Any dataset with unequal distribution between its majority and minority classes can be considered to have class imbalance, and in real-world applications, the severity of class imbalance can vary from minor to severe (high or extreme). A dataset can be considered imbalanced if the classes, e.g., fraud and non-fraud cases, are not equally represented. The majority class makes up most of the dataset, whereas the minority class, with limited dataset representation, is often considered the class of interest. With real-world datasets, class imbalance should be expected. If the degree of class imbalance for the majority class is extreme, then a classifier may yield high overall prediction accuracy since the model is likely predicting most instances as belonging to the majority class. Such a model is not practically useful, since it is often the prediction performance of the class of interest (i.e., minority class) that is more important for the domain experts [1]. He and Garcia [2] suggest that a popular viewpoint held by academic researchers defines imbalanced data as data with a high-class imbalance between its two classes, stating that high-class imbalance is reflected when the majority-to-minority class ratio ranges from

Healthcare in the United States (U.S.) is important in the lives of many citizens, but unfortunately the high costs of health-related services leave many patients with limited medical care. In response, the U.S. government has established and funded programs, such as Medicare [1], that provide financial assistance for qualifying people to receive needed medical services [2]. There are a number of issues facing healthcare and

Healthcare in the United States is a critical aspect of most people's lives, particularly for the aging demographic. This rising elderly population continues to demand more cost-effective healthcare programs. Medicare is a vital program serving the needs of the elderly in the United States. The growing number of Medicare beneficiaries, along with the enormous volume of money in the healthcare industry, increases the appeal for, and risk of, fraud. In this paper, we focus on the detection of Medicare Part B provider fraud which involves fraudulent activities, such as patient abuse or neglect and billing for services not rendered, perpetrated by providers and other entities who have been excluded from participating in Federal healthcare programs. We discuss Part B data processing and describe a unique process for mapping fraud labels with known fraudulent providers. The labeled big dataset is highly imbalanced with a very limited number of fraud instances. In order to combat this class imbalance, we generate seven class distributions and assess the behavior and fraud detection performance of six different machine learning methods. Our results show that RF100 using a 90:10 class distribution is the best learner with a 0.87302 AUC. Moreover, learner behavior with the 50:50 balanced class distribution is similar to more imbalanced distributions which keep more of the original data. Based on the performance and significance testing results, we posit that retaining more of the majority class information leads to better Medicare Part B fraud detection performance over the balanced datasets across the majority of learners.

IntroductionThe exponential increase of raw data in recent years has been associated with technological advances in the fields of Data Mining (DM) and Machine Learning (ML) [1,2]. These advances have significantly improved the efficiency and effectiveness of Big Data applications in a diverse range of areas, such as knowledge discovery and information processing. Big Data is identified by various data-related properties, and for this reason, an exact definition of Big Data remains elusive. One definition, presented by Senthilkumar et al. [3], relates Big Data to six V's: Volume, Variety, Velocity, Veracity, Variability, and Value. Volume is associated with the reams of data produced by an organization. AbstractSevere class imbalance between majority and minority classes in Big Data can bias the predictive performance of Machine Learning algorithms toward the majority (negative) class. Where the minority (positive) class holds greater value than the majority (negative) class and the occurrence of false negatives incurs a greater penalty than false positives, the bias may lead to adverse consequences. Our paper incorporates two case studies, each utilizing three learners, six sampling approaches, two performance metrics, and five sampled distribution ratios, to uniquely investigate the effect of severe class imbalance on Big Data analytics. The learners (Gradient-Boosted Trees, Logistic Regression, Random Forest) were implemented within the Apache Spark framework. The first case study is based on a Medicare fraud detection dataset. The second case study, unlike the first, includes training data from one source (SlowlorisBig Dataset) and test data from a separate source (POST dataset). Results from the Medicare case study are not conclusive regarding the best sampling approach using Area Under the Receiver Operating Characteristic Curve and Geometric Mean performance metrics. However, it should be noted that the Random Undersampling approach performs adequately in the first case study. For the SlowlorisBig case study, Random Undersampling convincingly outperforms the other five sampling approaches (Random Oversampling, ADAptive SYNthetic) when measuring performance with Area Under the Receiver Operating Characteristic Curve and Geometric Mean metrics. Based on its classification performance in both case studies, Random Undersampling is the best choice as it results in models with a significantly smaller number of samples, thus reducing computational burden and training time. which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.

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