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2. Building Classifiers to Predict the Start of Glucose-Lowering Pharmacotherapy Using Belgian Health Expenditure Data

Author

Claesen, Marc, De Smet, Frank, Gillard, Pieter, Mathieu, Chantal, and De Moor, Bart

Subjects
Statistics - Machine Learning, Computer Science - Information Retrieval, I.5.4, J.3
Abstract

Early diagnosis is important for type 2 diabetes (T2D) to improve patient prognosis, prevent complications and reduce long-term treatment costs. We present a novel risk profiling approach based exclusively on health expenditure data that is available to Belgian mutual health insurers. We used expenditure data related to drug purchases and medical provisions to construct models that predict whether a patient will start glucose-lowering pharmacotherapy in the coming years, based on that patient's recent medical expenditure history. The design and implementation of the modeling strategy are discussed in detail and several learning methods are benchmarked for our application. Our best performing model obtains between 74.9% and 76.8% area under the ROC curve, which is comparable to state-of-the-art risk prediction approaches for T2D based on questionnaires. In contrast to other methods, our approach can be implemented on a population-wide scale at virtually no extra operational cost. Possibly, our approach can be further improved by additional information about some risk factors of T2D that is unavailable in health expenditure data., Comment: 23 pages, 5 figures, submitted to JMLR special issue on Learning from Electronic Health Data

Published
2015

3. Assessing binary classifiers using only positive and unlabeled data

Author

Claesen, Marc, Davis, Jesse, De Smet, Frank, and De Moor, Bart

Subjects
Statistics - Machine Learning, Computer Science - Information Retrieval, Computer Science - Learning, I.5.2
Abstract

Assessing the performance of a learned model is a crucial part of machine learning. However, in some domains only positive and unlabeled examples are available, which prohibits the use of most standard evaluation metrics. We propose an approach to estimate any metric based on contingency tables, including ROC and PR curves, using only positive and unlabeled data. Estimating these performance metrics is essentially reduced to estimating the fraction of (latent) positives in the unlabeled set, assuming known positives are a random sample of all positives. We provide theoretical bounds on the quality of our estimates, illustrate the importance of estimating the fraction of positives in the unlabeled set and demonstrate empirically that we are able to reliably estimate ROC and PR curves on real data., Comment: 14 pages, 8 figures

Published
2015

4. EnsembleSVM: A Library for Ensemble Learning Using Support Vector Machines

Author

Claesen, Marc, De Smet, Frank, Suykens, Johan, and De Moor, Bart

Subjects
Statistics - Machine Learning, Computer Science - Learning, G.3, I.2.6, I.5.1
Abstract

EnsembleSVM is a free software package containing efficient routines to perform ensemble learning with support vector machine (SVM) base models. It currently offers ensemble methods based on binary SVM models. Our implementation avoids duplicate storage and evaluation of support vectors which are shared between constituent models. Experimental results show that using ensemble approaches can drastically reduce training complexity while maintaining high predictive accuracy. The EnsembleSVM software package is freely available online at http://esat.kuleuven.be/stadius/ensemblesvm., Comment: 5 pages, 1 table

Published
2014

5. Fast Prediction with SVM Models Containing RBF Kernels

Author

Claesen, Marc, De Smet, Frank, Suykens, Johan A. K., and De Moor, Bart

Subjects
Statistics - Machine Learning, Computer Science - Learning, G.3, I.2.6, I.5.1
Abstract

We present an approximation scheme for support vector machine models that use an RBF kernel. A second-order Maclaurin series approximation is used for exponentials of inner products between support vectors and test instances. The approximation is applicable to all kernel methods featuring sums of kernel evaluations and makes no assumptions regarding data normalization. The prediction speed of approximated models no longer relates to the amount of support vectors but is quadratic in terms of the number of input dimensions. If the number of input dimensions is small compared to the amount of support vectors, the approximated model is significantly faster in prediction and has a smaller memory footprint. An optimized C++ implementation was made to assess the gain in prediction speed in a set of practical tests. We additionally provide a method to verify the approximation accuracy, prior to training models or during run-time, to ensure the loss in accuracy remains acceptable and within known bounds., Comment: 9 pages, 1 figure, 3 tables

Published
2014

6. A Robust Ensemble Approach to Learn From Positive and Unlabeled Data Using SVM Base Models

Author

Claesen, Marc, De Smet, Frank, Suykens, Johan A. K., and De Moor, Bart

Subjects
Statistics - Machine Learning, Computer Science - Learning, G.3, I.2.6, I.5.1
Abstract

