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Radiograph examinations play a critical role in various applications such as the detection of bone pathologies and lung cancer, despite the challenge of false negatives. The integration of Artificial Intelligence (AI) holds promise in enhancing image quality and assisting radiologists in their diagnostic processes. However, the scarcity of annotated high-quality data poses a significant hurdle in training AI models effectively. In this thesis, we propose a method for training deep learning models using synthetic data to achieve segmentation of X-ray images. Realistic, simulated, images were generated, enabling segmentation of anatomical structures, including the spine, ribs, scapula, clavicle, and lungs, on a test set comprised of other simulated images. The foremost emphasize was placed on the segmentation of the spine, where we obtained a Dice score of 0.87. Significant advancements have also been made in the application of the model to real clinical images, demonstrating successful segmentation in certain instances. Further generalization of the model opens up numerous avenues for future exploration of deep learning in radiography. / Röntgenundersökningar har en avgörande roll inom flera områden, såsom detektering av bensjukdomar och lungcancer, trots en stor andel falska negativa resultat. Artificiell intelligens (AI) är ett lovande verktyg för att förbättra bildkvaliteten och underlätta radiologers arbete att diagnostisera patienter. Det är dock en brist på högkvalitativ, annoterad, data, vilket är ett signifikant hinder för effektiv träning av AI-modeller.  I detta arbete presenteras en metod för att träna djupinlärningsmodeller med hjälp av syntetisk data för att segmentera anatomier på röntgenbilder. Realistiska, simulerade, bilder genererades och möjliggjorde segmentering av ryggrad, revben, skulderblad, nyckelben och lungor på ett testset bestående av andra simulerade bilder. Störst vikt lades på segmentering av ryggrad, där ett Dice-resultat på 0.87 uppnåddes. Betydande framsteg har också gjorts i tillämpningen av modellen till verkliga kliniska bilder och lyckade segmenteringar åstadkoms i vissa exempel.  Ytterligare generalisering av modellen skulle öppna upp många möjligheter att undersöka användning av djupinlärning för röntgenbilder.

Generative models for creating realistic synthetic graphs constitute a research area that is increasing in popularity, especially as the use of graph data is becoming increasingly common. Generating realistic synthetic graphs enables sharing of the information embedded in graphs without directly sharing the original graphs themselves. This can in turn contribute to an increase of knowledge within several domains where access to data is normally restricted, including the financial system and social networks. In this study, it is examined how existing generative models can be extended to be compatible with directed and weighted graphs, without limiting the models to generating graphs of a specific domain. Several models are evaluated, and all use low-rank approximations to learn structural properties of directed graphs. Additionally, it is evaluated how node embeddings can be used with a regression model to add realistic edge weights to directed graphs. The results show that the evaluated methods are capable of reproducing global statistics from the original directed graphs to a promising degree, without having more than 52% overlap in terms of edges. The results also indicate that realistic directed and weighted graphs can be generated from directed graphs by predicting edge weights using pairs of node embeddings. However, the results vary depending on which node embedding technique is used.

Modern retailers have been collecting more and more data over the past decades. The increased sizes of collected data have led to higher demand for data analytics expertise tools, which the Umeå-founded company Infobaleen provides. A recurring challenge when developing such tools is the data itself. Difficulties in finding relevant open data sets have led to a rise in the popularity of using synthetic data. By using artificially generated data, developers gain more control over the input when testing and presenting their work. However, most methods that exist today either depend on real-world data as input or produce results that look synthetic and are difficult to extend. In this thesis, I introduce a method specifically designed to generate synthetic transactional data stochastically. I first examined real-world data provided by Infobaleen to determine suitable statistical distributions to use in my algorithm empirically. I then modelled individual decision-making using points in an embedding space, where the distance between the points serves as a basis for individually unique probability weights. This solution creates data distributed similarly to real-world data and enables retroactive data enrichment using the same embeddings. The result is a data set that looks genuine to the human eye but is entirely synthetic. Infobaleen already generates data with this model when presenting its product to new potential customers or partners.

Modern machine and deep learning methods require large datasets to achieve reliable and robust results. This requirement is often difficult to meet in the medical field, due to data sharing limitations imposed by privacy regulations or the presence of a small number of patients (e.g., rare diseases). To address this data scarcity and to improve the situation, novel generative models such as Generative Adversarial Networks (GANs) have been widely used to generate synthetic data that mimic real data by representing features that reflect health-related information without reference to real patients. In this paper, we consider several GAN models to generate synthetic data used for training binary (malignant/benign) classifiers, and compare their performances in terms of classification accuracy with cases where only real data are considered. We aim to investigate how synthetic data can improve classification accuracy, especially when a small amount of data is available. To this end, we have developed and implemented an evaluation framework where binary classifiers are trained on extended datasets containing both real and synthetic data. The results show improved accuracy for classifiers trained with generated data from more advanced GAN models, even when limited amounts of original data are available.

