881 research outputs found
Can groups improve expert economic and financial forecasts?
Economic and financial forecasts are important for business planning and government policy but are notoriously challenging. We take advantage of recent advances in individual and group judgement, and a data set of economic and financial forecasts compiled over 25 years, consisting of multiple individual and institutional estimates, to test the claim that nominal groups will make more accurate economic and financial forecast than individuals. We validate the forecasts using the subsequent published (real) outcomes, explore the performance of nominal groups against institutions, identify potential superforecasters and discuss the benefits of implementing structured judgment techniques to improve economic and financial forecasts
Improving expert forecasts in reliability. Application and evidence for structured elicitation protocols
Quantitative expert judgementsare used in reliability assessmentsto informcritically important decisions. Structured elicitation protocols have been advocated to improveexpert judgements, yet their application in reliability ischallenged by a lack of examples or evidence that they improve judgements. This paper aims to overcome these barriers. We present a case study where two world-leading protocols, the IDEA protocol and the Classical Model were combined and applied by the Australian Department of Defence for a reliability assessment. We assess the practicality of the methods, and the extent to which they improve judgements. The average expert was extremely overconfident, with 90% credible intervals containing the true realisation 36% of the time. However,steps contained inthe protocols substantially improvedjudgements. In particular, an equal weighted aggregation of individual judgements, and the inclusion ofa discussion phase and revised estimate helped to improve calibration, statistical accuracy and the Classical Model score. Further improvements in precision and information were made via performance weighted aggregation. This paper provides useful insights into the application of structured elicitation protocols for reliability andthe extent to which judgements are improved. The findings raise concerns about existing practices for utilising experts in reliability assessments and suggest greater adoption of structured protocols is warranted. We encourage the reliability community to further develop examples and insights
The value of performance weights and discussion in aggregated expert judgements
In risky situations characterized by imminent decisions, scarce resources, and insufficient data, policymakers rely on experts to estimate model parameters and their associated uncertainties. Different elicitation and aggregation methods can vary substantially in their efficacy and robustness. While it is generally agreed that biases in expert judgments can be mitigated using structured elicitations involving groups rather than individuals, there is still some disagreement about how to best elicit and aggregate judgments. This mostly concerns the merits of using performanceâbased weighting schemes to combine judgments of different individuals (rather than assigning equal weights to individual experts), and the way that interaction between experts should be handled. This article aims to contribute to, and complement, the ongoing discussion on these topics
Robust decision-making under severe uncertainty for conservation management
In-conservation biology it is necessary to make management decisions for endangered and threatened species under severe uncertainty. Failure to acknowledge and treat uncertainty can lead to poor decisions. To illustrate the importance of considering uncertainty, we reanalyze a decision problem for the Sumatran rhino, Dicerorhinus sumatrensis, using information-gap theory to propagate uncertainties and to rank management options. Rather than requiring information about the extent of parameter uncertainty at the outset, information-gap theory addresses the question of how much uncertainty can be tolerated before our decision would change. It assesses the robustness of decisions in the face of severe uncertainty. We show that different management decisions may result when uncertainty in utilities and probabilities are considered in decision-making problems. We highlight the importance of a full assessment of uncertainty in conservation management decisions to avoid, as much as possible, undesirable outcomes
The contribution of Fermi-2LAC blazars to the diffuse TeV-PeV neutrino flux
The recent discovery of a diffuse cosmic neutrino flux extending up to PeV
energies raises the question of which astrophysical sources generate this
signal. One class of extragalactic sources which may produce such high-energy
neutrinos are blazars. We present a likelihood analysis searching for
cumulative neutrino emission from blazars in the 2nd Fermi-LAT AGN catalogue
(2LAC) using an IceCube neutrino dataset 2009-12 which was optimised for the
detection of individual sources. In contrast to previous searches with IceCube,
the populations investigated contain up to hundreds of sources, the largest one
being the entire blazar sample in the 2LAC catalogue. No significant excess is
observed and upper limits for the cumulative flux from these populations are
obtained. These constrain the maximum contribution of the 2LAC blazars to the
observed astrophysical neutrino flux to be or less between around 10
TeV and 2 PeV, assuming equipartition of flavours at Earth and a single
power-law spectrum with a spectral index of . We can still exclude that
the 2LAC blazars (and sub-populations) emit more than of the observed
neutrinos up to a spectral index as hard as in the same energy range.