We present a novel approach to learn binary classifiers when only positive and unlabeled instances are available (PU learning). This problem is routinely cast as a supervised task with label noise in the negative set. We use an ensemble of SVM models trained on bootstrap resamples of the training data for increased robustness against label noise. The approach can be considered in a bagging framework which provides an intuitive explanation for its mechanics in a semi-supervised setting. We compared our method to state-of-the-art approaches in simulations using multiple public benchmark data sets. The included benchmark comprises three settings with increasing label noise: (i) fully supervised, (ii) PU learning and (iii) PU learning with false positives. Our approach shows a marginal improvement over existing methods in the second setting and a significant improvement in the third., Comment: 34 pages, 6 figures, 6 tables. Accepted for publication in Neurocomputing: Special Issue on Advances in Learning with Label Noise

Published
2014
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25. Dynamics of HPV vaccination initiation in Flanders (Belgium) 2007-2009: a Cox regression model

Author

Hens Niel, Lefevere Eva, De Smet Frank, and Van Damme Pierre

Subjects
Public aspects of medicine, RA1-1270
Abstract

Abstract Background We investigated dynamic patterns and predictors of HPV vaccination initiation in Flanders (Belgium) by girls aged 12 to 18, between 2007 and 2009, the period immediately after the introduction of the HPV vaccines on the Belgian market. During this period the initiative for vaccination was taken by the girl, her family or the general practitioner/pediatrician/gynecologist. Methods We used a Cox regression model with time constant and time varying predictors to model hazard rates of HPV vaccination initiation. The sample existed of 117,151 female members of the National Alliance of Christian Mutualities, the largest sickness fund in Flanders. Results The study showed that the hazard of HPV vaccination initiation was higher (1) for older girls, (2) for girls with a more favorable socio-economic background, (3) under more generous reimbursement regimes (with this effect being more pronounced for girls with weak socioeconomic backgrounds), (4) for girls that were informed personally about the reimbursement rules. Conclusions When the initiative for HPV vaccination lies with the girls, their families or the physicians (no organized setting) the uptake of the vaccines is affected by both individual and organizational factors.

Published
2011
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26. Expression profiling to predict the clinical behaviour of ovarian cancer fails independent evaluation

Author

Amant Frederic, Engelen Kristof, Pochet Nathalie, Van Gorp Toon, De Smet Frank, Gevaert Olivier, De Moor Bart, Timmerman Dirk, and Vergote Ignace

Subjects
Neoplasms. Tumors. Oncology. Including cancer and carcinogens, RC254-282
Abstract

Abstract Background In a previously published pilot study we explored the performance of microarrays in predicting clinical behaviour of ovarian tumours. For this purpose we performed microarray analysis on 20 patients and estimated that we could predict advanced stage disease with 100% accuracy and the response to platin-based chemotherapy with 76.92% accuracy using leave-one-out cross validation techniques in combination with Least Squares Support Vector Machines (LS-SVMs). Methods In the current study we evaluate whether tumour characteristics in an independent set of 49 patients can be predicted using the pilot data set with principal component analysis or LS-SVMs. Results The results of the principal component analysis suggest that the gene expression data from stage I, platin-sensitive advanced stage and platin-resistant advanced stage tumours in the independent data set did not correspond to their respective classes in the pilot study. Additionally, LS-SVM models built using the data from the pilot study – although they only misclassified one of four stage I tumours and correctly classified all 45 advanced stage tumours – were not able to predict resistance to platin-based chemotherapy. Furthermore, models based on the pilot data and on previously published gene sets related to ovarian cancer outcomes, did not perform significantly better than our models. Conclusion We discuss possible reasons for failure of the model for predicting response to platin-based chemotherapy and conclude that existing results based on gene expression patterns of ovarian tumours need to be thoroughly scrutinized before these results can be accepted to reflect the true performance of microarray technology.

