Threshold models have a wide variety of applications in economics. Direct applications include models of separating and multiple equilibria. Other applications include empirical sample splitting when ...the sample split is based on a continuously-distributed variable such as firm size. In addition, threshold models may be used as a parsimonious strategy for nonparametric function estimation. For example, the threshold autoregressive model (TAR) is popular in the nonlinear time series literature. Threshold models also emerge as special cases of more complex statistical frameworks, such as mixture models, switching models, Markov switching models, and smooth transition threshold models. It may be important to understand the statistical properties of threshold models as a preliminary step in the development of statistical tools to handle these more complicated structures. Despite the large number of potential applications, the statistical theory of threshold estimation is undeveloped. It is known that threshold estimates are super-consistent, but a distribution theory useful for testing and inference has yet to be provided. This paper develops a statistical theory for threshold estimation in the regression context. We allow for either cross-section or time series observations. Least squares estimation of the regression parameters is considered. An asymptotic distribution theory for the regression estimates (the threshold and the regression slopes) is developed. It is found that the distribution of the threshold estimate is nonstandard. A method to construct asymptotic confidence intervals is developed by inverting the likelihood ratio statistic. It is shown that this yields asymptotically conservative confidence regions. Monte Carlo simulations are presented to assess the accuracy of the asymptotic approximations. The empirical relevance of the theory is illustrated through an application to the multiple equilibria growth model of Durlauf and Johnson (1995).
Glucocorticoid-induced osteoporosis (GIOP) is the most common form of secondary osteoporosis. In May 2018, denosumab was approved for the treatment of GIOP in men and women at high risk of fracture. ...We undertook a systematic review and meta-analysis to summarize the efficacy and safety of denosumab in the prevention and treatment of GIOP.
We searched PubMed, CINAHL, American College of Rheumatology and American Society for Bone and Mineral Research meeting abstracts for relevant studies. We included studies in which subjects were taking systemic glucocorticoid therapy and were assigned to take denosumab or control therapy, and assessed the effect of treatment on areal bone mineral density (BMD), fractures and/or safety.
Three eligible studies were included in the primary meta-analysis. Denosumab significantly increased lumbar spine BMD (2.32%, 95% CI 1.73%, 2.91%,
<0.0001) and hip BMD (1.52%, 95% CI 1.1%,1.94%,
<0.0001) compared to bisphosphonates. Adverse events, serious adverse events and fractures were similar between denosumab and bisphosphonate arms.
Results suggest that denosumab is superior to bisphosphonates in its effects on lumbar spine and total hip BMD in patients with GIOP. There was no difference in the incidence of infections, adverse events or serious adverse events. Studies were underpowered to detect differences in the risk of fracture. Denosumab is a reasonable option for treatment of GIOP. However, further studies are needed to guide transitions off denosumab.
We present an approach for head MR-based attenuation correction (AC) based on the Statistical Parametric Mapping 8 (SPM8) software, which combines segmentation- and atlas-based features to provide a ...robust technique to generate attenuation maps (μ maps) from MR data in integrated PET/MR scanners.
Coregistered anatomic MR and CT images of 15 glioblastoma subjects were used to generate the templates. The MR images from these subjects were first segmented into 6 tissue classes (gray matter, white matter, cerebrospinal fluid, bone, soft tissue, and air), which were then nonrigidly coregistered using a diffeomorphic approach. A similar procedure was used to coregister the anatomic MR data for a new subject to the template. Finally, the CT-like images obtained by applying the inverse transformations were converted to linear attenuation coefficients to be used for AC of PET data. The method was validated on 16 new subjects with brain tumors (n = 12) or mild cognitive impairment (n = 4) who underwent CT and PET/MR scans. The μ maps and corresponding reconstructed PET images were compared with those obtained using the gold standard CT-based approach and the Dixon-based method available on the Biograph mMR scanner. Relative change (RC) images were generated in each case, and voxel- and region-of-interest-based analyses were performed.
The leave-one-out cross-validation analysis of the data from the 15 atlas-generation subjects showed small errors in brain linear attenuation coefficients (RC, 1.38% ± 4.52%) compared with the gold standard. Similar results (RC, 1.86% ± 4.06%) were obtained from the analysis of the atlas-validation datasets. The voxel- and region-of-interest-based analysis of the corresponding reconstructed PET images revealed quantification errors of 3.87% ± 5.0% and 2.74% ± 2.28%, respectively. The Dixon-based method performed substantially worse (the mean RC values were 13.0% ± 10.25% and 9.38% ± 4.97%, respectively). Areas closer to the skull showed the largest improvement.
We have presented an SPM8-based approach for deriving the head μ map from MR data to be used for PET AC in integrated PET/MR scanners. Its implementation is straightforward and requires only the morphologic data acquired with a single MR sequence. The method is accurate and robust, combining the strengths of both segmentation- and atlas-based approaches while minimizing their drawbacks.
Aim
To investigate how children with cerebral palsy (CP) perform in the Danish school system and which factors are associated with school performance.
