorsal IFG regions (BA 44 and 45). This is in accordance with the assumed early lexical semantic and late syntactic processing of these regions and illustrates the complementary information provided by spatial and temporal fMRI data analysis of the same data set. [source] The Social Networks of People with Intellectual Disability Living in the Community 12 Years after Resettlement from Long-Stay HospitalsJOURNAL OF APPLIED RESEARCH IN INTELLECTUAL DISABILITIES, Issue 4 2006Rachel Forrester-Jones Background, The social inclusion of people with intellectual disabilities presents a major challenge to services. As part of a 12-year follow up of people resettled from long-stay hospitals, the size of 213 individuals' social networks and the types of social support they received were investigated, as viewed by people with intellectual disabilities themselves. The types of support received in four different kinds of community accommodation were compared. Method, Individuals were interviewed and their social support networks mapped using a Social Network Guide developed for the study. Descriptive statistics were generated and comparisons made using generalized linear modelling. Results, The sample comprised 117 men (average age 51 years) and 96 women (average age 56 years). All but seven were White British, 92% were single and they had in general, mild to moderate intellectual disabilities. The average network size was 22 members (range 3,51). The mean density was 0.5. A quarter of all network members were other service users with intellectual disabilities and a further 43% were staff. Only a third of the members were unrelated to learning disability services. In general, the main providers of both emotional and practical support were staff, although these relationships were less likely to be described as reciprocal. Other people with intellectual disabilities were the second most frequent providers of all types of support. People in small group homes, hostels and supported accommodation were significantly more likely to report close and companiable relationships than those in residential and nursing homes, but they also reported a greater proportion of critical behaviour. Conclusions, The social networks revealed in this study are considerably larger than those of previous studies which have relied on staff reports, but findings about the generally limited social integration of people with intellectual disabilities are similar. A clearer policy and practice focus on the desirability of a range of different social contexts from which to derive potentially supportive network members is required so that people do not remain segregated in one area of life. [source] Membership Matters: On the Value of Being Embedded in Customer NetworksJOURNAL OF MANAGEMENT STUDIES, Issue 6 2010Øystein D. Fjeldstad abstract Learning about customers and their contexts is vital to firm strategy. We examine how firms can learn by participating in their customers' networks. Specifically, we explain how a bank can increase the value that it creates for customers by being embedded in the networks in which the customers are embedded. We argue that knowledge pertinent to a particular customer is available in the network of affiliated, inter-related customers, and that being structurally embedded in this network can help banks overcome information asymmetries. We use hierarchical linear modelling to test the argument that a bank's structural embeddedness in its customers' network positively affects the bank's ability to offer favourable credit terms. We find that not only does such structural embeddedness affect credit terms, but it also moderates the effects of previously examined relational embeddedness on credit terms. [source] Treatment of paediatric atopic dermatitis with pimecrolimus (Elidel®, SDZ ASM 981): impact on quality of life and health-related quality of lifeJOURNAL OF THE EUROPEAN ACADEMY OF DERMATOLOGY & VENEREOLOGY, Issue 3 2006SP McKenna Abstract Aim, To report on quality of life (QoL) and health-related quality of life (HRQL) impacts of pimecrolimus (Elidel®, Novartis A.G., Basel, Switzerland, SDZ ASM 981) 1% cream in the long-term treatment of paediatric atopic dermatitis. Methods, QoL and HRQL data are presented from two 12-month international clinical trials evaluating the efficacy and safety of pimecrolimus 1% cream. Both trials were randomized and double blinded and compared two treatment strategies, one involving the use of emollients, pimecrolimus and topical corticosteroids, the other is ,usual care' (emollients plus topical corticosteroids) with a vehicle cream to maintain study blinding. The first trial (the infant trial) involved patients between ages 3 months and 2 years, whereas the children trial included patients aged 2,17 years. In both trials, QoL of the affected child's parent was evaluated with the parent's index of quality of life in atopic dermatitis (PIQoL-AD). HRQL was assessed in the children trial only with the children's dermatology life quality index (CDLQI). QoL and HRQL assessments were conducted at baseline, 6 weeks, 6 months and 12 months. Results, Generalized linear modelling of PIQoL-AD scores at each post-baseline visit showed a greater impact on parent's QoL for pimecrolimus compared with control at all time-points in both trials. HRQL scores showed a greater improvement from baseline for children in the pimecrolimus group compared with those in the control group at all time-points. Conclusions,, The results show a beneficial impact of pimecrolimus on parents' QoL in paediatric atopic dermatitis, confirming findings from earlier shorter term trials. There was also a clear benefit to the HRQL of the children treated. [source] Generalized linear modelling in periglacial studies: terrain parameters and patterned groundPERMAFROST AND PERIGLACIAL PROCESSES, Issue 4 2004Miska Luoto Abstract Generalized linear models (GLM) are mathematical extensions of linear models. GLM models are more flexible and better suited for analysing relationships of spatial data, which can often be poorly represented by classical Gaussian distributions such as least-square-regression techniques. This paper demonstrates GLM model-building procedures step-by-step for the distribution and abundance of active patterned ground in northern Finland. The exercise is based on data from an area of 200,km2 (800 modelling squares of 0.25,km2). Both the distribution and abundance models clearly indicate an increasing activity of patterned ground with (1) increasing soil moisture and (2) proportion of concave topography. Activity decreases with increasing