Published
2008
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27. Privacy in tijden van internet, sociale netwerken en big data

Author

Yolanda, Berbers, Debeuckelaere, Willem, De Hert, Paul, Desmedt, Yvo, De Smet, Frank, Hildebrandt, Mireille, Poels, Karolien, Pierson, Jos, Preneel, Bart, Vandewalle, Joos, Europees Criminologisch Recht, Metajuridica, Recht Wetenschap Technologie en Samenleving, Fundamentele rechten centrum, Studies van Media, Vernieuwing en Technologie, Communicatiewetenschappen, and Brussels Centrum voor Mededingingsbeleid

Subjects
Big Data, Internet, sociale netwerken, privacy, sociale media
Abstract

Dit is een Standpunt van de KVAB inzake privacy en gegevensbescherming in tijden van Big Data., The current use of the internet, social media and big data severely affects the privacy of ordinary users This positioning paper is primarily aimed at the private user young and old who did not have special education or training regarding ICT but still uses these services intensively and who, whether or not, rightly worries about the hazards to which his or her privacy is exposed This requires not only a better and deeper understanding of the technological possibilities and limitations, but also the commercial interests, and their relation to the constraints and threats of our personal privacy when using the many often valuable services. The speci c aspects of privacy as patients, or the privacy regulations for companies and institutions that track and process les with data from individuals, employees, students, or customers, is not dealt with but is referred to other reports This positioning paper has been conceived by a working group of members of KVAB and external experts covering the different aspectsof this interdisciplinary subject, that have met regularly over a period of one year. Since the ICT world is often overwhelmed with “jargon” words, the scope of which does not penetrate or because the newspapers sometimes describe very frightening lowly-backed situations, we rst discuss the main concepts both at the level of the machine learning, data extraction and the big data, as well as the privacy issues that arise, and nally the ways in which a better privacy can be acquired . In order to make this more concrete for the modal reader, we discuss important privacy hazards in a number of concrete situations, such as the digital life of a family, the big data police in passenger pro les, the internet of things, the context of smart cities, distributed information versus central collection, autonomous vehicles, and location information Although this digital revolution is not over yet, the modal user can already modify his behavior. There is extensive scienti c literature on this subject, but there are also many widely accessible texts available recently, including websites, to which the interested reader is referred to in the bibliography.

Published
2017

32. The health and economic burden of haemophilia in Belgium: a rare, expensive and challenging disease

Author

UCL - SSS/IRSS - Institut de recherche santé et société, UCL - (SLuc) Service d'hématologie, UCL - SSS/IREC/CARD - Pôle de recherche cardiovasculaire, Henrard, Séverine, Devleesschauwer, Brecht, Beutels, Philippe, Callens, Michael, De Smet, Frank, Hermans, Cedric, Speybroeck, Niko, UCL - SSS/IRSS - Institut de recherche santé et société, UCL - (SLuc) Service d'hématologie, UCL - SSS/IREC/CARD - Pôle de recherche cardiovasculaire, Henrard, Séverine, Devleesschauwer, Brecht, Beutels, Philippe, Callens, Michael, De Smet, Frank, Hermans, Cedric, and Speybroeck, Niko

Abstract

BACKGROUND: Haemophilia is a rare hereditary haemorrhagic disease that requires regular intravenous injections of clotting factor (CF) concentrates. This study sought to estimate the health and economic burden of haemophilia in Belgium. This is the first study of its type to be conducted, and reflects the Belgian authorities' growing interest for haemophilia as part of their priority planning for rare and chronic diseases. METHODS: A probabilistic model was developed in order to estimate the lifetime haemophilia burden for the 2011 birth-year Belgian cohort. The health burden was initially expressed in terms of disability-adjusted life years (DALYs), the number of healthy life years lost due to living with disability and dying prematurely. An incidence perspective was used in line with World Health Organization recommendations. The economic burden calculated from direct and indirect haemophilia-related costs was expressed in euros. Data were drawn from the literature if none were available from federal institutions or health insurance. Disability weights for DALY calculation were derived using generic quality-of-life tools such as SF-6D from the SF-36 (36-item Short-Form Health Survey; for adults) and KINDL (generic quality-of-life instrument; for children) compared to population norms. Analyses were stratified according to haemophilia type and severity. RESULTS: In Belgium, haemophilia resulted in 145 undiscounted and unweighted DALYs in total (95% credible interval [CrI] = 90-222), which represents an average of 11 DALYs per incident case with haemophilia (95% CrI = 8-15) during his life, varying according to haemophilia severity (17 DALYs for severe haemophilia, 12 DALYs for moderate, and 4 DALYs for mild). Mean total lifetime costs reached €7.8 million per people with haemophilia, 94.3% being direct costs and 5.7% indirect costs. Clotting factors accounted for 82.5% of direct costs. CONCLUSIONS: Haemophilia represents both an economic and health burden, especial

