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Sampling Design (sampling + design)
Kinds of Sampling Design Selected AbstractsA NOTE ON SAMPLING DESIGNS FOR RANDOM PROCESSES WITH NO QUADRATIC MEAN DERIVATIVEAUSTRALIAN & NEW ZEALAND JOURNAL OF STATISTICS, Issue 3 2006Bhramar Mukherjee Summary Several authors have previously discussed the problem of obtaining asymptotically optimal design sequences for estimating the path of a stochastic process using intricate analytical techniques. In this note, an alternative treatment is provided for obtaining asymptotically optimal sampling designs for estimating the path of a second order stochastic process with known covariance function. A simple estimator is proposed which is asymptotically equivalent to the full-fledged best linear unbiased estimator and the entire asymptotics are carried out through studying this estimator. The current approach lends an intuitive statistical perspective to the entire estimation problem. [source] Multi-scale sampling and statistical linear estimators to assess land use status and changeAPPLIED VEGETATION SCIENCE, Issue 2 2009D. Rocchini Abstract Question: Multi-temporal analysis of remotely sensed imagery has proven to be a powerful tool for assessment and monitoring of landscape diversity. Here the feasibility of assessing land-use diversity and land-use change was tested at multiple scales and over time by means of statistical linear estimators based on a probabilistic sampling design. Location: The study area (the district of Asciano, Tuscany, Italy) is characterized by erosional forms typical of Pliocene claystone (i.e. calanchi and biancane) that have been subject to the phenomenon of biancane reworking over the past 50 years, mainly owing to the expansion of intensive agriculture. Methods: Cells at two different scales (50 m × 50 m and 10 m × 10 m) were classified by two operators according to a multilevel legend, using 1954 and 2000 aerial photographs. Inter-operator agreement and accuracy were tested by Cohen's K coefficient. Total land cover estimation for each class was carried out using a multistage estimator, while the variance was estimated by means of the Wolter estimator. Field-based information on plant species composition was recorded in order to test for a relationship between land use and plant community composition by anova and indicator species analysis. Results: Agreement between photointerpreters and accuracy were significantly higher than those expected by chance, proving that the approach proposed is reproducible, as long as proper quality assurance methods are used. Our data show that, at the two scales considered (50 m × 50 m and 10 m × 10 m), crops have increased against woodlands and semi-natural areas, the latter showing the highest and significantly different mean species richness. Meanwhile, an increase in the coverage of trees and shrubs was found within the semi-natural areas, probably as a result of secondary succession occurring on typical landscape elements such as biancane. Conclusions: Inferential statistics made it possible to acquire quantitative information on the abundance of land cover classes, allowing formal multi-temporal and multi-scale analysis. Sampling design-based statistical linear estimators were found to be a powerful tool for assessing landscape trends considering both time expenditure and other costs. They make it possible to maintain the same scale of analysis over time series data and to detect both coarse- and fine-grained changes in spatial patterns. [source] Sampling designs of insect time series data: are they all irregularly spaced?OIKOS, Issue 1 2009D. V. Beresford Time series data are commonly obtained by trapping over a standardized period of time, for example daily or weekly. In this paper we present evidence that such sampling designs are inherently irregularly spaced due to the varying developmental rates and population parameters caused by changing temperatures during a sampling season. We modeled an exponentially growing population based on stable fly population growth rates, and then compare different sampling regimes to determine which produces the best estimate of population growth rate. These results are then compared to field data based on weekly sampling at three dairy farms in Ontario over two summers. Transforming catch numbers (N) to ln(N)/(number of degree days within the sampling period) corrects for the irregular spaced sampling in these data. These results support the use of measuring population parameters such as population growth rates in terms of degree days. [source] Effects of species and habitat positional errors on the performance and interpretation of species distribution modelsDIVERSITY AND DISTRIBUTIONS, Issue 4 2009Patrick E. Osborne Abstract Aim, A key assumption in species distribution modelling is that both species and environmental data layers contain no positional errors, yet this will rarely be true. This study assesses the effect of introduced positional errors on the performance and interpretation of species distribution models. Location, Baixo Alentejo region of Portugal. Methods, Data on steppe bird occurrence were collected using a random stratified sampling design on a 1-km2 pixel grid. Environmental data were sourced from satellite imagery and digital maps. Error was deliberately introduced into the species data as shifts in a random direction of 0,1, 2,3, 4,5 and 0,5 pixels. Whole habitat layers were shifted by 1 pixel to cause mis-registration, and the cumulative effect of one to three shifted layers investigated. Distribution models were built for three species using three algorithms with three replicates. Test models were compared with controls without errors. Results, Positional errors in the species data led to a drop in model performance (larger errors having larger effects , typically up to 10% drop in area under the curve on average), although not enough for models to be rejected. Model interpretation was more severely affected with inconsistencies in the contributing variables. Errors in the habitat layers had similar although lesser effects. Main conclusions, Models with species positional errors are hard to detect, often statistically good, ecologically plausible and useful for prediction, but interpreting them is dangerous. Mis-registered habitat layers produce smaller effects probably because shifting entire layers does not break down the correlation structure to the same extent as random shifts in individual species observations. Spatial autocorrelation in the habitat layers may protect against species positional errors to some extent but the relationship is complex and requires further work. The key recommendation must be that positional errors should be minimised through careful field design and data processing. [source] Rapid plant diversity assessment