64 research outputs found

    The vector innovation structural time series framework: a simple approach to multivariate forecasting

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    The vector innovation structural time series framework is proposed as a way of modelling a set of related time series. Like all multi-series approaches, the aim is to exploit potential inter-series dependencies to improve the fit and forecasts. A key feature of the framework is that the series are decomposed into common components such as trend and seasonal effects. Equations that describe the evolution of these components through time are used as the sole way of representing the inter-temporal dependencies. The approach is illustrated on a bivariate data set comprising Australian exchange rates of the UK pound and US dollar. Its forecasting capacity is compared to other common single- and multi-series approaches in an experiment using time series from a large macroeconomic database.Vector innovation structural time series, state space model, multivariate time series, exponential smoothing, forecast comparison, vector autoregression.

    Making a U-turn on the Purfleet Interchange: Stone Tool Technology in Marine Isotope Stage 9 Britain and the Emergence of the Middle Palaeolithic in Europe

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    This paper re-examines earlier Palaeolithic core technology from British sites assigned to MIS 11, 9, and 7 using primarily a châine opératoire approach, with the objective of better understanding the earliest occurrence and distribution of Levallois and other prepared-core technologies across the Old World. Contrary to previous interpretations (White and Ashton in Current Anthropology, 44: 598–609, 2003), we find no evidence for a true Levallois concept in MIS 11 or MIS 9 in Britain. Cores previously described as ‘simple prepared cores’ or ‘proto-Levallois’ cores show neither evidence of core management nor predetermination of the resulting flakes. They can instead be explained as the coincidental result of a simpler technological scheme aimed at exploiting the largest surface area of a core, thereby maximising the size of the flakes produced from it. This may be a more widespread practice, or a local solution derived from existing principles. Levallois appears fully formed in Britain during terminal MIS 8/initial MIS 7. Consequently, Britain does not provide evidence for an in situ evolution of Levallois, rather we argue it was introduced by new settlers after a glacial abandonment: the solution to the emergence and significance of Levallois lies in southern Europe, the Levant and Africa

    C-Field Methods for Non-Equilibrium Bose Gases

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    We review c-field methods for simulating the non-equilibrium dynamics of degenerate Bose gases beyond the mean-field Gross-Pitaevskii approximation. We describe three separate approaches that utilise similar numerical methods, but have distinct regimes of validity. Systems at finite temperature can be treated with either the closed-system projected Gross-Pitaevskii equation (PGPE), or the open-system stochastic projected Gross-Pitaevskii equation (SPGPE). These are both applicable in quantum degenerate regimes in which thermal fluctuations are significant. At low or zero temperature, the truncated Wigner projected Gross-Pitaevskii equation (TWPGPE) allows for the simulation of systems in which spontaneous collision processes seeded by quantum fluctuations are important. We describe the regimes of validity of each of these methods, and discuss their relationships to one another, and to other simulation techniques for the dynamics of Bose gases. The utility of the SPGPE formalism in modelling non-equilibrium Bose gases is illustrated by its application to the dynamics of spontaneous vortex formation in the growth of a Bose-Einstein condensate.Comment: 7 pages, 1 figure. Unedited version of chapter to appear in Quantum Gases: Finite Temperature and Non-Equilibrium Dynamics (Vol. 1 Cold Atoms Series). N.P. Proukakis, S.A. Gardiner, M.J. Davis and M.H. Szymanska, eds. Imperial College Press, London (in press). See http://www.icpress.co.uk/physics/p817.html v2: Added arXiv cross-reference

    Ladies in waiting: the timeliness of first trimester services in New Zealand

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    <p>Abstract</p> <p>Background</p> <p>Termination of pregnancy (TOP) services are a core service in New Zealand. However, compared to other developed countries, TOP services are accessed significantly later in the first trimester, increasing the risk for complications. The aim of this study is to examine the timeliness of access to first trimester TOP services and establish the length of delay between different points in the care pathway for these services.</p> <p>Methodology</p> <p>Data were collected from all patients attending nine TOP clinics around the country between February and May 2009 (N = 2950). Patient records were audited to determine the timeline between the first point of entry to the health system to the date of termination. In addition, women were invited to fill out a questionnaire to identify personal level factors affecting access to services (N = 1086, response rate = 36.8%).</p> <p>Results</p> <p>Women waited an average of almost 25 days between the date of the first visit with the referring doctor and the date of their termination procedure. There was a delay of 10 days between the first visit with the referring doctor and the date that the appointment for the procedure was booked, and a further 10 days delay between the date the appointment was booked and the first appointment date. Over half of the women in this study had their pregnancy terminated at ten weeks or above.</p> <p>Conclusion</p> <p>Women in New Zealand are subject to a lengthy delay while seeking TOP services. Efforts should be made by TOP clinics as well as referring doctors to reduce the waiting times for this service.</p

    Naomi: a new modelling tool for estimating HIV epidemic indicators at the district level in sub-Saharan Africa.

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    INTRODUCTION: HIV planning requires granular estimates for the number of people living with HIV (PLHIV), antiretroviral treatment (ART) coverage and unmet need, and new HIV infections by district, or equivalent subnational administrative level. We developed a Bayesian small-area estimation model, called Naomi, to estimate these quantities stratified by subnational administrative units, sex, and five-year age groups. METHODS: Small-area regressions for HIV prevalence, ART coverage and HIV incidence were jointly calibrated using subnational household survey data on all three indicators, routine antenatal service delivery data on HIV prevalence and ART coverage among pregnant women, and service delivery data on the number of PLHIV receiving ART. Incidence was modelled by district-level HIV prevalence and ART coverage. Model outputs of counts and rates for each indicator were aggregated to multiple geographic and demographic stratifications of interest. The model was estimated in an empirical Bayes framework, furnishing probabilistic uncertainty ranges for all output indicators. Example results were presented using data from Malawi during 2016-2018. RESULTS: Adult HIV prevalence in September 2018 ranged from 3.2% to 17.1% across Malawi's districts and was higher in southern districts and in metropolitan areas. ART coverage was more homogenous, ranging from 75% to 82%. The largest number of PLHIV was among ages 35 to 39 for both women and men, while the most untreated PLHIV were among ages 25 to 29 for women and 30 to 34 for men. Relative uncertainty was larger for the untreated PLHIV than the number on ART or total PLHIV. Among clients receiving ART at facilities in Lilongwe city, an estimated 71% (95% CI, 61% to 79%) resided in Lilongwe city, 20% (14% to 27%) in Lilongwe district outside the metropolis, and 9% (6% to 12%) in neighbouring Dowa district. Thirty-eight percent (26% to 50%) of Lilongwe rural residents and 39% (27% to 50%) of Dowa residents received treatment at facilities in Lilongwe city. CONCLUSIONS: The Naomi model synthesizes multiple subnational data sources to furnish estimates of key indicators for HIV programme planning, resource allocation, and target setting. Further model development to meet evolving HIV policy priorities and programme need should be accompanied by continued strengthening and understanding of routine health system data
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