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Since Altman’s 1968 discriminant analysis model for corporate bankruptcy prediction, there have been numerous studies applying statistical and machine learning (ML) models in predicting bankruptcy under various contexts. ML models have been proven to be highly accurate in bankruptcy prediction up to three years before the event, more so than statistical models. A major limitation of ML models is that they suffer from an inability to handle highly imbalanced datasets, which has resulted in the development of a plethora of oversampling and undersampling methods for addressing class imbalances. However, current research on the impact of different sampling methods on the predictive performance of ML models is fragmented, inconsistent, and limited. This thesis investigated whether the choice of sampling method led to significant differences in the performance of five predictive algorithms: logistic regression, multiple discriminant analysis(MDA), random forests, Extreme Gradient Boosting (XGBoost), and support vector machines(SVM). Four oversampling methods (random oversampling (ROWR), synthetic minority oversampling technique (SMOTE), oversampling based on propensity scores (OBPS), and oversampling based on weighted nearest neighbour (WNN)) and three undersampling methods (random undersampling (RU), undersampling based on clustering from nearest neighbour (CFNN), and undersampling based on clustering from Gaussian mixture methods (GMM) were tested. The dataset was made up of non-listed Swedish restaurant businesses (1998 – 2021) obtained from the business registry of Sweden, having 10,696 companies with 335 bankrupt instances. Results, assessed through 10-fold cross-validated AUC scores, reveal those oversampling methods generally outperformed undersampling methods. SMOTE performed highest in four of five algorithms, while WNN performed highest with the random forest model. Results of Wilcoxon’s signed rank test showed that some differences between oversampling and undersampling were statistically significant, but differences within each group were not significant. Further, results showed that while the XGBoost had the highest AUC score of all predictive algorithms, it was also the most sensitive to different sampling methods, while MDA was the least sensitive. Overall, it was concluded that the choice of sampling method can significantly impact the performance of different algorithms, and thus users should consider both the algorithm’s sensitivity and the comparative performance of the sampling methods. The thesis’s results challenge some prior findings and suggests avenues for further exploration, highlighting the importance of selecting appropriate sampling methods when working with highly imbalanced datasets.

Deep learning models for scanned document image classification and form understand- ing have made significant progress in the last few years. High accuracy can be achieved by a model with the help of copious amounts of labelled training data for closed-world classification. However, very little work has been done in the domain of fine-grained and head-tailed(class imbalance with some classes having high numbers of data points and some having a low number of data points) open-world classification for documents. Our proposed method achieves a better classification results than the baseline of the head-tail-novel/open dataset. Our techniques include separating the head-tail classes and transferring the knowledge from head data to the tail data. This transfer of knowledge also improves the capability of recognizing a novel category by 15% as compared to the baseline.

The aim of this thesis is to focus on external imbalance and fiscal imbalance, which are recognized to be the cause of financial crisis in Europe, in Slovakia and Estonia. The first part of the thesis is dedicated to provide a theoretical background of external imbalance of current account deficit and deficit of balance of payment. As well to provide the definition of causes and consequences of creation of state budget, public debt and graphic interpretation of economic tools by using IS-LM-BP model. The aim of the practical part of my thesis is based on analysis of balance of, deficit of state budget and public debt of Slovakia and Estonia. I particularly focused on processes that vanish the imbalances by financing with and without debt, market equalization process and active economic policy. Furthermore, I designed a graphic evolution of Slovakia and Estonia in the period of time after the spread of financial crisis by using the IS-LM-BP model.

Homecare work is commonly described as a job involving high workload. Homecare in Sweden is affected by difficulties regarding recruiting and retaining employees. The aim of this study is to analyze the relationship between workload and the homecare employee's intention to quit their work. Workload is examined based on three dimensions: temporal, physical and relational workload. Result from frequency analysis shows that workload exists in all three dimensions. The physical dimension shows the highest percentage of workload of all three dimensions. Results from multiple logistic regressions shows that eight of nine examined variables increases the odds of homecare employee's intention to quit their work. The only examined variable that does not increase the odds is to feel inadequate regarding the care recipient’s needs. The results indicate, with the help of the effort-reward imbalance model, that there is an imbalance between homecare workers' efforts and rewards. Furthermore, the findings suggest that improvements regarding homecare employees' work situation are needed such as rewarding employees more for their efforts.