using a pixel nested plot design: A case study in Beaver Meadows, Rocky Mountain National Park, Colorado, USADIVERSITY AND DISTRIBUTIONS, Issue 4 2007Mohammed A. Kalkhan ABSTRACT Geospatial statistical modelling and thematic maps have recently emerged as effective tools for the management of natural areas at the landscape scale. Traditional methods for the collection of field data pertaining to questions of landscape were developed without consideration for the parameters of these applications. We introduce an alternative field sampling design based on smaller unbiased random plot and subplot locations called the pixel nested plot (PNP). We demonstrate the applicability of the PNP design of 15 m × 15 m to assess patterns of plant diversity and species richness across the landscape at Rocky Mountain National Park (RMNP), Colorado, USA in a time (cost)-efficient manner for field data collection. Our results produced comparable results to a previous study in the Beaver Meadow study (BMS) area within RMNP, where there was a demonstrated focus of plant diversity. Our study used the smaller PNP sampling design for field data collection which could be linked to geospatial information data and could be used for landscape-scale analyses and assessment applications. In 2003, we established 61 PNP in the eastern region of RMNP. We present a comparison between this approach using a sub-sample of 19 PNP from this data set and 20 of Modified Whittaker nested plots (MWNP) of 20 m × 50 m that were collected in the BMS area. The PNP captured 266 unique plant species while the MWNP captured 275 unique species. Based on a comparison of PNP and MWNP in the Beaver Meadows area, RMNP, the PNP required less time and area sampled to achieve a similar number of species sampled. Using the PNP approach for data collection can facilitate the ecological monitoring of these vulnerable areas at the landscape scale in a time- and therefore cost-effective manner. [source] Evaluating reserves for species richness and representation in northern CaliforniaDIVERSITY AND DISTRIBUTIONS, Issue 4 2006Jeffrey R. Dunk ABSTRACT The Klamath-Siskiyou forests of northern California and southern Oregon are recognized as an area of globally outstanding biological distinctiveness. When evaluated at a national or global level, this region is often, necessarily, considered to be uniformly diverse. Due to large variation in biotic and abiotic variables throughout this region, however, it is unlikely that biological diversity is uniformly distributed. Furthermore, land management decisions nearly always occur at spatial scales smaller than this entire region. Therefore, we used field data from a random sampling design to map the distribution of local and regional richness of terrestrial molluscs and salamanders within northern California's portion of the Klamath-Siskiyou region. We also evaluated the protection afforded by reserves established for varying reasons (e.g. for inspiration and recreation for people vs. species conservation) to hotspots of species richness and species representation of these taxa. No existing reserves were created with these taxa in mind, yet it was assumed that reserves established largely around considerations for the northern spotted owl (Strix occidentalis caurina) would afford adequate protection for many lesser-known species. Species of terrestrial molluscs and salamanders share two general features: (1) they have extremely low vagility, and (2) they are often associated with moist, cool microclimates. Existing reserves disproportionately included areas of hotspots of species richness for both taxa, when hotspots included the richest c. 25% of the area, whereas non-reserved lands contained greater than expected areas with lower species richness. However, when a more strict definition of hotspot was used (i.e. the richest c.10% of areas), local hotspots for both taxa were not disproportionately found in reserves. Reserves set aside largely for human aesthetics and recreation and those set aside for biodiversity both contributed to the protection of areas with high (greatest 25%) species richness. Existing biodiversity reserves represented 68% of mollusc species and 73% of salamander species, corresponding to the 99th and 93rd percentiles, respectively, of species representation achieved by simulating a random distribution of the same total area of reservation. Cumulatively, however, reserves set aside for inspiration and biodiversity represented 83% of mollusc species and 91% of salamander species. The existing reserves provide conservation value for terrestrial molluscs and salamanders. This reserve network, however, should not be considered optimal for either taxa. [source] Plant species richness and environmental heterogeneity in a mountain landscape: effects of variability and spatial configurationECOGRAPHY, Issue 4 2006Alexia Dufour The loss of biodiversity has become a matter of urgent concern and a better understanding of local drivers is crucial for conservation. Although environmental heterogeneity is recognized as an important determinant of biodiversity, this has rarely been tested using field data at management scale. We propose and provide evidence for the simple hypothesis that local species diversity is related to spatial environmental heterogeneity. Species partition the environment into habitats. Biodiversity is therefore expected to be influenced by two aspects of spatial heterogeneity: 1) the variability of environmental conditions, which will affect the number of types of habitat, and 2) the spatial configuration of habitats, which will affect the rates of ecological processes, such as dispersal or competition. Earlier, simulation experiments predicted that both aspects of heterogeneity will influence plant species richness at a particular site. For the first time, these predictions were tested for plant communities using field data, which we collected in a wooded pasture in the Swiss Jura mountains using a four-level hierarchical sampling design. Richness generally increased with increasing environmental variability and "roughness" (i.e. decreasing spatial aggregation). Effects occurred at all scales, but the nature of the effect changed with scale, suggesting a change in the underlying mechanisms, which will need to be taken into account if scaling up to larger landscapes. Although we found significant effects of environmental heterogeneity, other factors such as history could also be important determinants. If a relationship between environmental heterogeneity and species richness can be shown to be general, recently available high-resolution environmental data can be used to complement the assessment of patterns of local richness and improve the prediction of the effects of land use change based on mean site conditions or land use history. [source] Scale