Method
This was a population‐based cohort study ...including 463 126 children born from 1997 to 2003. Data were extracted from seven national registries. The study encompassed 818 children with CP (483 59.0% males, 335 41.0% females) and 417 731 without CP (214 535 51.4% males, 203 196 48.6% females). We evaluated two primary outcomes: not completing 10 years of elementary school, defined as attending fewer than eight final mandatory exams; and grade point averages (GPAs). Mann–Whitney U tests were used to analyse differences in GPAs and logistic regressions were used to calculate odds ratios (ORs).
Results
Among children with and without CP, 62.6% and 12.4% did not complete elementary school respectively (OR = 11.85 10.28–13.66). Additionally, children with CP who attended all final exams achieved lower overall GPAs than children without CP (6.6 vs 7.3, p = 0.001). In children with CP, comorbidities, maternal education, severity of motor impairments, and intellectual deficits were associated with increased odds of not completing elementary school. Notably, one‐third of children with CP with apparent normal intelligence did not complete school, despite special educational measures.
Interpretation
Danish children with CP rarely complete elementary school despite initiatives for a more supportive educational system. The complexity of individual needs in children with CP may be challenging for an inclusive school environment.
What this paper adds
Children with cerebral palsy (CP) have a high risk of not completing elementary school.
Children with CP achieve lower overall grades than children without CP.
Motor impairment, comorbidities, and maternal education are associated with poor school performance.
Intellectual impairment is the most important predictor of poor school performance.
What this paper adds
Children with cerebral palsy (CP) have a high risk of not completing elementary school.
Children with CP achieve lower overall grades than children without CP.
Motor impairment, comorbidities, and maternal education are associated with poor school performance.
Intellectual impairment is the most important predictor of poor school performance.
This original article is commented on by Lebeer on pages 1273–1274 of this issue.
Gut microbiota from individuals in rural, non-industrialized societies differ from those in individuals from industrialized societies. Here, we use 16S rRNA sequencing to survey the gut bacteria of ...seven non-industrialized populations from Tanzania and Botswana. These include populations practicing traditional hunter-gatherer, pastoralist, and agropastoralist subsistence lifestyles and a comparative urban cohort from the greater Philadelphia region.
We find that bacterial diversity per individual and within-population phylogenetic dissimilarity differs between Botswanan and Tanzanian populations, with Tanzania generally having higher diversity per individual and lower dissimilarity between individuals. Among subsistence groups, the gut bacteria of hunter-gatherers are phylogenetically distinct from both agropastoralists and pastoralists, but that of agropastoralists and pastoralists were not significantly different from each other. Nearly half of the Bantu-speaking agropastoralists from Botswana have gut bacteria that are very similar to the Philadelphian cohort. Based on imputed metagenomic content, US samples have a relative enrichment of genes found in pathways for degradation of several common industrial pollutants. Within two African populations, we find evidence that bacterial composition correlates with the genetic relatedness between individuals.
Across the cohort, similarity in bacterial presence/absence compositions between people increases with both geographic proximity and genetic relatedness, while abundance weighted bacterial composition varies more significantly with geographic proximity than with genetic relatedness.
This paper examines a two-regime vector error-correction model with a single cointegrating vector and a threshold effect in the error-correction term. We propose a relatively simple algorithm to ...obtain maximum likelihood estimation of the complete threshold cointegration model for the bivariate case. We propose a SupLM test for the presence of a threshold. We derive the null asymptotic distribution, show how to simulate asymptotic critical values, and present a bootstrap approximation. We investigate the performance of the test using Monte Carlo simulation, and find that the test works quite well. Applying our methods to the term structure model of interest rates, we find strong evidence for a threshold effect.
While the Cenozoic Afro-Arabian Rift System (AARS) has been the focus of numerous studies, it has long been questioned if low-velocity anomalies in the upper mantle beneath eastern Africa and western ...Arabia are connected, forming one large anomaly, and if any parts of the anomalous upper mantle structure extend into the lower mantle. To address these questions, we have developed a new image of P-wave velocity variations in the Afro-Arabian mantle using an adaptively parameterized tomography approach and an expanded dataset containing travel-times from earthquakes recorded on many new temporary and permanent seismic networks. Our model shows a laterally continuous, low-velocity region in the upper mantle beneath all of eastern Africa and western Arabia, extending to depths of ~500–700km, as well as a lower mantle anomaly beneath southern Africa that rises from the core-mantle boundary to at least ~1100km depth and possibly connects to the upper mantle anomaly across the transition zone. Geodynamic models which invoke one or more discrete plumes to explain the origin of the AARS are difficult to reconcile with the lateral and depth extent of the upper mantle low-velocity region, as are non-plume models invoking small-scale convection passively induced by lithospheric extension or by edge-flow around thick cratonic lithosphere. Instead, the low-velocity anomaly beneath the AARS can be explained by the African superplume model, where the anomalous upper mantle structure is a continuation of a large, thermo-chemical upwelling in the lower mantle beneath southern Africa. These findings provide further support for a geodynamic connection between processes in Earth's lower mantle and continental break-up within the AARS.
