Pembroke College

Oxford, United Kingdom

Pembroke College

Oxford, United Kingdom
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Machete R.L.,Botswana Institute for Technology Research and Innovation | Machete R.L.,The London School of Economics and Political Science | Smith L.A.,The London School of Economics and Political Science | Smith L.A.,Pembroke College
Tellus, Series A: Dynamic Meteorology and Oceanography | Year: 2016

Ensemble simulation propagates a collection of initial states forward in time in a Monte Carlo fashion. Depending on the fidelity of the model and the properties of the initial ensemble, the goal of ensemble simulation can range from merely quantifying variations in the sensitivity of the model all the way to providing actionable probability forecasts of the future. Whatever the goal is, success depends on the properties of the ensemble, and there is a longstanding discussion in meteorology as to the size of initial condition ensemble most appropriate for Numerical Weather Prediction. In terms of resource allocation: how is one to divide finite computing resources between model complexity, ensemble size, data assimilation and other components of the forecast system. One wishes to avoid undersampling information available from the model's dynamics, yet one also wishes to use the highest fidelity model available. Arguably, a higher fidelity model can better exploit a larger ensemble; nevertheless it is often suggested that a relatively small ensemble, say ~16 members, is sufficient and that larger ensembles are not an effective investment of resources. This claim is shown to be dubious when the goal is probabilistic forecasting, even in settings where the forecast model is informative but imperfect. Probability forecasts for a 'simple' physical system are evaluated at different lead times; ensembles of up to 256 members are considered. The pure density estimation context (where ensemble members are drawn from the same underlying distribution as the target) differs from the forecasting context, where one is given a high fidelity (but imperfect) model. In the forecasting context, the information provided by additional members depends also on the fidelity of the model, the ensemble formation scheme (data assimilation), the ensemble interpretation and the nature of the observational noise. The effect of increasing the ensemble size is quantified by its relative information content (in bits) using a proper skill score. Doubling the ensemble size is demonstrated to yield a non-trivial increase in the information content (forecast skill) for an ensemble with well over 16 members; this result stands in forecasting a mathematical system and a physical system. Indeed, even at the largest ensemble sizes considered (128 and 256), there are lead times where the forecast information is still increasing with ensemble size. Ultimately, model error will limit the value of ever larger ensembles. No support is found, however, for limiting design studies to the sizes commonly found in seasonal and climate studies. It is suggested that ensemble size be considered more explicitly in future design studies of forecast systems on all time scales. © 2016 R. L. Machete and L. A. Smith.


Cobham D.,Heriot - Watt University | Adam C.,St Cross College | Mayhew K.,Pembroke College
Oxford Review of Economic Policy | Year: 2013

We consider the economic record of the 1997-2010 Labour government in the UK. Following a brief review of the government's inheritance from its predecessor, we review the assessments made in the other papers in this issue of the Oxford Review of Economic Policy: the change in the macroeconomic policy framework (which apparently worked well for a decade but was then struck by the global financial crisis); labour market, social security, and education policies and inequality; public investment and public service delivery (especially health); and corporate taxation. We discuss the constraints under which the government operated, how much it broke with the past, and the new frameworks it introduced. We identify strengths and weaknesses and draw lessons from the government's record about the need to remain receptive to other and critical ideas, on the one hand, and the need for Labour to spell out the kind of economy and society it wants to see develop, on the other. © The Authors 2013. Published by Oxford University Press.