dependence of diversity measures in a leaf-litter ant assemblageECOGRAPHY, Issue 2 2004Maurice Leponce A reliable characterization of community diversity and composition, necessary to allow inter-site comparisons and to monitor changes, is especially difficult to reach in speciose invertebrate communities. Spatial components of the sampling design (sampling interval, extent and grain) as well as temporal variations of species density affect the measures of diversity (species richness S, Buzas and Gibson's evenness E and Shannon's heterogeneity H). Our aim was to document the small-scale spatial distribution of leaf litter ants in a subtropical dry forest of the Argentinian Chaco and analyze how the community characterization was best achieved with a minimal sampling effort. The work was based on the recent standardized protocol for collecting ants of the leaf litter ("A.L.L.": 20 samples at intervals of 10 m). To evaluate the consistency of the sampling method in time and space, the selected site was first subject to a preliminary transect, then submitted after a 9-month interval to an 8-fold oversampling campaign (160 samples at interval of 1.25 m). Leaf litter ants were extracted from elementary 1 m2 quadrats with Winkler apparatus. An increase in the number of samples collected increased S and decreased E but did not affect much H. The sampling interval and extent did not affect S and H beyond a distance of 10 m between samples. An increase of the sampling grain had a similar effect on S than a corresponding increase of the number of samples collected, but caused a proportionaly greater increase of H. The density of species m,2 varied twofold after a 9-month interval; the effect on S could only be partially corrected by rarefaction. The measure of species numerical dominance was little affected by the season. A single standardized A.L.L. transect with Winkler samples collected <45% of the species present in the assemblage. All frequent species were included but their relative frequency was not always representative. A log series distribution of species occurrences was oberved. Fisher's , and Shannon's H were the most appropriate diversity indexes. The former was useful to rarefy or abundify S and the latter was robust against sample size effects. Both parametric and Soberón and Llorente extrapolation methods outperformed non-parametric methods and yielded a fair estimate of total species richness along the transect, a minimum value of S for the habitat sampled. [source] Design-based empirical orthogonal function model for environmental monitoring data analysis,ENVIRONMETRICS, Issue 8 2008Breda Munoz Abstract An empirical orthogonal function (EOF) model is proposed as a prediction method for data collected over space and time. EOF models are widely used in a number of disciplines, including Meteorology and Oceanography. The appealing feature of this model is the advantage of not requiring any assumption for the covariance matrix structure. However, there is a need to account for the errors associated with the spatial and temporal features of the data. This is accomplished by incorporating information from the sampling design, used to establish the network, into the model. The theoretical developments and numerical solutions are presented in the first section of the paper. An application of the model to real data and the results of validation analyses are also presented. Copyright © 2008 John Wiley & Sons, Ltd. [source] Spatial sampling design under the infill asymptotic framework,ENVIRONMETRICS, Issue 4 2006Zhengyuan Zhu Abstract We study optimal sample designs for prediction with estimated parameters. Recent advances in the infill asymptotic theory provide a deeper understanding of the finite sample behavior of prediction and estimation. By incorporating these known asymptotic results, we modify some existing design criteria for estimation of covariance function and best linear unbiased prediction. These modified criteria could significantly reduce the computation time necessary for finding an optimal design. We illustrate our approach through both a real experiment in agriculture and simulation. Copyright © 2005 John Wiley & Sons, Ltd. [source] A new approach to influence diagnostics in superpopulationsENVIRONMETRICS, Issue 4 2005J. M. Fernández-Ponce Abstract Influence analysis on a model is one of the most studied topics from a frequentist viewpoint. Basically, disturbances are introduced into the model in order to measure the influence that one or a set of observations has on statistical analysis. The most common disturbance pattern is that of the omission of the observations whose influence is to be studied. In our model, we assume that there are only one or a few outliers because they may often be detected by deletion methods associated with regression diagnostics. However, these methods may fail in the presence of multiple outliers. In this case, the forward search can be used to avoid the masking and swamping problems. This article presents a Bayes approach for the influence analysis on a model in finite populations. Particularly, we develop a new approach to the study of influence in prediction theory, based on the given data rather than on the sampling design for data collection. We propose that the influence analysis on the superpopulation normal regression model and a measure based on the conditional bias from a Bayesian viewpoint is analyzed. Forward deletion formulae based on our influence measure can be defined, but this topic is beyond the scope of this article. Finally, we apply our proposed influence measure in a classic example for water contents of soil specimens. Copyright © 2005 John Wiley & Sons, Ltd. [source] Non-parametric tests and confidence regions for intrinsic diversity profiles of ecological populationsENVIRONMETRICS, Issue 8 2003Tonio Di Battista Abstract Evaluation of diversity profiles is useful for ecologists to quantify the diversity of biological communities. Measures of diversity profile can be expressed as a function of the unknown abundance vector. Thus, the estimators and related confidence regions and tests of hypotheses involve aspects of multivariate analysis. In this setting, using a suitable sampling design, inference is developed assuming an asymptotic specific distribution of the profile estimator. However, in a biological framework, ecologists work with small sample sizes, and the use of any probability distribution is hazardous. Assuming that a sample belongs to the family of replicated sampling design, we show that the diversity profile estimator can be expressed as a linear combination of the ranked abundance vector estimators. Hence we are able to develop a non-parametric approach based on a bootstrap in order to build balanced simultaneous confidence sets and tests of hypotheses for