848 research outputs found
Symmetric Rank Covariances: a Generalised Framework for Nonparametric Measures of Dependence
The need to test whether two random vectors are independent has spawned a
large number of competing measures of dependence. We are interested in
nonparametric measures that are invariant under strictly increasing
transformations, such as Kendall's tau, Hoeffding's D, and the more recently
discovered Bergsma--Dassios sign covariance. Each of these measures exhibits
symmetries that are not readily apparent from their definitions. Making these
symmetries explicit, we define a new class of multivariate nonparametric
measures of dependence that we refer to as Symmetric Rank Covariances. This new
class generalises all of the above measures and leads naturally to multivariate
extensions of the Bergsma--Dassios sign covariance. Symmetric Rank Covariances
may be estimated unbiasedly using U-statistics for which we prove results on
computational efficiency and large-sample behavior. The algorithms we develop
for their computation include, to the best of our knowledge, the first
efficient algorithms for the well-known Hoeffding's D statistic in the
multivariate setting
Population surveys of Nile crocodiles (Crocodylus niloticus) in the Murchison Falls National Park, Victoria Nile, Uganda
1. A 12-month-long survey (April 2013 to March 2014) for Nile crocodiles (Crocodylus niloticus) was conducted along a section of the Victoria Nile/Ramsar site of Murchison Falls National Park, in order to update the historic information on crocodile populations in the area, locating nesting areas, determining seasonality patterns and habitat use, and assess the current abundance and the population size trends since the 1960s. The methods employed included visual encounter surveys, transect counts and opportunistic methods, by using boats.2. In general, there were diurnal and seasonal fluctuations in the number of crocodile sightings. The crocodile sightings peaked between the months of June and August, with the highest mean number of sightings encountered on any single day being 67 (in July 2013), and the second peak was between January and March with the highest mean of 118 recorded in January 2014. The second peak also coincided with the crocodile breeding season. This clearly shows that the distribution of the sub-population sampled followed a climatic regime.3. Crocodiles were observed most frequently in water (37%). Grassy banks, islands, river mouths and sandy banks constituted about 47% of the habitats utilised by the crocodile population. Although basking was the most frequent type of activity performed by crocodiles (50%) over the entire survey period, their key activities varied significantly from month to month. Nesting was very visible during the last quarter of the year and the first quarter of the New Year.4. There was a clear decline of the abundance of crocodiles in this population between 1960s and nowadays. This declining trend was obvious also taking into account the various survey methodologies employed over the decades
Implicit MLE: Backpropagating Through Discrete Exponential Family Distributions
Combining discrete probability distributions and combinatorial optimization
problems with neural network components has numerous applications but poses
several challenges. We propose Implicit Maximum Likelihood Estimation (I-MLE),
a framework for end-to-end learning of models combining discrete exponential
family distributions and differentiable neural components. I-MLE is widely
applicable as it only requires the ability to compute the most probable states
and does not rely on smooth relaxations. The framework encompasses several
approaches such as perturbation-based implicit differentiation and recent
methods to differentiate through black-box combinatorial solvers. We introduce
a novel class of noise distributions for approximating marginals via
perturb-and-MAP. Moreover, we show that I-MLE simplifies to maximum likelihood
estimation when used in some recently studied learning settings that involve
combinatorial solvers. Experiments on several datasets suggest that I-MLE is
competitive with and often outperforms existing approaches which rely on
problem-specific relaxations.Comment: NeurIPS 2021 camera-ready; repo:
https://github.com/nec-research/tf-iml
Benefits of Enacting and Observing Gestures on Foreign Language Vocabulary Learning : A Systematic Review and Meta-Analysis
Funding S.N. is supported by the German Research Foundation (DFG, Deutsche Forschungsgemeinschaft) as part of Germany’s Excellence Strategy—EXC 2050/1—Project ID 390696704—Cluster of Excellence “Centre for Tactile Internet with Human-in-the-Loop” (CeTI) of Technische Universität Dresden. B.M. is supported by a Research Incentive Grant (RIG)—Project 012506—from the Carnegie Trust for the Universities of Scotland.Peer reviewedPublisher PD
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