131,443 research outputs found
Financial predictions using cost sensitive neural networks for multi-class learning
The interest in the localisation of wireless sensor networks has grown in recent years. A variety of machine-learning methods have been proposed in recent years to improve the optimisation of the complex behaviour of wireless networks. Network administrators have found that traditional classification algorithms may be limited with imbalanced datasets. In fact, the problem of imbalanced data learning has received particular interest. The purpose of this study was to examine design modifications to neural networks in order to address the problem of cost optimisation decisions and financial predictions. The goal was to compare four learning-based techniques using cost-sensitive neural network ensemble for multiclass imbalance data learning. The problem is formulated as a combinatorial cost optimisation in terms of minimising the cost using meta-learning classification rules for NaiÌve Bayes, J48, Multilayer Perceptions, and Radial Basis Function models. With these models, optimisation faults and cost evaluations for network training are considered
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When the machine does not know measuring uncertainty in deep learning models of medical images
This thesis was submitted for the award of Doctor of Philosophy and was awarded by Brunel University LondonRecently, Deep learning (DL), which involves powerful black box predictors, has outperformed
human experts in several medical diagnostic problems. However, these methods focus
exclusively on improving the accuracy of point predictions without assessing their outputsâ
quality and ignore the asymmetric cost involved in different types of misclassification errors.
Neural networks also do not deliver confidence in predictions and suffer from over and
under confidence, i.e. are not well calibrated. Knowing how much confidence there is in a
prediction is essential for gaining cliniciansâ trust in the technology.
Calibrated uncertainty quantification is a challenging problem as no ground truth is
available. To address this, we make two observations: (i) cost-sensitive deep neural networks
with Dropweights models better quantify calibrated predictive uncertainty, and (ii) estimated
uncertainty with point predictions in Deep Ensembles Bayesian Neural Networks with
DropWeights can lead to a more informed decision and improve prediction quality.
This dissertation focuses on quantifying uncertainty using concepts from cost-sensitive
neural networks, calibration of confidence, and Dropweights ensemble method. First, we
show how to improve predictive uncertainty by deep ensembles of neural networks with Dropweights
learning an approximate distribution over its weights in medical image segmentation
and its application in active learning. Second, we use the Jackknife resampling technique
to correct bias in quantified uncertainty in image classification and propose metrics to measure
uncertainty performance. The third part of the thesis is motivated by the discrepancy
between the model predictive error and the objective in quantified uncertainty when costs for
misclassification errors or unbalanced datasets are asymmetric. We develop cost-sensitive
modifications of the neural networks in disease detection and propose metrics to measure the
quality of quantified uncertainty. Finally, we leverage an adaptive binning strategy to measure
uncertainty calibration error that directly corresponds to estimated uncertainty performance
and address problematic evaluation methods.
We evaluate the effectiveness of the tools on nuclei images segmentation, multi-class
Brain MRI image classification, multi-level cell type-specific protein expression prediction in
ImmunoHistoChemistry (IHC) images and cost-sensitive classification for Covid-19 detection
from X-Rays and CT image dataset. Our approach is thoroughly validated by measuring the
quality of uncertainty. It produces an equally good or better result and paves the way for the
future that addresses the practical problems at the intersection of deep learning and Bayesian
decision theory.
In conclusion, our study highlights the opportunities and challenges of the application of
estimated uncertainty in deep learning models of medical images, representing the confidence of the modelâs prediction, and the uncertainty quality metrics show a significant improvement
when using Deep Ensembles Bayesian Neural Networks with DropWeights
Simple, Efficient and Convenient Decentralized Multi-Task Learning for Neural Networks
Artificial intelligence relying on machine learning is increasingly used on small, personal, network-connected devices such as smartphones and vocal assistants, and these applications will likely evolve with the development of the Internet of Things. The learning process requires a lot of data, often real usersâ data, and computing power. Decentralized machine learning can help to protect usersâ privacy by keeping sensitive training data on usersâ devices, and has the potential to alleviate the cost born by service providers by off-loading some of the learning effort to user devices. Unfortunately, most approaches proposed so far for distributed learning with neural network are mono-task, and do not transfer easily to multi-tasks problems, for which users seek to solve related but distinct learning tasks and the few existing multi-task approaches have serious limitations. In this paper, we propose a novel learning method for neural networks that is decentralized, multitask, and keeps usersâ data local. Our approach works with different learning algorithms, on various types of neural networks. We formally analyze the convergence of our method, and we evaluateits efficiency in different situations on various kind of neural networks, with different learning algorithms, thus demonstrating its benefits in terms of learning quality and convergence
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