diversity profiles. Finally, the proposed procedure is applied on the avian populations of four parks in Milan, Italy. Copyright © 2003 John Wiley & Sons, Ltd. [source] Random perturbation methods applied to multivariate spatial sampling designENVIRONMETRICS, Issue 7 2001J. M. Angulo Abstract The problem of estimating a multivariate spatial random process from observations obtained by sampling a related multivariate spatial random process is considered. A method based on additive perturbation of the variables of interest is proposed for the assignment of degrees of relative importance to the variables and/or locations of interest in the design of sampling strategies. In the case where the variables involved have a multivariate Gaussian distribution, some theoretical results are provided to justify the method proposed; in particular, it is proved that the amount of information contained in the data on the perturbed variables of interest is never higher than that contained in the original variables of interest. These results and the application of the method are illustrated with an empirical study, showing the variation of the effects of perturbation on spatial sampling design configurations and related ratios of information for different degrees of dependence according to the model specifications. Copyright © 2001 John Wiley & Sons, Ltd. [source] Groundwater biodiversity patterns in the Lessinian Massif of northern ItalyFRESHWATER BIOLOGY, Issue 4 2009DIANA M. P. GALASSI Summary 1. The distribution patterns of stygobiotic invertebrates were examined with a stratified sampling design at 197 sites selected among four hydrogeographic basins in the Lessinian Massif (northern Italy). The sites were approximately evenly distributed among four hydrogeological zones: unsaturated and saturated zone of karstic aquifers, and hyporheic and saturated zone of porous aquifers. 2. Outlying Mean Index (OMI) analysis which assesses deviation of habitat conditions from reference conditions, was used to evaluate the importance of 14 selected environmental variables in shaping groundwater biodiversity patterns in the region (total of 89 stygobiotic species). The measured variables explained 80% of the variability in the data set. 3. Sampling sites were distributed along the environmental gradients defined by OMI analysis. Significant differences were detected between karstic and porous site, as well as among sites located in the four hydrogeological zones. Differences among the four hydrogeographic basins were not observed. 4. Ordination of stygobiotic species along the environmental gradients was best explained by historical variables (mainly Würmian glaciation and age of the underlying geological formation), while variables related to hydrogeology (mainly pH, calcium concentration and habitat fragmentation) influenced species distributions in the hydrogeological zones. An Environmental Integrity Index and nitrate concentration were significantly correlated with altitude, but appeared not to play a significant role in determining stygobiotic biodiversity patterns at the regional scale. 5. Results of the OMI analysis were highly significant for all taxa, suggesting that stygobiotic species are sensitive to the environmental factors studied. Thirty-five species showed high habitat specialisation (OMI index > 10). These species were usually rare and endemic to the Lessinian Massif. Most of them were found in a single hydrogeological zone. 6. Quaternary glaciations appear not to have lowered stygobiotic species richness in the Lessinian Massif. This may be because of the marginal location of the region with respect to the Würmian glacier limit and because of extensive networks of fractures in the vadose zone of the karst, which may have allowed stygobionts to move deep down in the aquifers to seek refuge during surface freezing and to recolonise ancestral habitats after the glaciers retreated. [source] Effects of hydrogeomorphic region, catchment storage and mature forest on baseflow and snowmelt stream water quality in second-order Lake Superior Basin tributariesFRESHWATER BIOLOGY, Issue 5 2003Naomi E. Detenbeck SUMMARY 1. In this study we predict stream sensitivity to non-point source pollution based on the non-linear responses of hydrological regimes and associated loadings of non-point source pollutants to catchment properties. We assessed two hydrologically based thresholds of impairment, one for catchment storage (5,10%) and one for mature forest (<50% versus >60% of catchment in mature forest cover) across two different hydrogeomorphic regions within the Northern Lakes and Forest (NLF) ecoregion: the North Shore [predominantly within the North Shore Highlands Ecological Unit] and the South Shore (predominantly within the Lake Superior Clay Plain Ecological Unit). Water quality samples were collected and analysed during peak snowmelt and baseflow conditions from 24 second-order streams grouped as follows: three in each region × catchment storage × mature forest class. 2. Water quality was affected by a combination of regional influences, catchment storage and mature forest. Regional differences were significant for suspended solids, phosphorus, nitrogen: phosphorus ratios, dissolved organic carbon (DOC) and alkalinity. Catchment storage was significantly correlated with dissolved silica during the early to mid-growing season, and with DOC, specific conductance and alkalinity during all seasons. Total nitrogen and dissolved nitrogen were consistently less in low mature forest than in high mature forest catchments. Catchment storage interacted with the influence of mature forest for only two metrics: colour and the soluble inorganic nitrogen : phosphorus ratio. 3. Significant interaction terms (region by mature forest or region by storage) suggest differences in regional sensitivity for conductance, alkalinity, total organic carbon, and colour, as well as possible shifts in thresholds of impact across region or mature forest class. 4. Use of the NLF Ecoregion alone as a basis for setting regional water quality criteria would lead to the misinterpretation of reference condition and assessment of condition. There were pronounced differences in background water quality between the North and South Shore streams, particularly for parameters related to differences in soil parent material and glacial history. A stratified random sampling design for baseflow and snowmelt stream water quality based on both hydrogeomorphic region and catchment attributes improves assessments of both reference condition and differences in regional sensitivity. [source] Functional trait variation and sampling strategies in species-rich plant communitiesFUNCTIONAL ECOLOGY, Issue 1 2010Christopher Baraloto Summary 1. ,Despite considerable interest in the application of plant functional traits to questions of community assembly and ecosystem structure and function, there is no consensus on the appropriateness of sampling designs to obtain plot-level estimates in diverse plant communities. 