Estimation for two-phase longitudinal surveys with application to the National Resources Inventory

Many longitudinal surveys can be represented as two-phase samples, where the entire set of observed units can be considered to be a first-phase sample and the second-phase samples are panels that are observed at times determined by an observation scheme. Common longitudinal schemes such as pure panel, rotating panels, and supplemented panels fit this two-phase sample description. We propose a cell-mean model with a fixed number of time points and panels where the model links the vector of second-phase panel means to the vector of time point population means. Covariance matrix estimation techniques that rely on fitting theoretical autocovariance functions to empirical covariances using nonlinear least squares are presented. A method for pooling covariance estimators across partially overlapping panels is described. The estimated generalized least squares estimator (EGLSE) is proposed for the vector of time means. Given a consistent first-phase replication variance estimator, the properties of a consistent replication estimator for the variance of the EGLSE are derived. A central limit theorem for the mean vector is given for the EGLSE under stratified fixed-rate second-phase sampling. We examine weight adjustments and imputation procedures for creating an output dataset that reflects the EGLSEs for key variables. Weight adjustment through regression estimation is proposed for a dataset containing a panel that is always observed and the replication variance estimator is extended to the regression estimator. For constructing a complete dataset, we consider imputation methods where the imputed values are chosen so that the weighted total equals the EGLSE. Results are illustrated using the National Resources Inventory, which has a supplemented panel design

A calibration experiment in a longitudinal survey with errors-in-variables

The National Resources Inventory (NRI) is a large-scale longitudinal survey conducted to assess trends and conditions of nonfederal land. A key NRI estimate is year-to-year change in acres of developed land, where developed land includes roads and urban areas. In 2003, a digital data collection procedure was implemented replacing a map overlay. Data from an NRI calibration experiment are used to estimate the relationship between data collected under the old and new protocols. A measurement error model is postulated for the relationship, where duplicate measurements are used to estimate one of the error variances. If any significant discrepancy is detected between new and old measures, some parameters that govern the algorithm under new protocol can be changed to alter the relationship. Parameters were calibrated so overall averages nearly match for the new and old protocols. Analyses on the data after initial parameter calibration suggest that the relationship is a line with an intercept of zero and a slope of one, therefore the parameters currently used are acceptable. The paper also provides models of the measurement error variances as functions of the proportion of developed land, which is essential for estimating the effect of measurement error for the whole NRI data

Assessment of Expert Opinion: Seasonal Sheep Preference and Plant Response to Grazing

Expert opinion was sought on two issues relating to herbivory: seasonal sheep preferences for plant species and seasonal plant response to grazing. Expert opinion is commonly used to parameterize models: it is therefore important to assess its quality. Understanding the limitations of expert knowledge can allow prioritization of future research. Nine experts in plant or grazing ecology from Scotland/Northern England were individually interviewed. The experts ranked sheep preferences for species in four rangeland vegetation types and provided categorical information on plant response to grazing. For both issues, seasonal information was collected. Uncertainty (unanswered questions) on plant responses was much higher than uncertainty on sheep preferences. Uncertainty on sheep preference was significantly negatively correlated with plant species commonness, but not with quantity of scientific literature. Uncertainty on plant responses was significantly negatively correlated with both plant commonness and literature. There was agreement between experts on sheep preferences; standardized seasonal information for selected plant species is presented. In general, experts considered graminoids to be preferred over dwarf shrubs, with forbs and other species groups intermediate. Seasonal variation in sheep preference was greater for heath and mire than for grasslands. There was limited agreement between experts on seasonal plant responses. Some experts considered grazing in summer to affect growth more than grazing in winter, while others thought season had little effect. Sufficient agreement was found at the species level to present results on plant responses. Experts considered graminoids more resilient to grazing than dwarf shrubs. Experts agreed on sheep preference at different times of year, and on the overall resilience of plant species to grazing. However, the experts held two paradigms on the impact of seasonal grazing. Further research is required to explore this, since seasonal grazing regimes are currently promoted as conservation management tools

Impacts of livestock in regenerating upland birch woodlands in Scotland

Including large herbivores in wooded areas is often seen as a useful conservation tool. Browsing intensities on saplings in seven upland birch woodlands grazed by sheep, cattle and wild herbivores were studied. The aims were to determine whether tree regeneration could occur in the presence of livestock, particularly sheep, and the conditions under which stock can be grazed sustainably within woodlands. The results showed that regeneration can occur at sites grazed by livestock. Within-site variation in the proportion of shoots browsed per sapling was high, but significant trends were detected. Browsing intensity was negatively related to good quality biomass per livestock unit, basal diameter and adjacent vegetation height. Saplings with a topiaried growth form were browsed more than saplings with a normal growth form. When writing management plans, stocking densities should be set in relation to forage quantity and quality. Understanding the relationship between good quality biomass per livestock unit and browsing intensity will facilitate more sustainable management of grazing within woodlands

