• The Korean Journal of Applied Statistics
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• v.37 no.4
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• pp.395-410
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• 2024

Text data is usually made up of a wide variety of unique words. Even in standard text data, it is common to find tens of thousands of different words. In text data analysis, usually, each unique word is treated as a variable. Thus, text data can be regarded as a dataset with a large number of variables. On the other hand, in text data classification, we often encounter class label imbalance problems. In the cases of substantial imbalances, the performance of conventional classification models can be severely degraded. To improve the classification performance of support vector machines (SVM) for imbalanced data, algorithms such as the Synthetic Minority Over-sampling Technique (SMOTE) can be used. The SMOTE algorithm synthetically generates new observations for the minority class based on the k-Nearest Neighbors (kNN) algorithm. However, in datasets with a large number of variables, such as text data, errors may accumulate. This can potentially impact the performance of the kNN algorithm. In this study, we propose a method for enhancing prediction performance for the minority class of imbalanced text data. Our approach involves employing variable selection to generate new synthetic observations in a reduced space, thereby improving the overall classification performance of SVM.

• KIPS Transactions on Software and Data Engineering
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• v.12 no.7
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• pp.295-302
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• 2023

Software requirements written in natural language may have different meanings from the stakeholders' viewpoint. When designing an architecture based on quality attributes, it is necessary to accurately classify quality attribute requirements because the efficient design is possible only when appropriate architectural tactics for each quality attribute are selected. As a result, although many natural language processing models have been studied for the classification of requirements, which is a high-cost task, few topics improve classification performance with the imbalanced quality attribute datasets. In this study, we first show that the classification model can automatically classify the Korean requirement dataset through experiments. Based on these results, we explain that data augmentation through EDA(Easy Data Augmentation) techniques and undersampling strategies can improve the imbalance of quality attribute datasets, and show that they are effective in classifying requirements. The results improved by 5.24%p on F1-score, indicating that handling imbalanced data helps classify Korean requirements of classification models. Furthermore, detailed experiments of EDA illustrate operations that help improve classification performance.

• Information Systems Review
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• v.24 no.4
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• pp.23-40
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• 2022

Although Support Vector Machine(SVM) has been used in various fields such as bankruptcy prediction model, the hyperplane learned by SVM in class imbalance problem can be severely skewed toward minority class and has a negative impact on performance because the area of majority class is expanded while the area of minority class is invaded. This study proposed optimized uneven margin SVM(OPT-UMSVM) combining threshold moving or post scaling method with UMSVM to cope with the limitation of the traditional even margin SVM(EMSVM) in class imbalance problem. OPT-UMSVM readjusted the skewed hyperplane to the majority class and had better generation ability than EMSVM improving the sensitivity of minority class and calculating the optimized performance. To validate OPT-UMSVM, 10-fold cross validations were performed on five sub-datasets with different imbalance ratio values. Empirical results showed two main findings. First, UMSVM had a weak effect on improving the performance of EMSVM in balanced datasets, but it greatly outperformed EMSVM in severely imbalanced datasets. Second, compared to EMSVM and conventional UMSVM, OPT-UMSVM had better performance in both balanced and imbalanced datasets and showed a significant difference performance especially in severely imbalanced datasets.

• Annual Conference on Human and Language Technology
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• 2021.10a
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• pp.221-226
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• 2021

우리는 범주 불균형 분류 문제를 해결하기 위해 학습 과정 중 범주 크기 기반 배치 샘플링 방법 전환을 위한 스케줄링 방법을 제안한다. 범주별 샘플링 확률로 범주 크기의 역수(LWRS-Reciporcal)와 범주 비율의 반수(LWRS-Ratio)를 적용하여 각각 실험을 진행하였고, LWRS-Reciporcal 방법이 F1 성능 개선에 더 효과적인 것을 확인하였다. 더하여 고정된 샘플링 확률값으로 인해 발생할 수 있는 또 다른 편향 문제를 완화하기 위해 학습 과정 중 샘플링 방법을 전환하는 스케줄링 방법을 설계하였다. 결과적으로 검증 성능의 갱신 유무로 샘플링 방법을 전환하였을 때 naver shopping 데이터셋과 KLUE-TC에 대하여 f1 score와 accuracy의 성능 합이 베이스라인보다 각각 0.7%, 0.8% 향상된 가장 이상적인 성능을 보임을 확인하였다.

• Annual Conference on Human and Language Technology
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• 2021.10a
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• pp.251-256
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• 2021

개체명 인식은 정보 추출의 하위 작업으로, 문서에서 개체명에 해당하는 단어를 찾아 알맞은 개체명을 분류하는 자연어처리 기술이다. 질의 응답, 관계 추출 등과 같은 자연어처리 작업에 대한 관심이 높아짐에 따라 세부 분류 개체명 인식에 대한 수요가 증가했다. 그러나 기존 개체명 인식 성능에 비해 세부 분류 개체명 인식의 성능이 낮다. 이러한 성능 차이의 원인은 세부 분류 개체명 데이터가 불균형하기 때문이다. 본 논문에서는 이러한 데이터 불균형 문제를 해결하기 위해 대분류 개체명 정보를 활용하여 세부 분류 개체명 인식을 수행하는 방법과 대분류 개체명 인식의 오류 전파를 완화하기 위한 2단계 학습 방법을 제안한다. 또한 레이블 주의집중 네트워크 기반의 구조에서 레이블의 공통 요소를 공유하여 세부 분류 개체명 인식에 효과적인 레이블 임베딩 구성 방법을 제안한다.