Motivation The prevalence of cardiovascular disease is on the increase in sub-Saharan Africa largely owing to lifestyle changes associated with urbanisation. Traditional diets are being replaced with diets high in saturated fat and sugar. In addition to the nutritional transition, urbanisation in developing African countries also contributes to a more sedentary lifestyle. Together these trends contribute to a higher prevalence of obesity and hypertension that are major risk factors for the development of cardiovascular disease. Adipose tissue is now widely recognised as an endocrine organ that secretes numerous inflammatory mediators as well as adipocytokines such as leptin. The primary role of leptin is to induce satiety after a meal and to suppress appetite. However, in recent years the role of leptin in the development of obesity-related cardiovascular disease has gained increasing attention and interest. Furthermore, leptin levels not only differ with regard to gender but also ethnicity. Africans have higher leptin levels than Caucasians due to higher subcutaneous fat in Africans. Furthermore, the prevalence of hypertension and stroke are also greater in the African population. Taken together, it is important to investigate mechanisms by which elevated leptin may contribute to the development of cardiovascular disease, especially in cardiovascular disease-prone Africans. Aim The general aim of this study is to increase our understanding of the role of leptin in cardiovascular disease development by investigating associations of leptin with markers of sympathetic activity, endothelial dysfunction, and cardiovascular reactivity and recovery in Africans and Caucasians. Methodology Data from the SABPA (Sympathetic activity and Ambulatory Blood Pressure in Africans) study was used and presented in the original research articles described in Chapter 2, 3 and 4. This study included 409 African and Caucasian schoolteachers working in the Potchefstroom district in the North West Province of South Africa. Groups were stratified by ethnicity, gender and ethnicity or obesity in order to demonstrate potential differences. We performed cardiovascular measurements and determined levels of leptin, renin, cortisol, plasminogen activator inhibitor-1 (PAI-1), von Willebrand factor (vWF) and urinary albumin-to-creatinine ratio (ACR). Independent t-tests were done to compare means between groups and Chi-square tests to compare proportions. Pearson’s correlations were determined to investigate associations as well as partial correlations after minimal adjustment for potential confounders. Multiple regression analyses were performed to investigate independent associations of leptin with cardiovascular and biochemical markers according to the specific focus of each research manuscript. Results and conclusions of the individual manuscripts  Leptin may contribute to obesity-related hypertension through its sympatho-activating effects. In the first research article (Chapter 2), we compared mean leptin levels and markers of autonomic activity between Africans and Caucasians. We also investigated associations between markers of autonomic activity and leptin. Africans had higher leptin, body mass index, blood pressure and heart rate compared to Caucasians. Furthermore, Africans also demonstrated reduced heart rate variability that is indicative of autonomic imbalance. Markers of autonomic activity that collectively reflected sympathetic overactivity associated with leptin in both Africans and Caucasians, independent of significant covariates and confounders including body mass index. These findings suggest that leptin may contribute to the development of hypertension by inducing autonomic dysfunction.  Leptin exerts direct vascular effects and may thereby contribute to increased cardiovascular disease risk in the obese. We therefore investigated associations between circulating markers of endothelial dysfunction (PAI-1, vWF and ACR) and leptin in lean and obese groups, irrespective of ethnicity (Chapter 3). As expected, leptin and plasminogen activator inhibitor-1 antigen levels were higher in the obese group. We found no differences for von Willebrand factor antigen and urinary albumin-to-creatinine ratio. In the obese group, all markers of endothelial dysfunction were positively associated with leptin in univariate analysis. However, after full adjustment in multiple regression analyses, only the association with plasminogen activator inhibitor-1 remained significant. Higher leptin levels in the obese may possibly induce endothelial dysfunction through mechanisms related to thrombotic vascular disease.  Greater cardiovascular reactivity to stress and prolonged recovery thereafter associates with increased cardiovascular disease risk. In the final research article (Chapter 4), we therefore investigated the relationship between cardiovascular reactivity and recovery to acute stress, induced by the cold pressor test, and leptin in Africans and Caucasians. Africans demonstrated greater cardiovascular reactivity compared to Caucasians. Associations of blood pressure, stroke volume, cardiac output, total peripheral resistance and arterial compliance reactivity with leptin were investigated during the stressor application and 1, 3 and 5 minutes post-stressor. There were no independent associations between cardiovascular reactivity and leptin during the stressor, and a few correlations at 1 and 3 minutes post-stressor. Associations were mostly evident at 5 minutes post-stressor and in Africans. We argue that higher leptin levels relate to impaired post-stress recovery and thereby could contribute to hypertension development in Africans. General conclusion Elevated leptin relates to sympathetic overactivity, vascular damage and delayed post-stress recovery, and thereby could contribute to increased cardiovascular disease risk. / PhD (Physiology), North-West University, Potchefstroom Campus, 2015