2. ,We measured 10 plant functional traits describing leaf and stem morphology and ecophysiology for all trees in nine 1-ha plots in terra firme lowland tropical rain forests of French Guiana (N = 4709). 3. ,We calculated, by simulation, the mean and variance in trait values for each plot and each trait expected under seven sampling methods and a range of sampling intensities. Simulated sampling methods included a variety of spatial designs, as well as the application of existing data base values to all individuals of a given species. 4. ,For each trait in each plot, we defined a performance index for each sampling design as the proportion of resampling events that resulted in observed means within 5% of the true plot mean, and observed variance within 20% of the true plot variance. 5. ,The relative performance of sampling designs was consistent for estimations of means and variances. Data base use had consistently poor performance for most traits across all plots, whereas sampling one individual per species per plot resulted in relatively high performance. We found few differences among different spatial sampling strategies; however, for a given strategy, increased intensity of sampling resulted in markedly improved accuracy in estimates of trait mean and variance. 6. ,We also calculated the financial cost of each sampling design based on data from our ,every individual per plot' strategy and estimated the sampling and botanical effort required. The relative performance of designs was strongly positively correlated with relative financial cost, suggesting that sampling investment returns are relatively constant. 7. ,Our results suggest that trait sampling for many objectives in species-rich plant communities may require the considerable effort of sampling at least one individual of each species in each plot, and that investment in complete sampling, though great, may be worthwhile for at least some traits. [source] Estimating the Variability of Active-Layer Thaw Depth in Two Physiographic Regions of Northern AlaskaGEOGRAPHICAL ANALYSIS, Issue 2 2001Claire E. Gomersall The active layer is the zone above permafrost that experiences seasonal freeze and thaw. Active-layer thickness varies annually in response to air and surface temperature, and generally decreases poleward. Substantially less is known about thaw variability across small lateral distances in response to topography, parent material, vegetation, and subsurface hydrology. A graduated steel rod was used to measure the 1998 end-of-season thaw depth across several transects. A balanced hierarchical sampling design was used to estimate the contribution to total variance in active-layer depth at separating distances of 1, 3, 9, 27, and 100 meters. A second sampling scheme was used to examine variation at shorter distances of 0.3 and 0.1 meter. This seven-stage sample design was applied to two sites in the Arctic Foothills physiographic province, and four sites on the Arctic Coastal Plain province in northern Alaska. The spatial variability for each site was determined using ANOVA and variogram methods to compare intersite and inter-province variation. Spatial variation in thaw depth was different in the Foothills and Coastal Plain sites. A greater percentage of the total variance occurs at short lag distances (0,3 meters) at the Foothills sites, presumably reflecting the influence of frost boils and tussock vegetation on ground heat flow. In contrast, thaw variation at the Coastal Plain sites occurs at distances exceeding 10 meters, and is attributed to the influence of well-developed networks of ice-wedge polygons and the presence of drained thaw-lake basins. This information was used to determine an ongoing sampling scheme for each site and to assess the suitability of each method of analysis. [source] Complications of hysterectomy in women with von Willebrand diseaseHAEMOPHILIA, Issue 4 2009A. H. JAMES Summary., Case reports and small case series suggest that women with von Willebrand disease (VWD) are at a very high risk of bleeding complications with hysterectomy. As the procedure may be beneficial to women who suffer from heavy menstrual bleeding and have completed childbearing, an understanding of the true risks involved is essential for appropriate decision making. To estimate the incidence of bleeding and other complications in women with VWD who undergo hysterectomy. The United States Nationwide Inpatient Sample (NIS) from the Healthcare Cost and Utilization Project of the Agency for Healthcare Research and Quality for the years 1988,2004 was queried for all hysterectomies for non-malignant conditions. Data were analysed based on the NIS sampling design. Bivariate analyses were used to examine the differences between women with and without VWD. Multivariate analysis was used to adjust for potential confounders among women who underwent hysterectomy for heavy menstrual bleeding. 545 of the 1 358 133 hysterectomies were to women with VWD. Women with VWD were significantly more likely to experience intraoperative and postoperative bleeding (2.75% vs. 0.89%, P < 0.001) and require transfusion (7.34% vs. 2.13%, P < 0.001) than women without VWD. One woman with VWD died. While the risk of bleeding complications from hysterectomy in women with VWD is smaller than previously reported, women with VWD did experience significantly more bleeding complications than women without VWD. Nonetheless, for women who have completed childbearing, the risks of hysterectomy may be acceptable. [source] The Effects of Geography and Spatial Behavior on Health Care Utilization among the Residents of a Rural RegionHEALTH SERVICES RESEARCH, Issue 1 2005Thomas A. Arcury Objective. This analysis determines the importance of geography and spatial behavior as predisposing and enabling factors in rural health care utilization, controlling for demographic, social, cultural, and health status factors. Data Sources. A survey of 1,059 adults in 12 rural Appalachian North Carolina counties. Study Design. This cross-sectional study used a three-stage sampling design stratified by county and ethnicity. Preliminary analysis of health services utilization compared weighted proportions of number of health care visits in the previous 12 months for regular check-up care, chronic care, and acute care across geographic, sociodemographic, cultural, and health variables. Multivariable logistic models identified independent correlates of health services utilization. Data Collection Methods. Respondents answered standard survey questions. They located places in which they engaged health related and normal day-to-day activities; these data were entered into a