4,474 research outputs found
The increasing importance of economic conditions on fertility
No full textThis paper investigates whether there has been a fundamental change in the importance of economic conditions on fertility. Through the 1980s econometric studies had found at best a mixed, neutral or negative effect of economic conditions on fertility. Notably, Butz and Ward (1979) concluded that fertility was counter-cyclical, with fertility falling in good times, as the opportunity costs of childbearing rose. More recently, there have been signs that fluctuations in fertility have been pro-cyclical, with good economic times being associated with higher birth rates, and the recent recession with lower birth rates. In this paper, we use panel methods to study short term changes in aggregate fertility and economic measures in OECD countries from 1976-2008. We find indeed that fertility became positively associated with good economic conditions. Furthermore, the increasing importance of economic conditions was detected for both tempo and quantum.economic conditions, total fertility rate
Inverse relationship between adult hippocampal cell proliferation and synaptic rewiring in the dentate gyrus
No full textButz M, Teuchert-Noodt G, Grafen K, van Ooyen A. Inverse relationship between adult hippocampal cell proliferation and synaptic rewiring in the dentate gyrus. HIPPOCAMPUS. 2008;18(9):879-898.Adult neurogenesis is a key feature of the hippocampal dentate gyrus (DG). Neurogenesis is accompanied by synaptogenesis as new cells become integrated into the circuitry of the hippocampus. However, little is known to what extent the embedding of new neurons rewires the pre-existing network. Here we investigate synaptic rewiring in the DG of gerbils (Meriones unguiculatus) under different rates of adult cell proliferation caused by different rearing conditions as well as juvenile methamphetamine treatment. Surprisingly, we found that an increased cell proliferation reduced the amount of synaptic rewiring. To help explain this unexpected finding, we developed a novel model of dentate network formation incorporating neurogenesis and activity-dependent synapse formation and remodelling. In the model, we show that homeostasis of neuronal activity can account for the inverse relationship between cell proliferation and synaptic rewiring. (C) 2008 Wiley-Liss, Inc
Transgender women of color are more likely to avoid social welfare services and experience discrimination
No full textSocial equity is important in how public services are provided. In new research, using survey data Adam M. Butz and Tia Sherèe Gaynor examine how transgender women of color engage with US social welfare. They find that, compared to other groups, transgender women of color are more likely to avoid seeking welfare services and face discrimination within social welfare offices. Considering these findings, they argue that policymakers and social welfare administrators must pay closer attention to intersectionality and social equity
Gradient descent methods in learning classifier systems: Improving xcs performance in multistep problems
No full textThe accuracy-based XCS classifier system has been shown to solve typical data mining problems in a machine-learning competitive way. However, successful applications in multistep problems, modeled by a Markov decision process, were restricted to very small problems. Until now, the temporal difference learning technique in XCS was based on deterministic updates. However, since a prediction is actually generated by a set of rules in XCS and Learning Classifier Systems in general, gradient-based update methods are applicable. The extension of XCS to gradient-based update methods results in a classifier system that is more robust and more parameter independent, solving large and difficult maze problems reliably. Additionally, the extension to gradient methods highlights the relation of XCS to other function approximation methods in reinforcement learning
Hyper-ellipsoidal conditions in XCS: rotation, linear approximation, and solution structure
No full text
Space Perception through Visuokinesthetic Prediction
No full textSchenck W. Space Perception through Visuokinesthetic Prediction. In: Pezzulo G, Butz M, Sigaud O, Baldassarre G, eds. Anticipatory Behavior in Adaptive Learning Systems: From Psychological Theories to Artificial Cognitive Systems. Lecture Notes in Artificial Intelligence, 5499. Berlin, Heidelberg, New York: Springer; 2009: 247-266
Problem solution sustenance in XCS: Markov chain analysis of niche support distributions and the impact on computational complexity
No full textMichigan-style learning classifier systems iteratively evolve a distributed solution to a problem in the form of potentially overlapping subsolutions. Each problem niche is covered by subsolutions that are represented by a set of predictive rules, termed classifiers. The genetic algorithm is designed to evolve classifier structures that together cover the whole problem space and represent a complete problem solution. An obvious challenge for such an online evolving, distributed knowledge representation is to continuously sustain all problem subsolutions covering all problem niches, that is, to ensure niche support. Effective niche support depends both on the probability of reproduction and on the probability of deletion of classifiers in a niche. In XCS, reproduction is occurrence-based whereas deletion is support-based. In combination, niche support is assured effectively. In this paper we present a Markov chain analysis of the niche support in XCS, which we validate experimentally. Evaluations in diverse Boolean function settings, which require non-overlapping and overlapping solution structures, support the theoretical derivations. We also consider the effects of mutation and crossover on niche support. With respect to computational complexity, the paper shows that XCS is able to maintain (partially overlapping) niches with a computational effort that is linear in the inverse of the niche occurrence frequency
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