11,497 research outputs found
Stock assessment of protogynous fish: evaluating measures of spawning biomass used to estimate biological reference points
In stock assessments, recruitment is typically modeled as a function of females only. For protogynous stocks, however, disproportionate fishing on males increases the possibility of reduced fertilization rates. To incorporate the importance of males in protogynous stocks, assessment models have been used to predict recruitment not just from female spawning biomass (Sf), but also from that of males (Sm) or both sexes (Sb). We conducted a simulation study to evaluate the ability of these three measures to estimate biological reference points used in fishery management. Of the three, Sf provides best estimates if the potential for decreased fertilization is weak, whereas Sm is best only if the potential is very strong. In general, Sb estimates the true reference points most closely, which indicates that if the potential for decreased fertilization is moderate or unknown, Sb should be used in assessments of protogynous stocks. Moreover, for a broad range of scenarios, relative errors from Sf and Sb occur in opposite directions, indicating that estimates from these measures could be used to bound uncertainty
Pessimistic portfolio allocation and Choquet expected utility
Recent developments in the theory of choice under uncertainty and risk yield a pessimistic decision theory that replaces the classical expected utility criterion with a Choquet expectation that accentuates the likelihood of the least favorable outcomes. A parallel theory has recently emerged in the literature on risk assessment. It is shown that a general form of pessimistic portfolio optimization based on the Choquet approach may be formulated as a problem of linear quantile regression.
Density Forecasting: A Survey
A density forecast of the realization of a random variable at some future time is an estimate of the probability distribution of the possible future values of that variable. This article presents a selective survey of applications of density forecasting in macroeconomics and finance, and discusses some issues concerning the production, presentation and evaluation of density forecasts.
A systematic empirical comparison of different approaches for normalizing citation impact indicators
We address the question how citation-based bibliometric indicators can best
be normalized to ensure fair comparisons between publications from different
scientific fields and different years. In a systematic large-scale empirical
analysis, we compare a traditional normalization approach based on a field
classification system with three source normalization approaches. We pay
special attention to the selection of the publications included in the
analysis. Publications in national scientific journals, popular scientific
magazines, and trade magazines are not included. Unlike earlier studies, we use
algorithmically constructed classification systems to evaluate the different
normalization approaches. Our analysis shows that a source normalization
approach based on the recently introduced idea of fractional citation counting
does not perform well. Two other source normalization approaches generally
outperform the classification-system-based normalization approach that we
study. Our analysis therefore offers considerable support for the use of
source-normalized bibliometric indicators
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Recent pace of change in human impact on the world's ocean.
Humans interact with the oceans in diverse and profound ways. The scope, magnitude, footprint and ultimate cumulative impacts of human activities can threaten ocean ecosystems and have changed over time, resulting in new challenges and threats to marine ecosystems. A fundamental gap in understanding how humanity is affecting the oceans is our limited knowledge about the pace of change in cumulative impact on ocean ecosystems from expanding human activities - and the patterns, locations and drivers of most significant change. To help address this, we combined high resolution, annual data on the intensity of 14 human stressors and their impact on 21 marine ecosystems over 11 years (2003-2013) to assess pace of change in cumulative impacts on global oceans, where and how much that pace differs across the ocean, and which stressors and their impacts contribute most to those changes. We found that most of the ocean (59%) is experiencing significantly increasing cumulative impact, in particular due to climate change but also from fishing, land-based pollution and shipping. Nearly all countries saw increases in cumulative impacts in their coastal waters, as did all ecosystems, with coral reefs, seagrasses and mangroves at most risk. Mitigation of stressors most contributing to increases in overall cumulative impacts is urgently needed to sustain healthy oceans
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