• Journal of Intelligence and Information Systems
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• v.28 no.4
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• pp.179-190
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• 2022

Data imbalance refers to a phenomenon in which the number of data in one category is too large or too small compared to another category. Due to this, it has been raised as a major factor that deteriorates performance in machine learning that utilizes classification algorithms. In order to solve the data imbalance problem, various ovrsampling methods for amplifying prime number distribution data have been proposed. Among them, SMOTE is the most representative method. In order to maximize the amplification effect of minority distribution data, various methods have emerged that remove noise included in data (SMOTE-IPF) or enhance only border lines (Borderline SMOTE). This paper proposes a method to ultimately improve classification performance by improving the processing method for anomaly data in the traditional SMOTE method that amplifies minority classification data. The proposed method consistently presented relatively high classification performance compared to the existing methods through experiments.

• The Korean Journal of Applied Statistics
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• v.27 no.3
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• pp.357-371
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• 2014

There are many studies related to imbalanced data in which the class distribution is highly skewed. To address the problem of imbalanced data, previous studies deal with resampling techniques which correct the skewness of the class distribution in each sampled subset by using under-sampling, over-sampling or hybrid-sampling such as SMOTE. Ensemble methods have also alleviated the problem of class imbalanced data. In this paper, we compare around a dozen algorithms that combine the ensemble methods and resampling techniques based on simulated data sets generated by the Backbone model, which can handle the imbalance rate. The results on various real imbalanced data sets are also presented to compare the effectiveness of algorithms. As a result, we highly recommend the resampling technique combining ensemble methods for imbalanced data in which the proportion of the minority class is less than 10%. We also find that each ensemble method has a well-matched sampling technique. The algorithms which combine bagging or random forest ensembles with random undersampling tend to perform well; however, the boosting ensemble appears to perform better with over-sampling. All ensemble methods combined with SMOTE outperform in most situations.

• The Korean Journal of Applied Statistics
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• v.34 no.4
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• pp.599-609
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• 2021

Data with a large difference in the number of objects between clusters are called unbalanced data. In discriminant analysis of unbalanced data, it is more important to classify objects in minority categories than to classify objects in majority categories well. However, objects in minority categories are often misclassified into majority categories. In this study, we propose a method that combined hierarchical DBSCAN (HDBSCAN) and SMOTE to solve this problem. Using HDBSCAN, it removes noise in minority categories and majority categories. Then it applies SMOTE to create new data. Area under the roc curve (AUC) and F1 scores were used to compare performance with existing methods. As a result, in most cases, the method combining HDBSCAN and synthetic minority oversampling technique (SMOTE) showed a high performance index, and it was found to be an excellent method for classifying unbalanced data.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.24 no.1
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• pp.49-54
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• 2024

Data imbalance is a common issue encountered in classification problems, stemming from a significant disparity in the number of samples between classes within the dataset. Such data imbalance typically leads to problems in classification models, including overfitting, underfitting, and misinterpretation of performance metrics. Methods to address this issue include resampling, augmentation, regularization techniques, and adjustment of loss functions. In this paper, we focus on loss function adjustment, particularly comparing the performance of various configurations of loss functions (Cross Entropy, Balanced Cross Entropy, two settings of Focal Loss: 𝛼 = 1 and 𝛼 = Balanced, Asymmetric Loss) on Multi-Class black-box video data with imbalance issues. The comparison is conducted using the I3D, and R3D_18 models.

• Proceedings of the Korean Operations and Management Science Society Conference
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• 2006.05a
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• pp.291-298
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• 2006

패턴인식 문제에서 한 범주에 속한 데이터의 수가 다른 범주에 속한 데이터의 수보다 극히 많거나 적으면 데이터 불균형이 발생했다고 한다. Support Vector Machine(SVM)은 다른 기계 학습 알고리즘들과 마찬가지로 학습에 사용되는 데이터의 범주간 비율이 거의 비슷하다는 가정 하에서 학습을 하고 예측 결과를 도출하게 된다. 그러나 실제 문제에서는 데이터의 불균형이 발생하는 경우가 매우 빈번하며, 이러한 경우에는 모델의 성능이 매우 저하되는 문제점이 발생한다. 본 논문에서는 실제로 데이터 불균형이 SVM의 분류 결과에 어떠한 영향을 미치는지를 2차원 인공 데이터를 통하여 알아본다. 그리고 이러한 데이터 불균형을 해소하기 위하여 Under-Sampling 기반 앙상블 SVM을 제안하였다. 제안된 방법을 두 가지 인공 데이터에 적용하여 본 결과, 제안된 방법은 데이터 불균형을 해소하기 위해 사용되는 기존의 방법들에 비하여 소수 범주에 속하는 데이터의 수가 매우 적고 데이터의 불균형이 매우 심한 경우에도 높은 성능과 안정성을 갖는 효과적인 방법이라는 것이 입증되었다.