Abstract
In this customs fraud detection application, we analyse a unique data set of 9,624,124 records resulting from a collaboration with the Belgian customs administration. They are faced with increasing levels of international trade, which pressurizes regulatory control. Governments therefore rely on data mining to focus their limited resources on the most likely fraud cases. The literature on data mining for customs fraud detection lacks in two main directions that are simultaneously addressed in this paper: (1) behavioural and high-cardinality data types are neglected due to a lack of methodology to include them. We demonstrate that such fine-grained features (e.g. the specific entities such as consignee, consignor and declarant and the commodities involved in a declaration) are very predictive. (2) Studies in the tax domain most often use standard learning algorithms on their fraud detection applications. However, customs data are highly imbalanced and this poses challenges for many inducers. We present a new EasyEnsemble method that integrates a support vector machine base learner in a confidence-rated boosting algorithm. This results in a fast and scalable learner that is able to drastically improve predictive performance over the base application of a support vector machine. The results of our proposed framework reveals high AUC and lift values that translate into an immediate impact on the customs fraud detection domain through an improved retrieval of tax losses and an enhanced deterrence.
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Notes
Legitimacy should be interpreted broadly and is not limited to verifying whether the imposed duties are paid and transport documents are filled in correctly. It also means protecting the environment and society against imported harmful/dangerous goods (e.g. counterfeit goods of low quality).
Additionally, national taxes such as value-added tax (VAT) and excises related to international trade transactions can be collected by customs authorities.
The taxable amount is the customs value or the amount on which the tax is levied.
We refer to https://financien.belgium.be/nl/Statistieken_en_analysen/jaarverslag/cijfers/budget-ontvangsten/ontvangsten-aa-douane-en-accijnzen-1 for additional figures (also including VAT and excises).
Trade facilitation means a rapid clearance of customs goods to have a minimal impact on economic commerce.
Each member country can stipulate a number of additional national regulations.
There are two types of inspections: (1) physical cargo checks when the goods enter the territory (e.g. inspecting containers). (2) Post-clearance audits which entail checking the books and verifying trade documents (e.g. invoices, SAD declarations) for irregularities. Regarding the former, Belgian customs impose a 6 second rule for the automated processing of an article involved in a SAD declaration (online environment). The post-clearance audit checks can be conducted up to 4 years after the date of declaration.
There exists a third category of techniques, the semi-supervised approaches, that learn a discriminative boundary around the instances of a single class [5]. However, they do not seem to be applied in the area of customs fraud detection.
Methods at algorithmic level are also called cost-sensitive learning techniques.
TARIC extends the Combined Nomenclature (CN) and contains tariffs for each commodity according to its country of origin. The CN is a tool for the harmonized classification of goods within the EU and is a further development (with special EU-specific subdivisions) of the WCO’s Harmonized System Nomenclature (HSN) [16].
In this study, in accordance with Moeyersoms and Martens [36], an attribute is of high-cardinality in case it has more than 100 different categories.
This means that imported goods are released for free circulation and their associated customs duties are levied in one member state (i.e. Belgium), yet payment of VAT (and where applicable excise duties) is suspended because the import is directly followed by an intra-community supply of the goods to another member state (i.e. France). VAT (and excises) are due in the member state of final destination (i.e. France).
A forwarding agent (or freight forwarder) [51] is an entity that organizes the delivery of goods, without doing the actual transportation. He is responsible for choosing the carriers that deliver the goods in the most effective way in terms of transportation time and costs. Furthermore, he prepares the necessary documents (customs and insurance) and transport certificates. The forwarding agent acts as an intermediary in the logistics chain.
The representative and intra-community acquirer occur far less frequently. Also note that the identity of the consignor is unknown in an import declaration.
Each row therefore contains four ones. This time we consider the entities simultaneously which allows interaction effects to be revealed. In the case of high-cardinality variables, each attribute is treated separately. The main difference lies in the modelling.
The margin denotes the separation between the two classes (i.e. how far are the instances from both classes separated from the learned hyperplane?). Maximizing the margin coincides with minimizing the model complexity \(w^Tw/2\).
Choosing a too large value for regularization parameter C results in a learner that is too sensitive on the training data (overfitting) and fails to generalize for unseen data. On the other hand, a too small value for C means that large errors can occur for the training data and a too simple model is obtained (underfitting) that is unable to distinguish between both classes.
The LR component transforms the real-valued SVM scores \(w^T\varphi (x) + b\) to the range \([-1,+1]\) (as required for a confidence-rated boosting algorithm).
In Sect. 5.1.2, we will detail which part of the training data is effectively used for calculating the SR values.
The AUC corresponds to the probability that a positive instance (fraud) is ranked higher than a negative instance (compliant). The ranking is obtained by sorting the instances according to the output scores produced by the classifier.
Within each fold, the feature selection based on t statistic is computed on the training data. The set of ‘optimal’ features can therefore differ in each fold.
We make use of the standard MATLAB function fitctree, see https://nl.mathworks.com/help/stats/fitctree.html, which fits a classification decision tree making binary splits. Default parameter settings are adopted. The split criterion is a hyperparameter that can take on Gini’s diversity index or maximum deviance reduction (cross entropy). The MinLeafSize (minimum number of leaf node observations) is another hyperparameter that controls for overfitting. The following values were imposed: MinLeafSize\(= 2^z\), with \(z = [1;1.5;2;2.5;\ldots ;5.5]\).
The standard MATLAB function patternnet, see https://nl.mathworks.com/help/deeplearning/ref/patternnet.html, is used to construct a classification neural network with one hidden layer (sigmoid transfer function). Default parameter settings are adopted for the optimization algorithm (scaled conjugate gradient) and performance function (cross-entropy). The number of hidden neurons is a hyperparameter taking on values \([5; 10; 15; 20;\ldots ; 100]\). We trained the neural network, with a given number of hidden neurons, for 10 times on the training data and selected the one with the best validation set performance (a neural network converges to a local optimum).
Based on counting the wins/losses/draws in comparing several methods. For example, in comparing the F with the S version, a pair (F,S) is formed with the same data set (2 types), the same type of pre-processing (3 types) and the same final model (4 types). This leads to checking a total of 24 pairs.
In the case of OperID data, this is always the case. These are precisely the attributes with the highest cardinalities for which we expect stability issues to occur.
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Acknowledgements
The authors would like to thank the Belgian Federal Public Service Finance division Customs and Excise for the provision of the data sets and their involvement throughout the project. The models described in this paper are not necessarily the ones used by the Belgian customs administration. Funding was provided by University of Antwerp (Grant No. DOCPRO4/Antigoon PS-IDnr. 29648).
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Appendices
Appendix 1: Single administrative document form
A blank SAD declaration form [13] is provided in Fig. 6. In Belgium, customs declarations are filed electronically by means of the PaperLess Douane en Accijnzen (PLDA) application.
Appendix 2: AdaBoost
Algorithm 1 presents the underlying AB boosting process for the EE technique that we have presented in Sect. 4.2.3.
Appendix 3: Data ensembles
Table 7 presents the results shown in Fig. 5 in a tabular format.
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Vanhoeyveld, J., Martens, D. & Peeters, B. Customs fraud detection. Pattern Anal Applic 23, 1457–1477 (2020). https://doi.org/10.1007/s10044-019-00852-w
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DOI: https://doi.org/10.1007/s10044-019-00852-w