Du H.,Center for the Analysis of Time Series | Smith L.A.,Center for the Analysis of Time Series | Smith L.A.,Pembroke College
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2012

Dynamical modeling lies at the heart of our understanding of physical systems. Its role in science is deeper than mere operational forecasting, in that it allows us to evaluate the adequacy of the mathematical structure of our models. Despite the importance of model parameters, there is no general method of parameter estimation outside linear systems. A relatively simple method of parameter estimation for nonlinear systems is introduced, based on variations in the accuracy of probability forecasts. It is illustrated on the logistic map, the Henon map, and the 12-dimensional Lorenz96 flow, and its ability to outperform linear least squares in these systems is explored at various noise levels and sampling rates. As expected, it is more effective when the forecast error distributions are non-Gaussian. The method selects parameter values by minimizing a proper, local skill score for continuous probability forecasts as a function of the parameter values. This approach is easier to implement in practice than alternative nonlinear methods based on the geometry of attractors or the ability of the model to shadow the observations. Direct measures of inadequacy in the model, the "implied ignorance," and the information deficit are introduced. © 2012 American Physical Society.


Smith L.A.,Center for the Analysis of Time Series | Smith L.A.,Center for Climate Change Economics and Policy | Smith L.A.,Pembroke College | Stern N.,Center for Climate Change Economics and Policy
Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences | Year: 2011

Policy-making is usually about risk management. Thus, the handling of uncertainty in science is central to its support of sound policy-making. There is value in scientists engaging in a deep conversation with policy-makers and others, not merely 'delivering' results or analyses and then playing no further role. Communicating the policy relevance of different varieties of uncertainty, including imprecision, ambiguity, intractability and indeterminism, is an important part of this conversation. Uncertainty is handled better when scientists engage with policy-makers. Climate policy aims both to alter future risks (particularly via mitigation) and to take account of and respond to relevant remaining risks (via adaptation) in the complex causal chain that begins and ends with individuals. Policy-making profits from learning how to shift the distribution of risks towards less dangerous impacts, even if the probability of events remains uncertain. Immediate value lies not only in communicating how risks may change with time and how those risks may be changed by action, but also in projecting how our understanding of those risks may improve with time (via science) and how our ability to influence them may advance (via technology and policy design). Guidance on the most urgent places to gather information and realistic estimates of when to expect more informative answers is of immediate value, as are plausible estimates of the risk of delaying action. Risk assessment requires grappling with probability and ambiguity (uncertainty in the Knightian sense) and assessing the ethical, logical, philosophical and economic underpinnings of whether a target of '50 per cent chance of remaining under +2°C' is either 'right' or 'safe'. How do we better stimulate advances in the difficult analytical and philosophical questions while maintaining foundational scientific work advancing our understanding of the phenomena? And provide immediate help with decisions that must be made now? This journal is © 2011 The Royal Society.


Smith L.A.,Center for the Analysis of Time Series | Smith L.A.,Pembroke College | Du H.,Center for the Analysis of Time Series | Suckling E.B.,Center for the Analysis of Time Series | Niehorster F.,Center for the Analysis of Time Series
Quarterly Journal of the Royal Meteorological Society | Year: 2015

Simulation models are widely employed to make probability forecasts of future conditions on seasonal to annual lead times. Added value in such forecasts is reflected in the information they add, either to purely empirical statistical models or to simpler simulation models. An evaluation of seasonal probability forecasts from the Development of a European Multimodel Ensemble system for seasonal to inTERannual prediction (DEMETER) and ENSEMBLES multi-model ensemble experiments is presented. Two particular regions are considered: Nino3.4 in the Pacific and the Main Development Region in the Atlantic; these regions were chosen before any spatial distribution of skill was examined. The ENSEMBLES models are found to have skill against the climatological distribution on seasonal time-scales. For models in ENSEMBLES that have a clearly defined predecessor model in DEMETER, the improvement from DEMETER to ENSEMBLES is discussed. Due to the long lead times of the forecasts and the evolution of observation technology, the forecast-outcome archive for seasonal forecast evaluation is small; arguably, evaluation data for seasonal forecasting will always be precious. Issues of information contamination from in-sample evaluation are discussed and impacts (both positive and negative) of variations in cross-validation protocol are demonstrated. Other difficulties due to the small forecast-outcome archive are identified. The claim that the multi-model ensemble provides a 'better' probability forecast than the best single model is examined and challenged. Significant forecast information beyond the climatological distribution is also demonstrated in a persistence probability forecast. The ENSEMBLES probability forecasts add significantly more information to empirical probability forecasts on seasonal time-scales than on decadal scales. Current operational forecasts might be enhanced by melding information from both simulation models and empirical models. Simulation models based on physical principles are sometimes expected, in principle, to outperform empirical models; direct comparison of their forecast skill provides information on progress toward that goal. © 2014 The Authors.