geographic information system for analysis. Principal Findings. Several geographic and spatial behavior factors, including having a driver's license, use of provided rides, and distance for regular care, were significantly related to health care utilization for regular check-up and chronic care in the bivariate analysis. In the multivariate model, having a driver's license and distance for regular care remained significant, as did several predisposing (age, gender, ethnicity), enabling (household income), and need (physical and mental health measures, number of conditions). Geographic measures, as predisposing and enabling factors, were related to regular check-up and chronic care, but not to acute care visits. Conclusions. These results show the importance of geographic and spatial behavior factors in rural health care utilization. They also indicate continuing inequity in rural health care utilization that must be addressed in public policy. [source] Hepatitis C infection in hemodialysis patients in Iran: A systematic reviewHEMODIALYSIS INTERNATIONAL, Issue 3 2010Seyed-Moayed ALAVIAN Abstract Hemodialysis (HD) patients are recognized as one of the high-risk groups for hepatitis C virus (HCV) infection. The prevalence of HCV infection varies widely between 5.5% and 24% among different Iranian populations. Preventive programs for reducing HCV infection prevalence in these patients require accurate information. In the present study, we estimated HCV infection prevalence in Iranian HD patients. In this systematic review, we collected all published and unpublished documents related to HCV infection prevalence in Iranian HD patients from April 2001 to March 2008. We selected descriptive/analytic cross-sectional studies/surveys that have sufficiently declared objectives, a proper sampling method with identical and valid measurement instruments for all study subjects, and proper analysis methods regarding sampling design and demographic adjustments. We used a meta-analysis method to calculate nationwide prevalence estimation. Eighteen studies from 12 provinces (consisting 49.02% of the Iranian total population) reported the prevalence of HCV infection in Iranian HD patients. The HCV infection prevalence in Iranian HD patients is 7.61% (95% confidence interval: 6.06,9.16%) with the recombinant immunoblot assay method. Iran is among countries with low HCV infection prevalence in HD patients. [source] Spatial variations in throughfall in a Moso bamboo forest: sampling design for the estimates of stand-scale throughfallHYDROLOGICAL PROCESSES, Issue 3 2010Yoshinori Shinohara Abstract We investigated the spatial and seasonal variations in throughfall (Tf) in relation to spatial and seasonal variations in canopy structure and gross rainfall (Rf) and assessed the impacts of the variations in Tf on stand-scale Tf estimates. We observed the canopy structure expressed as the leaf area index (LAI) once a month and Tf once a week in 25 grids placed in a Moso bamboo (Phyllostachys pubescens) forest for 1 year. The mean LAI and spatial variation in LAI did have some seasonal variations. The spatial variations in Tf reduced with increasing Rf, and the relationship between the spatial variation and the Rf held throughout the year. These results indicate that the seasonal change in LAI had little impact on spatial variations in Tf, and that Rf is a critical factor determining the spatial variations in Tf at the study site. We evaluated potential errors in stand-scale Tf estimates on the basis of measured Tf data using Monte Carlo sampling. The results showed that the error decreases greatly with increasing sample size when the sample size was less than ,8, whereas it was near stable when the sample size was 8 or more, regardless of Rf. A sample size of eight results in less than 10% error for Tf estimates based on Student's t -value analysis and would be satisfactory for interception loss estimates when considering errors included in Rf data. Copyright © 2009 John Wiley & Sons, Ltd. [source] Technical issues affecting the implementation of US Environmental Protection Agency's proposed fish tissue-based aquatic criterion for selenium,INTEGRATED ENVIRONMENTAL ASSESSMENT AND MANAGEMENT, Issue 4 2007A Dennis Lemly Abstract The US Environmental Protection Agency is developing a national water quality criterion for selenium that is based on concentrations of the element in fish tissue. Although this approach offers advantages over the current water-based regulations, it also presents new challenges with respect to implementation. A comprehensive protocol that answers the "what, where, and when" is essential with the new tissue-based approach in order to ensure proper acquisition of data that apply to the criterion. Dischargers will need to understand selenium transport, cycling, and bioaccumulation in order to effectively monitor for the criterion and, if necessary, develop site-specific standards. This paper discusses 11 key issues that affect the implementation of a tissue-based criterion, ranging from the selection of fish species to the importance of hydrological units in the sampling design. It also outlines a strategy that incorporates both water column and tissue-based approaches. A national generic safety-net water criterion could be combined with a fish tissue,based criterion for site-specific implementation. For the majority of waters nationwide, National Pollution Discharge Elimination System permitting and other activities associated with the Clean Water Act could continue without the increased expense of sampling and interpreting biological materials. Dischargers would do biotic sampling intermittently (not a routine monitoring burden) on fish tissue relative to the fish tissue criterion. Only when the fish tissue criterion is exceeded would a full site-specific analysis including development of intermedia translation factors be necessary. [source] Evaluating screening questionnaires using receiver Operating Characteristic (ROC) curves from two-phase (double) samplesINTERNATIONAL JOURNAL OF METHODS IN PSYCHIATRIC RESEARCH, Issue 3 2000Giulia Bisoffi Abstract The characteristics of psychiatric screening tests (for example, sensitivity, specificity, and AUC , the area under an ROC curve) are frequently assessed using data arising from two-phase samples. Too often, however, the statistical methods that are used are incorrect. They do not appropriately account for the sampling design. Valid methods for the estimate of sensitivity, specificity and, in particular, the AUC, together with its standard error, are discussed in detail and a Stata macro for the implementation of these methods is provided. Simple weighting procedures are used to correct for verification biases arising from the two-phase design, together with bootstrap or jackknife sampling for the calculation of