19,129 research outputs found
Request-and-Reverify: Hierarchical Hypothesis Testing for Concept Drift Detection with Expensive Labels
One important assumption underlying common classification models is the
stationarity of the data. However, in real-world streaming applications, the
data concept indicated by the joint distribution of feature and label is not
stationary but drifting over time. Concept drift detection aims to detect such
drifts and adapt the model so as to mitigate any deterioration in the model's
predictive performance. Unfortunately, most existing concept drift detection
methods rely on a strong and over-optimistic condition that the true labels are
available immediately for all already classified instances. In this paper, a
novel Hierarchical Hypothesis Testing framework with Request-and-Reverify
strategy is developed to detect concept drifts by requesting labels only when
necessary. Two methods, namely Hierarchical Hypothesis Testing with
Classification Uncertainty (HHT-CU) and Hierarchical Hypothesis Testing with
Attribute-wise "Goodness-of-fit" (HHT-AG), are proposed respectively under the
novel framework. In experiments with benchmark datasets, our methods
demonstrate overwhelming advantages over state-of-the-art unsupervised drift
detectors. More importantly, our methods even outperform DDM (the widely used
supervised drift detector) when we use significantly fewer labels.Comment: Published as a conference paper at IJCAI 201
Adaptive Online Sequential ELM for Concept Drift Tackling
A machine learning method needs to adapt to over time changes in the
environment. Such changes are known as concept drift. In this paper, we propose
concept drift tackling method as an enhancement of Online Sequential Extreme
Learning Machine (OS-ELM) and Constructive Enhancement OS-ELM (CEOS-ELM) by
adding adaptive capability for classification and regression problem. The
scheme is named as adaptive OS-ELM (AOS-ELM). It is a single classifier scheme
that works well to handle real drift, virtual drift, and hybrid drift. The
AOS-ELM also works well for sudden drift and recurrent context change type. The
scheme is a simple unified method implemented in simple lines of code. We
evaluated AOS-ELM on regression and classification problem by using concept
drift public data set (SEA and STAGGER) and other public data sets such as
MNIST, USPS, and IDS. Experiments show that our method gives higher kappa value
compared to the multiclassifier ELM ensemble. Even though AOS-ELM in practice
does not need hidden nodes increase, we address some issues related to the
increasing of the hidden nodes such as error condition and rank values. We
propose taking the rank of the pseudoinverse matrix as an indicator parameter
to detect underfitting condition.Comment: Hindawi Publishing. Computational Intelligence and Neuroscience
Volume 2016 (2016), Article ID 8091267, 17 pages Received 29 January 2016,
Accepted 17 May 2016. Special Issue on "Advances in Neural Networks and
Hybrid-Metaheuristics: Theory, Algorithms, and Novel Engineering
Applications". Academic Editor: Stefan Hauf
Email classification via intention-based segmentation
Email is the most popular way of personal and official communication among people and organizations. Due to untrusted virtual environment, email systems may face frequent attacks like malware, spamming, social engineering, etc. Spamming is the most common malicious activity, where unsolicited emails are sent in bulk, and these spam emails can be the source of malware, waste resources, hence degrade the productivity. In spam filter development, the most important challenge is to find the correlation between the nature of spam and the interest of the users because the interests of users are dynamic. This paper proposes a novel dynamic spam filter model that considers the changes in the interests of users with time while handling the spam activities. It uses intention-based segmentation to compare different segments of text documents instead of comparing them as a whole. The proposed spam filter is a multi-tier approach where initially, the email content is divided into segments with the help of part of speech (POS) tagging based on voices and tenses. Further, the segments are clustered using hierarchical clustering and compared using the vector space model. In the third stage, concept drift is detected in the clusters to identify the change in the interest of the user. Later, the classification of ham emails into various categories is done in the last stage. For experiments Enron dataset is used and the obtained results are promising
Learning Discrete-Time Markov Chains Under Concept Drift
Learning under concept drift is a novel and promising research area aiming at designing learning algorithms able to deal with nonstationary data-generating processes. In this research field, most of the literature focuses on learning nonstationary probabilistic frameworks, while some extensions about learning graphs and signals under concept drift exist. For the first time in the literature, this paper addresses the problem of learning discrete-time Markov chains (DTMCs) under concept drift. More specifically, following a hybrid active/passive approach, this paper introduces both a family of change-detection mechanisms (CDMs), differing in the required assumptions and performance, for detecting changes in DTMCs and an adaptive learning algorithm able to deal with DTMCs under concept drift. The effectiveness of both the proposed CDMs and the adaptive learning algorithm has been extensively tested on synthetically generated experiments and real data sets
Significance of log-periodic precursors to financial crashes
We clarify the status of log-periodicity associated with speculative bubbles
preceding financial crashes. In particular, we address Feigenbaum's [2001]
criticism and show how it can be rebuked. Feigenbaum's main result is as
follows: ``the hypothesis that the log-periodic component is present in the
data cannot be rejected at the 95% confidence level when using all the data
prior to the 1987 crash; however, it can be rejected by removing the last year
of data.'' (e.g., by removing 15% of the data closest to the critical point).
We stress that it is naive to analyze a critical point phenomenon, i.e., a
power law divergence, reliably by removing the most important part of the data
closest to the critical point. We also present the history of log-periodicity
in the present context explaining its essential features and why it may be
important. We offer an extension of the rational expectation bubble model for
general and arbitrary risk-aversion within the general stochastic discount
factor theory. We suggest guidelines for using log-periodicity and explain how
to develop and interpret statistical tests of log-periodicity. We discuss the
issue of prediction based on our results and the evidence of outliers in the
distribution of drawdowns. New statistical tests demonstrate that the 1% to 10%
quantile of the largest events of the population of drawdowns of the Nasdaq
composite index and of the Dow Jones Industrial Average index belong to a
distribution significantly different from the rest of the population. This
suggests that very large drawdowns result from an amplification mechanism that
may make them more predictable than smaller market moves.Comment: Latex document of 38 pages including 16 eps figures and 3 tables, in
press in Quantitative Financ
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