Special Issue "On Defining Artificial Intelligence"—Commentaries and Author's Response

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Aqueous Dissolution of Alzheimer's Disease Ab Amyloid Deposits by Biometal Depletion

Zn(II) and Cu(II) precipitate Abeta in vitro into insoluble aggregates that are dissolved by metal chelators. We now report evidence that these biometals also mediate the deposition of Abeta amyloid in Alzheimer's disease, since the solubilization of Abeta from post-mortem brain tissue was significantly increased by the presence of chelators, EGTA, N,N,N',N'-tetrakis(2-pyridyl-methyl) ethylene diamine, and bathocuproine. Efficient extraction of Abeta also required Mg(II) and Ca(II). The chelators were more effective in extracting Abeta from Alzheimer's disease brain tissue than age-matched controls, suggesting that metal ions differentiate the chemical architecture of amyloid in Alzheimer's disease. Agents that specifically chelate copper and zinc ions but preserve Mg(II) and Ca(II) may be of therapeutic value in Alzheimer's disease

Symptom-based stratification of patients with primary Sjögren's syndrome: multi-dimensional characterisation of international observational cohorts and reanalyses of randomised clinical trials

Background Heterogeneity is a major obstacle to developing effective treatments for patients with primary Sjögren's syndrome. We aimed to develop a robust method for stratification, exploiting heterogeneity in patient-reported symptoms, and to relate these differences to pathobiology and therapeutic response. Methods We did hierarchical cluster analysis using five common symptoms associated with primary Sjögren's syndrome (pain, fatigue, dryness, anxiety, and depression), followed by multinomial logistic regression to identify subgroups in the UK Primary Sjögren's Syndrome Registry (UKPSSR). We assessed clinical and biological differences between these subgroups, including transcriptional differences in peripheral blood. Patients from two independent validation cohorts in Norway and France were used to confirm patient stratification. Data from two phase 3 clinical trials were similarly stratified to assess the differences between subgroups in treatment response to hydroxychloroquine and rituximab. Findings In the UKPSSR cohort (n=608), we identified four subgroups: Low symptom burden (LSB), high symptom burden (HSB), dryness dominant with fatigue (DDF), and pain dominant with fatigue (PDF). Significant differences in peripheral blood lymphocyte counts, anti-SSA and anti-SSB antibody positivity, as well as serum IgG, κ-free light chain, β2-microglobulin, and CXCL13 concentrations were observed between these subgroups, along with differentially expressed transcriptomic modules in peripheral blood. Similar findings were observed in the independent validation cohorts (n=396). Reanalysis of trial data stratifying patients into these subgroups suggested a treatment effect with hydroxychloroquine in the HSB subgroup and with rituximab in the DDF subgroup compared with placebo. Interpretation Stratification on the basis of patient-reported symptoms of patients with primary Sjögren's syndrome revealed distinct pathobiological endotypes with distinct responses to immunomodulatory treatments. Our data have important implications for clinical management, trial design, and therapeutic development. Similar stratification approaches might be useful for patients with other chronic immune-mediated diseases. Funding UK Medical Research Council, British Sjogren's Syndrome Association, French Ministry of Health, Arthritis Research UK, Foundation for Research in Rheumatology

Grike-roclimates

This article is not available through ChesterRepThis journal article discusses data collected at two north Wales sites that demonstrates that the direction of grikes makes a significant difference on the biodiversity of limestone pavements

Microclimate & limestone pavement biodiversity: A pilot project to look at the longterm effects of grike orientation on microclimate and biodiversity in North Wales

This report is not available through ChesterRep.A long-term project (two years initially) was set up to produce a valuable database of microclimate data across two complete seasonal changes through two winter and summer soltices. The results of the project to date are: grike orientation has the potential to greatly affect the vegetation within the grikes and influence both the timing of its germination, growth and development; the bottom of the grike sufferts less temperatire fluctuation than the surface; there is a significant difference in the solar ration at 57 cm depth between the winter solstice and Mid February 1999; the range of bottom temperatures is significatnly higher in the north-south grikes during the winter months; north-south grikes suffer lower minumum temperatures during the autumn months. Grikes at Y Taranau and Bryn Pydew nature reserve were analysed