valid standard errors. Copyright © 2000 Whurr Publishers Ltd. [source] Local,regional boundary shifts in oribatid mite (Acari: Oribatida) communities: species,area relationships in arboreal habitat islands of a coastal temperate rain forest, Vancouver Island, CanadaJOURNAL OF BIOGEOGRAPHY, Issue 9 2007Zoë Lindo Abstract Aim, This study investigates the species,area relationship (SAR) for oribatid mite communities of isolated suspended soil habitats, and compares the shape and slope of the SAR with a nested data set collected over three spatial scales (core, patch and tree level). We investigate whether scale dependence is exhibited in the nested sampling design, use multivariate regression models to elucidate factors affecting richness and abundance patterns, and ask whether the community composition of oribatid mites changes in suspended soil patches of different sizes. Location, Walbran Valley, Vancouver Island, Canada. Methods, A total of 216 core samples were collected from 72 small, medium and large isolated suspended soil habitats in six western redcedar trees in June 2005. The relationship between oribatid species richness and habitat volume was modelled for suspended soil habitat isolates (type 3) and a nested sampling design (type 1) over multiple spatial scales. Nonlinear estimation parameterized linear, power and Weibull function regression models for both SAR designs, and these were assessed for best fit using R2 and Akaike's information criteria (,AIC) values. Factors affecting oribatid mite species richness and standardized abundance (number per g dry weight) were analysed by anova and linear regression models. Results, Sixty-seven species of oribatid mites were identified from 9064 adult specimens. Surface area and moisture content of suspended soils contributed to the variation in species richness, while overall oribatid mite abundance was explained by moisture and depth. A power-law function best described the isolate SAR (S = 3.97 × A0.12, R2 = 0.247, F1,70 = 22.450, P < 0.001), although linear and Weibull functions were also valid models. Oribatid mite species richness in nested samples closely fitted a power-law model (S = 1.96 × A0.39, R2 = 0.854, F1,18 = 2693.6, P < 0.001). The nested SAR constructed over spatial scales of core, patch and tree levels proved to be scale-independent. Main conclusions, Unique microhabitats provided by well developed suspended soil accumulations are a habitat template responsible for the diversity of canopy oribatid mites. Species,area relationships of isolate vs. nested species richness data differed in the rate of accumulation of species with increased area. We suggest that colonization history, stability of suspended soil environments, and structural habitat complexity at local and regional scales are major determinants of arboreal oribatid mite species richness. [source] Comparison between two sampling methods to evaluate the structure of fish communities in the littoral zone of a Laurentian lakeJOURNAL OF FISH BIOLOGY, Issue 5 2004A. Brind'Amour The results of beach seining were compared with visual surveys, in habitats showing a gradient of macrophyte densities in Lake Drouin, Québec, Canada. Six community descriptors (species density, total fish density, relative abundance per species, presence or absence of given species, size structure of the fish community and total biomass of the fish community) were used to compare the sampling methods. Most of the fish community descriptors obtained by visual surveys were estimated with an accuracy similar to that of beach seining. Both methods sampled the same number of species (eight out of nine). Visual surveys assessed the relative abundance of the yellow perch Perca flavescens and white sucker Catostomus commersoni with an higher accuracy than the beach seine. The greatest discrepancies between the two sampling methods were for total fish density and the total fish biomass. Because of the sampling strategy, both descriptors were underestimated by visual surveys, notably in the higher macrophyte density. In a broad community survey to determine the relative importance of species abundance, the visual survey was effective and could be used to develop a within-lake regular and fine-scale sampling design of the spatial arrangement of fish communities and their habitats. [source] Prevalence of hepatitis B and hepatitis C virus infections in France in 2004: Social factors are important predictors after adjusting for known risk factorsJOURNAL OF MEDICAL VIROLOGY, Issue 4 2010Christine Meffre Abstract To monitor the prevalence of hepatitis B and hepatitis C a cross-sectional survey was conducted in 2004 among French metropolitan residents. A complex sampling design was used to enroll 14,416 adult participants aged 18,80 years. Data collected included demographic and social characteristics and risk factors. Sera were tested for anti-HCV, HCV-RNA, anti-HBc and HBsAg. Data were analyzed with SUDAAN® software to provide weighted estimates for the French metropolitan resident population. The overall anti-HCV prevalence was 0.84% (95% CI: 0.65,1.10). Among anti-HCV positive individuals, 57.4% (95% CI: 43.2,70.5) knew their status. Factors associated independently with positive anti-HCV were drug use (intravenous and nasal), blood transfusion before 1992, a history of tattoos, low socioeconomic status, being born in a country where anti-HCV prevalence >2.5%, and age >29 years. The overall anti-HBc prevalence was 7.3% (95%: 6.5,8.2). Independent risk factors for anti-HBc were intravenous drug use, being a man who has sex with men, low socioeconomic status, a stay in a psychiatric facility or facility for the mentally disabled, <12 years of education, being born in a country where HBsAg prevalence >2%, age >29 and male sex. The HCV RNA and HBsAg prevalence were 0.53% (95% CI: 0.40,0.70) and 0.65% (95% CI: 0.45,0.93), respectively. Among HBsAg positive individuals, 44.8% (95% CI: 22.8,69.1) knew their status. Anti-HCV prevalence was close to the 1990s estimates whereas HBsAg prevalence estimate was greater than expected. Screening of hepatitis B and C should be strengthened and should account for social vulnerability. J. Med. Virol. 