Published
2014

33. The disability adjusted life years (DALYs) and economic burden due to haemophilia in Belgium

Author

UCL - SSS/IRSS - Institut de recherche santé et société, UCL - (SLuc) Service d'hématologie, Henrard, Séverine, Devleesschauwer, Brecht, Beutels, Philippe, Callens, Michael, De Smet, Frank, Hermans, Cédric, Speybroeck, Niko, World Federation of Hemophilia 2014 World Congress, UCL - SSS/IRSS - Institut de recherche santé et société, UCL - (SLuc) Service d'hématologie, Henrard, Séverine, Devleesschauwer, Brecht, Beutels, Philippe, Callens, Michael, De Smet, Frank, Hermans, Cédric, Speybroeck, Niko, and World Federation of Hemophilia 2014 World Congress

Abstract

Introduction and Objectives: Haemophilia is a rare hereditary haemorrhagic disease that requires regular intravenous injections of clotting factor (CF) concentrates. This study sought to estimate the health and economic burden of haemophilia in Belgium. This is the first study of its type to be conducted, and reflects the European and Belgian authorities’ growing interest for haemophilia as part of their planning for rare diseases. Materials and Methods: A probabilistic model was developed in order to estimate the lifetime haemophilia burden for the 2011 birth-year Belgian cohort. The health burden was initially expressed in disability-adjusted life years (DALYs) lost, this being the number of lost healthy years due to both disability and premature mortality. An incidence perspective was used in line with World Health Organization recommendations. The economic burden calculated from direct and indirect haemophilia-related costs was expressed in euro. Data were drawn from the literature if none were available from federal institutions or health insurance. Disability weights for DALY calculation were derived using generic quality-of-life tools compared to population norms. Analyses were stratified according to haemophilia type and severity. Results: In Belgium, haemophilia resulted in 145 undiscounted and unweighted DALYs in total (95% credible interval [CrI]=90-222), which represents an average of 11 DALYs per incident case with haemophilia (95% CrI=8-15) during his life, varying according to haemophilia severity (17 DALYs for severe haemophilia, 12 DALYs for moderate, and 4 DALYs for mild). Mean total lifetime costs reached €7.8 million per people with haemophilia, 94.3% being direct costs and 5.7% indirect costs. CF accounted for 82.5% of direct costs. Conclusion: Haemophilia represents both an economic and health burden, especially regarding individual health on an individual patient level. Initiatives to counteract this burden should be clearly identified and giv

Published
2014

37. The health and economic burden of haemophilia in Belgium: a rare, expensive and challenging disease

Author

UCL - SSS/IRSS - Institut de recherche santé et société, UCL - (SLuc) Service d'hématologie, Henrard, Séverine, Devleesschauwer, Brecht, Beutels, Philippe, Callens, Michael, De Smet, Frank, Hermans, Cedric, Speybroeck, Niko, 21th Annual Meeting of the Belgian Society on Thrombosis and Haemostasis, UCL - SSS/IRSS - Institut de recherche santé et société, UCL - (SLuc) Service d'hématologie, Henrard, Séverine, Devleesschauwer, Brecht, Beutels, Philippe, Callens, Michael, De Smet, Frank, Hermans, Cedric, Speybroeck, Niko, and 21th Annual Meeting of the Belgian Society on Thrombosis and Haemostasis

Abstract

Background Haemophilia is a rare hereditary haemorrhagic disease that requires regular intravenous injections of clotting factor (CF) concentrates. This study sought to estimate the health and economic burden of haemophilia in Belgium. This is the first study of its type to be conducted, and reflects the Belgian authorities’ growing interest for haemophilia as part of their priority planning for rare and chronic diseases. Methods A probabilistic model was developed in order to estimate the lifetime haemophilia burden for the 2011 birth-year Belgian cohort. The health burden was initially expressed in disability-adjusted life years (DALYs) lost, this being the number of lost healthy years due to both disability and premature mortality. An incidence perspective was used in line with World Health Organization recommendations. The economic burden calculated from direct and indirect haemophilia-related costs was expressed in euro. Data was drawn from the literature if none was available from federal institutions or health insurance. Disability weights for DALY calculation were derived using generic quality-of-life tools such as SF-36 (36-item Short-Form Health Survey; for adults) and KINDL (generic quality-of-life instrument for children) compared to population norms. Analyses were stratified according to haemophilia type and severity. Results In Belgium, haemophilia resulted in 145 healthy years lost due to morbidity, invalidity or early death (or DALYs) in total (95% credible interval [CrI]=90-222), which represents an average of 11 DALYs per incident case with haemophilia (PWH) (95% CrI=8-15) during his life, varying according to haemophilia severity (17 DALYs for severe haemophilia, 12 DALYs for moderate, and 4 DALYs for mild). Mean total lifetime costs reached 7.8 million euro per PWH, 94.3% being direct costs and 5.7% indirect costs. Clotting factors accounted for 82.5% of direct costs. Conclusions Haemophilia represents both an economic and health burden, especial