altitude. We conclude that GLM techniques combined with a geographic information system can play an important role in analysing and modelling periglacial data sets. Copyright © 2004 John Wiley & Sons, Ltd. [source] Coordinated regulation of maize genes during increasing exposure to ultraviolet radiation: identification of ultraviolet-responsive genes, functional processes and associated potential promoter motifsPLANT BIOTECHNOLOGY JOURNAL, Issue 6 2007Carletha R. Blanding Summary Genetic gain in the yield of modern maize reflects increased stress tolerance. The manipulation of genes for deliberate alterations in tolerance relies on an understanding of the regulation and components of stress responses. Transcriptome analysis of an ultraviolet (UV) radiation time course with paired treatment and control measurements yielded groups of coordinately regulated genes and gene ontology processes. A comparison of the patterns of gene expression with patterns of morphological changes allowed the identification of physiologically relevant gene expression regulons. A set of genes significantly affected by UV radiation in maize leaves was selected by linear modelling plus order-restricted inference profile matches. This gene list was used to find upstream sequence motifs that predict the UV regulation of maize gene expression. [source] Curve registration by local regressionTHE CANADIAN JOURNAL OF STATISTICS, Issue 1 2000A. Kneip Abstract Functional data analysis involves the extension of familiar statistical procedures such as principal-components analysis, linear modelling and canonical correlation analysis to data where the raw observation is a function x, (t). An essential preliminary to a functional data analysis is often the registration or alignment of salient curve features by suitable monotone transformations hi(t). In effect, this conceptualizes variation among functions as being composed of two aspects: phase and amplitude. Registration aims to remove phase variation as a preliminary to statistical analyses of amplitude variation. A local nonlinear regression technique is described for identifying the smooth monotone transformations hi, and is illustrated by analyses of simulated and actual data. L'analyse de données se présentant sous la forme de fonctions x,(t) repose sur la généralisation d'outils statistiques familiers tels que l'analyse en composantes principales, les modèles linéaires et l'analyse des corrélations canoniques. L'étalonnage des caractéristiques saillantes des courbes à l'aide de transformations monotones hi(t) constitue souvent un préiequis essentiel au traitement statistique de telles données. II découle d'une décomposition en deux parties de la variation entre les fonctions observées: une phase et une amplitude. L'étalonnage vise à éliminer la première de ces deux sources de variation, ce qui permet de concentrer ensuite l'analyse sur la seconde. Les auteurs décrivent ici une technique de régression non linéaire locale facilitant l'identification de transformations monotones lisses hi appropriées. Leur propos est illustré à l'aide de données réelles et simulées. [source] Does a top-predator provide an endangered rodent with refuge from an invasive mesopredator?ANIMAL CONSERVATION, Issue 4 2009M. Letnic Abstract In arid environments, ecological refuges are often conceptualised as places where animal species can persist through drought owing to the localised persistence of moisture and nutrients. The mesopredator release hypothesis (MRH) predicts that reduced abundance of top-order predators results in an increase in the abundance of smaller predators (mesopredators) and consequently has detrimental impacts on the prey of the smaller predators. Thus according to the MRH, the existence of larger predators may provide prey with refuge from predation. In this study, we investigated how the abundance of an endangered rodent Notomys fuscus is affected by Australia's largest predator, the dingo Canis lupus dingo, introduced mesopredators, introduced herbivores, kangaroos and rainfall. Our surveys showed that N. fuscus was more abundant where dingoes occurred. Generalised linear modelling showed that N. fuscus abundance was associated positively with dingo activity and long-term annual rainfall and negatively with red fox Vulpes vulpes activity. Our results were consistent with the hypothesis that areas with higher rainfall and dingoes provide N. fuscus with refuge from drought and predation by invasive red foxes, respectively. Top-order predators, such as dingoes, could have an important functional role in broad-scale biodiversity conservation programmes by reducing the impacts of mesopredators. [source] Developing a modern pollen,climate calibration data set for NorwayBOREAS, Issue 4 2010ANNE E. BJUNE Bjune, A. E., Birks, H. J. B., Peglar, S. M. & Odland, A. 2010: Developing a modern pollen,climate calibration data set for Norway. Boreas, Vol. 39, pp. 674,688. 10.1111/j.1502-3885.2010.00158.x. ISSN 0300-9483. Modern pollen,climate data sets consisting of modern pollen assemblages and modern climate data (mean July temperature and mean annual precipitation) have been developed for Norway based on 191 lakes and 321 lakes. The original 191-lake data set was designed to optimize the distribution of the lakes sampled along the mean July temperature gradient, thereby fulfilling one of the most critical assumptions of weighted-averaging regression and calibration and its relative, weighted-averaging partial least-squares regression. A further 130 surface samples of comparable taphonomy, taxonomic detail and analyst became available as a result of other projects. These 130 samples, all from new lakes, were added to the 191-lake data set to create the 321-lake data set. The collection and construction of these data sets are outlined. Numerical analyses involving generalized linear modelling, constrained ordination techniques, weighted-averaging partial least-squares regression, and two different cross-validation procedures are used to asses the effects of increasing the size of the calibration data set from 191 to 321 lakes. The two data sets are used to reconstruct mean July temperature and mean annual precipitation for a Holocene site in northwest Norway and a Lateglacial site in west-central Norway. Overall, little is to be gained by increasing the modern data set beyond about 200 lakes in terms of modern model performance statistics, but the down-core reconstructions show less between-sample variability and are thus potentially more plausible and realistic when based on the 321-lake data set. [source] | ||||||||||||||||