Amable B.,Institut Universitaire de France | Mayhew K.,Pembroke College
Oxford Review of Economic Policy | Year: 2011

This article examines the course of unemployment in OECD countries during the recent recession. The severity of the recession and the strength of macro policy responses varied from country to country. However, even after correcting for these differences, unemployment experiences were various. Unemployment generally rose by less in those countries which had strict employment protection legislation, as it did in those countries with relatively high collective-bargaining coverage. Various forms of work-sharing also helped some countries to dampen the rise in unemployment. So did increasing the generosity of out-ofwork benefit arrangements. The latter finding suggests that search theoretic approaches need to be modified. Institutions do matter and not just in the short run. Hysteresis effects could project their influence into the medium term. © The Authors 2011. Published by Oxford University Press.


Verma R.,University of Lucknow | Varatharaj A.,Pembroke College
Epilepsy and Behavior | Year: 2011

Dengue fever is becoming a great public health problem leading to significant morbidity and mortality, particularly in developing countries. In the past few years, various neurological complications have been reported globally. Dengue encephalitis as a clinical presentation of dengue fever is now gaining recognition in the scientific community. It is characterized by fever, headache, reduced consciousness, and generalized seizures. Epilepsia partialis continua, a type of focal status epilepticus, is caused by multiple clinical disorders, including viral encephalitis. We describe a young woman who manifested epilepsia partialis continua caused by dengue encephalitis. © 2010 Elsevier Inc.


Mayhew K.,Pembroke College
Oxford Review of Economic Policy | Year: 2015

This article considers the evolution of UK labour market policy during the last 30 years. It does this through the lens of the 'social model'. The social model encompasses the employment relations system, the social welfare system, and the education and training system. It was changed dramatically by the Thatcher and Major governments. The succeeding Labour and Coalition governments largely embraced this new model and, in some ways, increased the pace of change. The consequences for labour market performance-employment, unemployment, productivity, and inequality-are explored. © The Author 2015.


Holmes C.,Pembroke College | Mayhew K.,Pembroke College
Oxford Review of Economic Policy | Year: 2016

This paper describes the expansion of higher education (HE) in OECD countries and discusses its economic consequences. For most governments this expansion has been seen as the silver bullet that improves economic growth and helps tackle problems of inequality. However, in most countries increasing numbers of graduates are going into jobs that were once done by non-graduates, raising the concern that the true social returns to HE expansion are low. Because of this it is unsurprising that economists have found it difficult to establish firm links between higher education expansion and economic growth. At the same time, in some countries, HE expansion has exacerbated problems of economic and social inequality. The paper argues that governments need to take a more realistic view of the role of HE, consider alternative ways of preparing people for the labour market, and at the same time explore more rigorously exactly how the sector is conducting itself. © The Authors 2016. Published by Oxford University Press.


PubMed | Pembroke College
Type: | Journal: Journal of the history of medicine and allied sciences | Year: 2016

The article examines the establishment and growth between 1793 and 1802 of the West India Regiments, British army corps manned by slaves of African descent and commanded by European officers. Focusing on the medical history of British military operations in the West Indies, the article demonstrates that the rationale behind the regiments was medical, but that the impetus for them came from senior military commanders rather than from the medical practitioners whose writings are usually privileged in the historiography. The senior officers who commanded the West Indian expeditions in the French Revolutionary Wars mobilized their own particular brand of medical theory, based explicitly on their experience of the regions epidemiological environment, in support of the policy. This willingness to adopt and adapt medical ideas heavily influenced both military policy regarding the regiments, and commanders relationships with their medical men.

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