10,133 research outputs found
Bayesian model selection in logistic regression for the detection of adverse drug reactions
Motivation: Spontaneous adverse event reports have a high potential for
detecting adverse drug reactions. However, due to their dimension, exploring
such databases requires statistical methods. In this context,
disproportionality measures are used. However, by projecting the data onto
contingency tables, these methods become sensitive to the problem of
co-prescriptions and masking effects. Recently, logistic regressions have been
used with a Lasso type penalty to perform the detection of associations between
drugs and adverse events. However, the choice of the penalty value is open to
criticism while it strongly influences the results. Results: In this paper, we
propose to use a logistic regression whose sparsity is viewed as a model
selection challenge. Since the model space is huge, a Metropolis-Hastings
algorithm carries out the model selection by maximizing the BIC criterion.
Thus, we avoid the calibration of penalty or threshold. During our application
on the French pharmacovigilance database, the proposed method is compared to
well established approaches on a reference data set, and obtains better rates
of positive and negative controls. However, many signals are not detected by
the proposed method. So, we conclude that this method should be used in
parallel to existing measures in pharmacovigilance.Comment: 7 pages, 3 figures, submitted to Biometrical Journa
A Bayesian Periodogram Finds Evidence for Three Planets in 47 Ursae Majoris
A Bayesian analysis of 47 Ursae Majoris (47 UMa) radial velocity data
confirms and refines the properties of two previously reported planets with
periods of 1079 and 2325 days and finds evidence for an additional long period
planet with a period of approximately 10000 days. The three planet model is
found to be 10^5 times more probable than the next most probable model which is
a two planet model. The nonlinear model fitting is accomplished with a new
hybrid Markov chain Monte Carlo (HMCMC) algorithm which incorporates parallel
tempering, simulated annealing and genetic crossover operations. Each of these
features facilitate the detection of a global minimum in chi-squared. By
combining all three, the HMCMC greatly increases the probability of realizing
this goal. When applied to the Kepler problem it acts as a powerful
multi-planet Kepler periodogram. The measured periods are 1078 \pm 2,
2391{+100}{-87}, and 14002{+4018}{-5095}d, and the corresponding eccentricities
are 0.032 \pm 0.014, 0.098{+.047}{-.096}, and 0.16{+.09}{-.16}. The results
favor low eccentricity orbits for all three. Assuming the three signals (each
one consistent with a Keplerian orbit) are caused by planets, the corresponding
limits on planetary mass (M sin i) and semi-major axis are (2.53{+.07}{-.06}MJ,
2.10\pm0.02au), (0.54\pm0.07MJ, 3.6\pm0.1au), and (1.6{+0.3}{-0.5}MJ,
11.6{+2.1}{-2.9}au), respectively. We have also characterized a noise induced
eccentricity bias and designed a correction filter that can be used as an
alternate prior for eccentricity, to enhance the detection of planetary orbits
of low or moderate eccentricity
Sequentiality and Adaptivity Gains in Active Hypothesis Testing
Consider a decision maker who is responsible to collect observations so as to
enhance his information in a speedy manner about an underlying phenomena of
interest. The policies under which the decision maker selects sensing actions
can be categorized based on the following two factors: i) sequential vs.
non-sequential; ii) adaptive vs. non-adaptive. Non-sequential policies collect
a fixed number of observation samples and make the final decision afterwards;
while under sequential policies, the sample size is not known initially and is
determined by the observation outcomes. Under adaptive policies, the decision
maker relies on the previous collected samples to select the next sensing
action; while under non-adaptive policies, the actions are selected independent
of the past observation outcomes.
In this paper, performance bounds are provided for the policies in each
category. Using these bounds, sequentiality gain and adaptivity gain, i.e., the
gains of sequential and adaptive selection of actions are characterized.Comment: 12 double-column pages, 1 figur
Equivalent efficiency of a simulated photon-number detector
Homodyne detection is considered as a way to improve the efficiency of
communication near the single-photon level. The current lack of commercially
available {\it infrared} photon-number detectors significantly reduces the
mutual information accessible in such a communication channel. We consider
simulating direct detection via homodyne detection. We find that our particular
simulated direct detection strategy could provide limited improvement in the
classical information transfer. However, we argue that homodyne detectors (and
a polynomial number of linear optical elements) cannot simulate photocounters
arbitrarily well, since otherwise the exponential gap between quantum and
classical computers would vanish.Comment: 4 pages, 4 figure
Context-Aware Generative Adversarial Privacy
Preserving the utility of published datasets while simultaneously providing
provable privacy guarantees is a well-known challenge. On the one hand,
context-free privacy solutions, such as differential privacy, provide strong
privacy guarantees, but often lead to a significant reduction in utility. On
the other hand, context-aware privacy solutions, such as information theoretic
privacy, achieve an improved privacy-utility tradeoff, but assume that the data
holder has access to dataset statistics. We circumvent these limitations by
introducing a novel context-aware privacy framework called generative
adversarial privacy (GAP). GAP leverages recent advancements in generative
adversarial networks (GANs) to allow the data holder to learn privatization
schemes from the dataset itself. Under GAP, learning the privacy mechanism is
formulated as a constrained minimax game between two players: a privatizer that
sanitizes the dataset in a way that limits the risk of inference attacks on the
individuals' private variables, and an adversary that tries to infer the
private variables from the sanitized dataset. To evaluate GAP's performance, we
investigate two simple (yet canonical) statistical dataset models: (a) the
binary data model, and (b) the binary Gaussian mixture model. For both models,
we derive game-theoretically optimal minimax privacy mechanisms, and show that
the privacy mechanisms learned from data (in a generative adversarial fashion)
match the theoretically optimal ones. This demonstrates that our framework can
be easily applied in practice, even in the absence of dataset statistics.Comment: Improved version of a paper accepted by Entropy Journal, Special
Issue on Information Theory in Machine Learning and Data Scienc
Detection of exomoons in simulated light curves with a regularized convolutional neural network
Many moons have been detected around planets in our Solar System, but none
has been detected unambiguously around any of the confirmed extrasolar planets.
We test the feasibility of a supervised convolutional neural network to
classify photometric transit light curves of planet-host stars and identify
exomoon transits, while avoiding false positives caused by stellar variability
or instrumental noise. Convolutional neural networks are known to have
contributed to improving the accuracy of classification tasks. The network
optimization is typically performed without studying the effect of noise on the
training process. Here we design and optimize a 1D convolutional neural network
to classify photometric transit light curves. We regularize the network by the
total variation loss in order to remove unwanted variations in the data
features. Using numerical experiments, we demonstrate the benefits of our
network, which produces results comparable to or better than the standard
network solutions. Most importantly, our network clearly outperforms a
classical method used in exoplanet science to identify moon-like signals. Thus
the proposed network is a promising approach for analyzing real transit light
curves in the future
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