82:546,555, 2010. © 2010 Wiley-Liss, Inc. [source] Scale-dependence of vegetation-environment relationships in semi-natural grasslandsJOURNAL OF VEGETATION SCIENCE, Issue 1 2008Inger Auestad Abstract Questions: Which environmental and management factors determine plant species composition in semi-natural grasslands within a local study area? Are vegetation and explanatory factors scale-dependent? Location: Semi-natural grasslands in Lærdal, Sognog Fjordane County, western Norway. Methods: We recorded plant species composition and explanatory variables in six grassland sites using a hierarchically nested sampling design with three levels: plots randomly placed within blocks selected within sites. We evaluated vegetation-environment relationships at all three levels by means of DCA ordination and split-plot GLM analyses. Results: The most important complex gradient determining variation in grassland species composition showed a broad-scale relationship with management. Soil moisture conditions were related to vegetation variation on block scale, whereas element concentrations in the soil were significantly related to variation in species composition on all spatial scales. Our results show that vegetation-environment relationships are dependent on the scale of observation. We suggest that scale-related (and therefore methodological) issues may explain the wide range of vegetation-environment relationships reported in the literature, for semi-natural grassland in particular but also for other ecosystems. Conclusions: Interpretation of the variation in species composition of semi-natural grasslands requires consideration of the spatial scales on which important environmental variables vary. [source] Metals in the sediments of the Huron-Erie Corridor in North America: Factors regulating metal distribution and mobilizationLAKES & RESERVOIRS: RESEARCH AND MANAGEMENT, Issue 4 2007Ewa Szalinska Abstract Sediment samples from the Huron-Erie Corridor (Great Lakes, North America) were collected to quantify the relative importance of natural and anthropogenic sources of contamination, and to study the spatial metal distribution patterns of metals as a function of the characteristics of the Corridor sediments. A stratified random sampling design was used to measure the spatial patterns of metal inputs, settling and sorting along the length of the Corridor. Factors regulating metal mobilization were assessed by determining metal affinities with the total organic fraction (TOM), the mineral fraction (represented as Al), and the granulometric characteristic (represented as <0.063 mm fraction). The study revealed that anthropogenic factors primarily regulated metal distributions and mobilization throughout the Huron-Erie Corridor. In the St. Clair and Detroit Rivers, the spatial pattern of metal distributions strongly reflected local industrial sources. In the Walpole Delta and Lake St. Clair, however, inorganic (clays) and organic (TOM) particles dominated the contaminant distribution. Sediment contamination issues throughout the Huron-Erie Corridor were dominated by mercury, released from sources along the St. Clair and Detroit Rivers. The mean enrichment factor EFAl for mercury in these sediments has reached 68.3. Other metal pollutants were confined to the sediments in the lower depositional reach of the Corridor. [source] Recent innovations in marine biologyMARINE ECOLOGY, Issue 2009Ferdinando Boero Abstract Modern ecology arose from natural history when Vito Volterra analysed Umberto D'Ancona's time series of Adriatic fisheries, formulating the famous equations describing the linked fluctuations of a predator,prey system. The shift from simple observation to careful sampling design, and hypothesis building and testing, often with manipulative approaches, is probably the most relevant innovation in ecology, leading from descriptive to experimental studies, with the use of powerful analytical tools to extract data (from satellites to molecular analyses) and to treat them, and modelling efforts leading to predictions. However, the historical component, time, is paramount in environmental systems: short-term experiments must cope with the long term if we want to understand change. Chaos theory showed that complex systems are inherently unpredictable: equational, predictive science is only feasible over the short term and for a small number of variables. Ecology is characterized by a high number of variables (e.g. species) interacting over wide temporal and spatial scales. The greatest recent conceptual innovation, thus, is to have realized that natural history is important, and that the understanding of complexity calls for humility. This is not a return to the past, because now we can give proper value to statistical approaches aimed at formalizing the description and the understanding of the natural world in a rigorous way. Predictions can only be weak, linked to the identification of the attractors of chaotic systems, and are aimed more at depicting scenarios than at forecasting the future with precision. Ecology was originally split into two branches: autecology (ecology of species) and synecology (ecology of species assemblages, communities, ecosystems). The two approaches are almost synonymous with the two fashionable concepts of today: ,biodiversity' and ,ecosystem functioning'. A great challenge is to put the two together and work at multiple temporal and spatial scales. This requires the identification of all variables (i.e. species and their ecology: biodiversity, or autoecology) and of all connections among them and with the physical world (i.e. ecosystem functioning, or synecology). Marine ecosystems are the least impacted by human pressures, compared to terrestrial ones, and are thus the best arena to understand the structure and function of the natural world, allowing for comparison between areas with and areas without human impact. [source] Variability in the structure of epiphytic assemblages of the Mediterranean seagrass Posidonia oceanica in relation to depthMARINE ECOLOGY, Issue 3 2009Ugo Nesti Abstract The aim of the present study was to evaluate whether the variability in the structure of the epiphytic assemblages of leaves and rhizomes of the Mediterranean seagrass Posidonia oceanica differed between depths at a large spatial scale. A hierarchical sampling design was used to compare epiphytic assemblages at two different depths (10 and 20 m) in terms of both species composition and abundance and patterns of spatial variability in the Tuscan Archipelago (North Western Mediterranean Sea, Italy). Results showed significant differences in the structure of assemblages on rhizomes and leaves at different depths. These differences were related to species composition and abundance; differences were not significant for total biomass, total percentage cover and percentage cover of animals and algae. Whereas the higher variability was observed among shoots in all the studied systems, patterns of spatial variability at the other spatial scales investigated differed between the two studied depths. Moreover, in the present study, analogous patterns between depths resulted for both the assemblages of leaves and rhizomes, suggesting that factors that change with depth can be responsible for the spatial variability of both the assemblages (leaves and rhizomes), and operate regardless of the microclimatic conditions and the structure of assemblages. [source] | |||||||||||||||||||||||||||||||||||||||||||