Motivation The prevalence of cardiovascular disease is on the increase in sub-Saharan Africa largely owing to lifestyle changes associated with urbanisation. Traditional diets are being replaced with diets high in saturated fat and sugar. In addition to the nutritional transition, urbanisation in developing African countries also contributes to a more sedentary lifestyle. Together these trends contribute to a higher prevalence of obesity and hypertension that are major risk factors for the development of cardiovascular disease. Adipose tissue is now widely recognised as an endocrine organ that secretes numerous inflammatory mediators as well as adipocytokines such as leptin. The primary role of leptin is to induce satiety after a meal and to suppress appetite. However, in recent years the role of leptin in the development of obesity-related cardiovascular disease has gained increasing attention and interest. Furthermore, leptin levels not only differ with regard to gender but also ethnicity. Africans have higher leptin levels than Caucasians due to higher subcutaneous fat in Africans. Furthermore, the prevalence of hypertension and stroke are also greater in the African population. Taken together, it is important to investigate mechanisms by which elevated leptin may contribute to the development of cardiovascular disease, especially in cardiovascular disease-prone Africans. Aim The general aim of this study is to increase our understanding of the role of leptin in cardiovascular disease development by investigating associations of leptin with markers of sympathetic activity, endothelial dysfunction, and cardiovascular reactivity and recovery in Africans and Caucasians. Methodology Data from the SABPA (Sympathetic activity and Ambulatory Blood Pressure in Africans) study was used and presented in the original research articles described in Chapter 2, 3 and 4. This study included 409 African and Caucasian schoolteachers working in the Potchefstroom district in the North West Province of South Africa. Groups were stratified by ethnicity, gender and ethnicity or obesity in order to demonstrate potential differences. We performed cardiovascular measurements and determined levels of leptin, renin, cortisol, plasminogen activator inhibitor-1 (PAI-1), von Willebrand factor (vWF) and urinary albumin-to-creatinine ratio (ACR). Independent t-tests were done to compare means between groups and Chi-square tests to compare proportions. Pearson’s correlations were determined to investigate associations as well as partial correlations after minimal adjustment for potential confounders. Multiple regression analyses were performed to investigate independent associations of leptin with cardiovascular and biochemical markers according to the specific focus of each research manuscript. Results and conclusions of the individual manuscripts  Leptin may contribute to obesity-related hypertension through its sympatho-activating effects. In the first research article (Chapter 2), we compared mean leptin levels and markers of autonomic activity between Africans and Caucasians. We also investigated associations between markers of autonomic activity and leptin. Africans had higher leptin, body mass index, blood pressure and heart rate compared to Caucasians. Furthermore, Africans also demonstrated reduced heart rate variability that is indicative of autonomic imbalance. Markers of autonomic activity that collectively reflected sympathetic overactivity associated with leptin in both Africans and Caucasians, independent of significant covariates and confounders including body mass index. These findings suggest that leptin may contribute to the development of hypertension by inducing autonomic dysfunction.  Leptin exerts direct vascular effects and may thereby contribute to increased cardiovascular disease risk in the obese. We therefore investigated associations between circulating markers of endothelial dysfunction (PAI-1, vWF and ACR) and leptin in lean and obese groups, irrespective of ethnicity (Chapter 3). As expected, leptin and plasminogen activator inhibitor-1 antigen levels were higher in the obese group. We found no differences for von Willebrand factor antigen and urinary albumin-to-creatinine ratio. In the obese group, all markers of endothelial dysfunction were positively associated with leptin in univariate analysis. However, after full adjustment in multiple regression analyses, only the association with plasminogen activator inhibitor-1 remained significant. Higher leptin levels in the obese may possibly induce endothelial dysfunction through mechanisms related to thrombotic vascular disease.  Greater cardiovascular reactivity to stress and prolonged recovery thereafter associates with increased cardiovascular disease risk. In the final research article (Chapter 4), we therefore investigated the relationship between cardiovascular reactivity and recovery to acute stress, induced by the cold pressor test, and leptin in Africans and Caucasians. Africans demonstrated greater cardiovascular reactivity compared to Caucasians. Associations of blood pressure, stroke volume, cardiac output, total peripheral resistance and arterial compliance reactivity with leptin were investigated during the stressor application and 1, 3 and 5 minutes post-stressor. There were no independent associations between cardiovascular reactivity and leptin during the stressor, and a few correlations at 1 and 3 minutes post-stressor. Associations were mostly evident at 5 minutes post-stressor and in Africans. We argue that higher leptin levels relate to impaired post-stress recovery and thereby could contribute to hypertension development in Africans. General conclusion Elevated leptin relates to sympathetic overactivity, vascular damage and delayed post-stress recovery, and thereby could contribute to increased cardiovascular disease risk. / PhD (Physiology), North-West University, Potchefstroom Campus, 2015

International Telemetering Conference Proceedings / October 23-26, 2000 / Town & Country Hotel and Conference Center, San Diego, California / When designing transmitters for quadrature modulation schemes, the designer always tries to achieve good balance and symmetry of the in-phase (I) and quadrature (Q) branches of the modulator in terms of amplitude, phase, and offsets. Perfect balance between modulators is ideal but rarely if ever achieved. The Advance Range Telemetry (ARTM) program has placed indirect specifications on the remnant carrier and sideband levels which are controlled by modulator imbalance. These specifications will govern the ARTM programs first generation of Feher’s patented quadrature phase shift keying, version B (FQPSK-B) [9] airborne telemetry transmitters. The ARTM Program has also adopted test procedures for quantifying these modulation imbalances. This paper looks at the effects of modulator imbalances on spectral occupancy and bit error probability of the airborne telemetry link. It also outlines how these imbalances influence the levels in one of the ARTM specifications. Recommendations are presented based on the measured data for higher bit rate telemetry systems.