Published
2013

39. Cancer During Pregnancy: An Analysis of 215 Patients Emphasizing the Obstetrical and the Neonatal Outcomes.

Author

UCL - MD/GYPE - Département de gynécologie, d'obstétrique et de pédiatrie, Van Calsteren, Kristel, Heyns, Liesbeth, De Smet, Frank, Van Eycken, Liesbet, Mhallem Gziri, Anissa, Van Gemert, Willemijn, Halaska, Michael, Vergote, Ignace, Ottevanger, Nelleke, Amant, Frédéric, UCL - MD/GYPE - Département de gynécologie, d'obstétrique et de pédiatrie, Van Calsteren, Kristel, Heyns, Liesbeth, De Smet, Frank, Van Eycken, Liesbet, Mhallem Gziri, Anissa, Van Gemert, Willemijn, Halaska, Michael, Vergote, Ignace, Ottevanger, Nelleke, and Amant, Frédéric

Abstract

PURPOSE: The aim of this study was to assess the management and the obstetrical and neonatal outcomes of pregnancies complicated by cancer. PATIENTS AND METHODS: In an international collaborative setting, patients with invasive cancer diagnosed during pregnancy between 1998 and 2008 were identified. Clinical data regarding the cancer diagnosis and treatment and the obstetric and neonatal outcomes were collected and analyzed. RESULTS: Of 215 patients, five (2.3%) had a pregnancy that ended in a spontaneous miscarriage and 30 (14.0%) pregnancies were interrupted. Treatment was initiated during pregnancy in 122 (56.7%) patients and postpartum in 58 (27.0%) patients. The most frequently encountered cancer types were breast cancer (46%), hematologic malignancies (18%), and dermatologic malignancies (10%). The mean gestational age at delivery was 36.3 +/- 2.9 weeks. Delivery was induced in 71.7% of pregnancies, and 54.2% of children were born preterm. In the group of patients prenatally exposed to cytotoxic treatment, the prevalence of preterm labor was increased (11.8%; P = .012). Furthermore, in this group a higher proportion of small-for-gestational-age children (birth weight below 10th percentile) was observed (24.2%; P = .001). Of all neonates, 51.2% were admitted to a neonatal intensive care unit, mainly (85.2%) because of prematurity. There was no increased incidence of congenital malformations. CONCLUSION: Pregnant cancer patients should be treated in a multidisciplinary setting with access to maternal and neonatal intensive care units. Prevention of iatrogenic prematurity appears to be an important part of the treatment strategy.

Published
2009

46. Revealing age-specific past and future unrelated costs of pneumococcal infections by flexible generalized estimating equations.

Author

Creemers, An, Aerts, Marc, Hens, Niel, Shkedy, Ziv, De Smet, Frank, and Beutels, Philippe

Subjects
LINEAR statistical models, STREPTOCOCCAL diseases, ESTIMATION theory, STREPTOCOCCUS pneumoniae, AGE groups
Abstract

We aimed to study the excess health-care expenditures for persons with a known positive isolate of Streptococcus pneumoniae. The data set was compiled by linking the database of the largest Belgian Sickness Fund with data obtained from laboratories reporting pneumococcal isolates. We analyzed the age-specific per-patient cumulative costs over time, using generalized estimating equations (GEEs). The mean structure was described by fractional polynomials. The quasi-likelihood under the independence model criterion was used to compare different correlation structures. We show for all age groups that the health-care costs incurred by diagnosed pneumococcal patients are significantly larger than those incurred by undiagnosed matched persons. This is not only the case at the time of diagnosis but also long before and after the time of diagnosis. These findings can be informative for the current debate on unrelated costs in health economic evaluation, and GEEs could be used to estimate these costs for other diseases. Finally, these results can be used to inform policy on the expected budget impact of preventing pneumococcal infections. [ABSTRACT FROM AUTHOR]

Published
2011
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