State-Observation Sampling and the Econometrics of Learning Models

In nonlinear state-space models, sequential learning about the hidden state can proceed by particle filtering when the density of the observation conditional on the state is available analytically (e.g. Gordon et al., 1993). This condition need not hold in complex environments, such as the incomplete-information equilibrium models considered in financial economics. In this paper, we make two contributions to the learning literature. First, we introduce a new filtering method, the state-observation sampling (SOS) filter, for general state-space models with intractable observation densities. Second, we develop an indirect inference-based estimator for a large class of incomplete-information economies. We demonstrate the good performance of these techniques on an asset pricing model with investor learning applied to over 80 years of daily equity returns

Improving basic and translational science by accounting for litter-to-litter variation in animal models

Background: Animals from the same litter are often more alike compared with animals from different litters. This litter-to-litter variation, or "litter effects", can influence the results in addition to the experimental factors of interest. Furthermore, an experimental treatment can be applied to whole litters rather than to individual offspring. For example, in the valproic acid (VPA) model of autism, VPA is administered to pregnant females thereby inducing the disease phenotype in the offspring. With this type of experiment the sample size is the number of litters and not the total number of offspring. If such experiments are not appropriately designed and analysed, the results can be severely biased as well as extremely underpowered. Results: A review of the VPA literature showed that only 9% (3/34) of studies correctly determined that the experimental unit (n) was the litter and therefore made valid statistical inferences. In addition, litter effects accounted for up to 61% (p <0.001) of the variation in behavioural outcomes, which was larger than the treatment effects. In addition, few studies reported using randomisation (12%) or blinding (18%), and none indicated that a sample size calculation or power analysis had been conducted. Conclusions: Litter effects are common, large, and ignoring them can make replication of findings difficult and can contribute to the low rate of translating preclinical in vivo studies into successful therapies. Only a minority of studies reported using rigorous experimental methods, which is consistent with much of the preclinical in vivo literature.Comment: http://www.biomedcentral.com/1471-2202/14/37/abstrac

A Coverage Criterion for Spaced Seeds and its Applications to Support Vector Machine String Kernels and k-Mer Distances

Spaced seeds have been recently shown to not only detect more alignments, but also to give a more accurate measure of phylogenetic distances (Boden et al., 2013, Horwege et al., 2014, Leimeister et al., 2014), and to provide a lower misclassification rate when used with Support Vector Machines (SVMs) (On-odera and Shibuya, 2013), We confirm by independent experiments these two results, and propose in this article to use a coverage criterion (Benson and Mak, 2008, Martin, 2013, Martin and No{\'e}, 2014), to measure the seed efficiency in both cases in order to design better seed patterns. We show first how this coverage criterion can be directly measured by a full automaton-based approach. We then illustrate how this criterion performs when compared with two other criteria frequently used, namely the single-hit and multiple-hit criteria, through correlation coefficients with the correct classification/the true distance. At the end, for alignment-free distances, we propose an extension by adopting the coverage criterion, show how it performs, and indicate how it can be efficiently computed.Comment: http://online.liebertpub.com/doi/abs/10.1089/cmb.2014.017

Inflation from Supersymmetric Quantum Cosmology

We derive a special scalar field potential using the anisotropic Bianchi type I cosmological model from canonical quantum cosmology under determined conditions in the evolution to anisotropic variables $\beta_\pm$. In the process, we obtain a family of potentials that has been introduced by hand in the literature to explain cosmological data. Considering supersymmetric quantum cosmology, this family is scanned, fixing the exponential potential as more viable in the inflation scenario $\rm V (\phi) = V_0 \,e^{-\sqrt{3}\phi}$.Comment: 14 pages, latex2e, To appear in Phys. Rev.

The question of “evidence” in the emergence of evidence-based or evidence-aware policies in agriculture

Evidence-based or evidence-aware policy approaches are used in many different sectors (health, education, etc.). These approaches are less common in agriculture but are gradually emerging. Analysis of debates surrounding this trend sheds light on the particular nature of the difficulties faced by public decision-makers who are willing to use available scientific knowledge. After examining certain misunderstandings which arise in the international debate over evidence-based policy approaches, this paper addresses two specific issues: (i) the problems of competing evidence for using knowledge in the design of public policies and (ii) the potential role of rationalization tools in a possible "depoliticisation" of public decision-making.knowledge, agriculture, policy, evidence, Agricultural and Food Policy, B29, D8, Q01, O3,

Transformations of agricultural extension services in the EU: Towards a lack of adequate knowledge for small-scale farms

This paper examines the consequences of the transformations of extension services for small scale farms. It presents the results of investigations embedded in regulation theory, which combine a comparative institutional analysis, statistical data processing (national agricultural census) and direct surveys. We describe the transformations in the EU and show that they make it more difficult for small farms to access extension services and to benefit from “front office” support (i.e. direct advice from extensionists). Finally, we emphasize that due to the modification of the knowledge production regime, these small farms may also suffer new specific adverse effects resulting from the re-organization of the "back-office" R&D activities of these extension services (i.e. knowledge base updating, database building, scientific experiments, etc.).Agricultural extension services, Small-scale farms, Institutional Analysis, Europe, Knowledge, Research and Development/Tech Change/Emerging Technologies, Q16, Q12, B52, P51, D83,

Gauge Group TQFT and Improved Perturbative Yang-Mills Theory

We reinterpret the Faddeev-Popov gauge-fixing procedure of Yang-Mills theories as the definition of a topological quantum field theory for gauge group elements depending on a background connection. This has the advantage of relating topological gauge-fixing ambiguities to the global breaking of a supersymmetry. The global zero modes of the Faddeev-Popov ghosts are handled in the context of an equivariant cohomology without breaking translational invariance. The gauge-fixing involves constant fields which play the role of moduli and modify the behavior of Green functions at subasymptotic scales. At the one loop level physical implications from these power corrections are gauge invariant.Comment: 28 pages, uuencoded and compressed tar-file, LATEX+4 PS-figures, uses psfig.sty. New appendix and some clarifying modifications, references adde

Multifrequency Jump-Diffusions: An Equilibrium Approach

This paper proposes that equilibrium valuation is a powerful method to generate endogenous jumps in asset prices, which provides a structural alternative to traditional reduced-form specifications with exogenous discontinuities. We specify an economy with continuous consumption and dividend paths, in which endogenous price jumps originate from the market impact of regime-switches in the drifts and volatilities of fundamentals. We parsimoniously incorporate shocks of heterogeneous durations in consumption and dividends while keeping constant the number of parameters. Equilibrium valuation creates an endogenous relation between a shock's persistence and the magnitude of the induced price jump. As the number of frequencies driving fundamentals goes to infinity, the price process converges to a novel stochastic process, which we call a multifractal jump-diffusion.