► Low velocities beneath eastern Africa and Arabia extend to depths of ~500–700km. ► The superplume anomaly rises from the core-mantle boundary to at least ~1100km. ► These findings constrain origin models for the Afro-Arabian Rift System (AARS). ► The tomographic results are most consistent with the superplume model. ► Continental break-up in the AARS is connected to processes in Earth's lower mantle.
Background & Aims We aimed to validate the fatty liver index (FLI), an algorithm that is based on waist circumference, body mass index, and levels of triglyceride and γ-glutamyltransferase. We ...calculated its ability to identify fatty liver disease from any cause or nonalcoholic fatty liver disease (NAFLD) in a large population of white elderly persons. Methods We collected ultrasonography and FLI data from participants of the Rotterdam Study from February 2009 to February 2012; 2652 subjects (mean age, 76.3 ± 6.0 years) were interviewed and received a clinical examination that included abdominal ultrasound, analysis of blood samples during fasting, and anthropometric assessment. The ability of the FLI to detect (nonalcoholic) fatty liver was assessed by using area under the receiver operator characteristic (AUROC) curve analysis. Results FLI score was associated with NAFLD in multivariable analysis (odds ratio, 1.05; 95% confidence interval CI, 1.04–1.05; P < .001). FLI identified patients with NAFLD with an AUROC curve of 0.813 (95% CI, 0.797–0.830) and those with fatty liver from any cause with an AUROC curve of 0.807 (95% CI, 0.792–0.823). Conclusions The FLI (an algorithm that is based on waist circumference, body mass index, and levels of triglyceride and γ-glutamyltransferase) accurately identifies NAFLD, confirmed via ultrasonography, in a large, white, elderly population.
Exploratory (i.e., voxelwise) spatial methods are commonly used in neuroimaging to identify areas that show an effect when a region-of-interest (ROI) analysis cannot be performed because no strong a ...priori anatomical hypothesis exists. However, noise at a single voxel is much higher than noise in a ROI making noise management critical to successful exploratory analysis. This work explores how preprocessing choices affect the bias and variability of voxelwise kinetic modeling analysis of brain positron emission tomography (PET) data. These choices include the use of volume- or cortical surface-based smoothing, level of smoothing, use of voxelwise partial volume correction (PVC), and PVC masking threshold. PVC was implemented using the Muller-Gartner method with the masking out of voxels with low gray matter (GM) partial volume fraction. Dynamic PET scans of an antagonist serotonin-4 receptor radioligand (11CSB207145) were collected on sixteen healthy subjects using a Siemens HRRT PET scanner. Kinetic modeling was used to compute maps of non-displaceable binding potential (BPND) after preprocessing. The results showed a complicated interaction between smoothing, PVC, and masking on BPND estimates. Volume-based smoothing resulted in large bias and intersubject variance because it smears signal across tissue types. In some cases, PVC with volume smoothing paradoxically caused the estimated BPND to be less than when no PVC was used at all. When applied in the absence of PVC, cortical surface-based smoothing resulted in dramatically less bias and the least variance of the methods tested for smoothing levels 5mm and higher. When used in combination with PVC, surface-based smoothing minimized the bias without significantly increasing the variance. Surface-based smoothing resulted in 2–4 times less intersubject variance than when volume smoothing was used. This translates into more than 4 times fewer subjects needed in a group analysis to achieve similarly powered statistical tests. Surface-based smoothing has less bias and variance because it respects cortical geometry by smoothing the PET data only along the cortical ribbon and so does not contaminate the GM signal with that of white matter and cerebrospinal fluid. The use of surface-based analysis in PET should result in substantial improvements in the reliability and detectability of effects in exploratory PET analysis, with or without PVC.
•This is a study of the effects of preprocessing on exploratory PET analysis.•Volumetric 3D smoothing of PET data exacerbates the partial volume effect.•Volumetric smoothing and partial volume correction combine to increase variability.•Cortical surface-based smoothing does not exacerbate the partial volume effect.•Surface-based kinetic analysis reduces intersubject variance by a factor of 4.
Recent Climate Observations Compared to Projections Rahmstorf, Stefan; Cazenave, Anny; Church, John A ...
Science (American Association for the Advancement of Science),
05/2007, Letnik:
316, Številka:
5825
Journal Article
Recenzirano
Odprti dostop
We present recent observed climate trends for carbon dioxide concentration, global mean air temperature, and global sea level, and we compare these trends to previous model projections as summarized ...in the 2001 assessment report of the Intergovernmental Panel on Climate Change (IPCC). The IPCC scenarios and projections start in the year 1990, which is also the base year of the Kyoto protocol, in which almost all industrialized nations accepted a binding commitment to reduce their greenhouse gas emissions. The data available for the period since 1990 raise concerns that the climate system, in particular sea level, may be responding more quickly to climate change than our current generation of models indicates.
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