Our result takes into account that the neutrino source count distribution is
unknown, and it does not assume strict proportionality of the neutrino flux to
the measured 2LAC -ray signal for each source. Additionally, we
constrain recent models for neutrino emission by blazars.Comment: 18 pages, 22 figure
Lowering IceCubeâs energy threshold for point source searches in the southern sky
Observation of a point source of astrophysical neutrinos would be a "smoking gun" signature of a cosmic-ray accelerator. While IceCube has recently discovered a diffuse flux of astrophysical neutrinos, no localized point source has been observed. Previous IceCube searches for point sources in the southern sky were restricted by either an energy threshold above a few hundred TeV or poor neutrino angular resolution. Here we present a search for southern sky point sources with greatly improved sensitivities to neutrinos with energies below 100 TeV. By selecting charged-current nu(mu) interacting inside the detector, we reduce the atmospheric background while retaining efficiency for astrophysical neutrino-induced events reconstructed with sub-degree angular resolution. The new event sample covers three years of detector data and leads to a factor of 10 improvement in sensitivity to point sources emitting below 100 TeV in the southern sky. No statistically significant evidence of point sources was found, and upper limits are set on neutrino emission from individual sources. A posteriori analysis of the highest-energy (similar to 100 TeV) starting event in the sample found that this event alone represents a 2.8 sigma deviation from the hypothesis that the data consists only of atmospheric background
Observation and Characterization of a Cosmic Muon Neutrino Flux from the Northern Hemisphere using six years of IceCube data
The IceCube Collaboration has previously discovered a high-energy
astrophysical neutrino flux using neutrino events with interaction vertices
contained within the instrumented volume of the IceCube detector. We present a
complementary measurement using charged current muon neutrino events where the
interaction vertex can be outside this volume. As a consequence of the large
muon range the effective area is significantly larger but the field of view is
restricted to the Northern Hemisphere. IceCube data from 2009 through 2015 have
been analyzed using a likelihood approach based on the reconstructed muon
energy and zenith angle. At the highest neutrino energies between 191 TeV and
8.3 PeV a significant astrophysical contribution is observed, excluding a
purely atmospheric origin of these events at significance. The
data are well described by an isotropic, unbroken power law flux with a
normalization at 100 TeV neutrino energy of
and a hard spectral index of . The observed spectrum is
harder in comparison to previous IceCube analyses with lower energy thresholds
which may indicate a break in the astrophysical neutrino spectrum of unknown
origin. The highest energy event observed has a reconstructed muon energy of
which implies a probability of less than 0.005% for
this event to be of atmospheric origin. Analyzing the arrival directions of all
events with reconstructed muon energies above 200 TeV no correlation with known
-ray sources was found. Using the high statistics of atmospheric
neutrinos we report the currently best constraints on a prompt atmospheric muon
neutrino flux originating from charmed meson decays which is below in
units of the flux normalization of the model in Enberg et al. (2008).Comment: 20 pages, 21 figure
All-sky search for time-integrated neutrino emission from astrophysical sources with 7 years of IceCube data
Since the recent detection of an astrophysical flux of high energy neutrinos,
the question of its origin has not yet fully been answered. Much of what is
known about this flux comes from a small event sample of high neutrino purity,
good energy resolution, but large angular uncertainties. In searches for
point-like sources, on the other hand, the best performance is given by using
large statistics and good angular reconstructions. Track-like muon events
produced in neutrino interactions satisfy these requirements. We present here
the results of searches for point-like sources with neutrinos using data
acquired by the IceCube detector over seven years from 2008--2015. The
discovery potential of the analysis in the northern sky is now significantly
below , on average
lower than the sensitivity of the previously published analysis of four
years exposure. No significant clustering of neutrinos above background
expectation was observed, and implications for prominent neutrino source
candidates are discussed.Comment: 19 pages, 17 figures, 3 tables; ; submitted to The Astrophysical
Journa
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