The modern paradigms of machine learning algorithms and artificial intelligence base their success on processing a large quantity of data. Nevertheless, data does not come for free, and it can sometimes be practically unfeasible to collect enough data to train machine learning models successfully. That is the main reason why synthetic data generation is of great interest in the research community. Generating realistic synthetic data can empower machine learning models with vast datasets that are difficult to collect in the real world. In autonomous vehicles, it would require thousands of hours of driving recording for a machine learning model to learn how to drive a car in a safety-critical and effective way. The use of synthetic data, on the other hand, make it possible to simulate many different driving scenarios at a much lower cost. This thesis investigates the functioning of Meta-Sim, a synthetic data generator used to create datasets by learning from the real world. I evaluated the effects of replacing the stem of the Inception-V3 with the stem of the Inception- V4 as the feature extractor needed to process image data. Results showed similar behaviour of models that used the stem of the Inception-V4 instead of the Inception-V3. Slightly differences were found when the model tried to simulate more complex images. In these cases, the models that use the stem of the Inception-V4 converged in fewer iterations than those that used the Inception-V3, demonstrating superior behaviours of the Inception-V4. In the end, I proved that the Inception-V4 could be used to achieve state-of-the- art results in synthetic data generation. Moreover, in specific cases, I show that the Inception-V4 can exceed the performance attained by Meta-Sim. The outcome suggests further research in the field to validate the results on a larger scale. / De moderna paradigmen för algoritmer för maskininlärning och artificiell intelligens bygger sin framgång på att bearbeta en stor mängd data. Data är dock inte gratis, och det kan ibland vara praktiskt omöjligt att samla in tillräckligt med data för att träna upp maskininlärningsmodeller på ett framgångsrikt sätt. Det är huvudskälet till att generering av syntetiska data är av stort intresse för forskarsamhället. Genom att generera realistiska syntetiska data kan maskininlärningsmodeller få tillgång till stora datamängder som är svåra att samla in i den verkliga världen. I autonoma fordon skulle det krävas tusentals timmars körning för att en maskininlärningsmodell ska lära sig att köra en bil på ett säkerhetskritiskt och effektivt sätt. Användningen av syntetiska data gör det å andra sidan möjligt att simulera många olika körscenarier till en mycket lägre kostnad. I den här avhandlingen undersöks hur Meta-Sim fungerar, en generator för syntetiska data som används för att skapa dataset genom att lära sig av den verkliga världen. Jag utvärderade effekterna av att ersätta stammen från Inception-V3 med stammen från Inception-V4 som den funktionsextraktor som behövs för att bearbeta bilddata. Resultaten visade ett liknande beteende hos modeller som använde stammen från Inception-V4 i stället för Inception- V3. Små skillnader konstaterades när modellen försökte simulera mer komplexa bilder. I dessa fall konvergerade de modeller som använde Inception-V4:s stam på färre iterationer än de som använde Inception-V3, vilket visar att Inception- V4:s beteende är överlägset. I slutändan bevisade jag att Inception-V4 kan användas för att uppnå toppmoderna resultat vid generering av syntetiska data. Dessutom visar jag i specifika fall att Inception-V4 kan överträffa den prestanda som uppnås av Meta-Sim. Resultatet föreslår ytterligare forskning på området för att validera resultaten i större skala.

A brief overview of electrocardiogram (ECG) properties and the characteristics of various cardiac conditions is given. Two different models are used to generate synthetic ECG signals. Domain knowledge is used to create synthetic examples of 16 different heart beat types with these models. Other techniques for synthesizing ECG signals are explored. Various machine learning models with different combinations of real and synthetic data are used to classify individual heart beats. The performance of the different methods and models are compared, and synthetic data is shown to be useful in beat classification.

This thesis introduces a financial simulation model covering two related financial domains: Mobile Payments and Retail Stores systems.   The problem we address in these domains is different types of fraud. We limit ourselves to isolated cases of relatively straightforward fraud. However, in this thesis the ultimate aim is to introduce our approach towards the use of computer simulation for fraud detection and its applications in financial domains. Fraud is an important problem that impact the whole economy. Currently, there is a lack of public research into the detection of fraud. One important reason is the lack of transaction data which is often sensitive. To address this problem we present a mobile money Payment Simulator (PaySim) and Retail Store Simulator (RetSim), which allow us to generate synthetic transactional data that contains both: normal customer behaviour and fraudulent behaviour.    These simulations are Multi Agent-Based Simulations (MABS) and were calibrated using real data from financial transactions. We developed agents that represent the clients and merchants in PaySim and customers and salesmen in RetSim. The normal behaviour was based on behaviour observed in data from the field, and is codified in the agents as rules of transactions and interaction between clients and merchants, or customers and salesmen. Some of these agents were intentionally designed to act fraudulently, based on observed patterns of real fraud. We introduced known signatures of fraud in our model and simulations to test and evaluate our fraud detection methods. The resulting behaviour of the agents generate a synthetic log of all transactions as a result of the simulation. This synthetic data can be used to further advance fraud detection research, without leaking sensitive information about the underlying data or breaking any non-disclose agreements.   Using statistics and social network analysis (SNA) on real data we calibrated the relations between our agents and generate realistic synthetic data sets that were verified against the domain and validated statistically against the original source.   We then used the simulation tools to model common fraud scenarios to ascertain exactly how effective are fraud techniques such as the simplest form of statistical threshold detection, which is perhaps the most common in use. The preliminary results show that threshold detection is effective enough at keeping fraud losses at a set level. This means that there seems to be little economic room for improved fraud detection techniques.   We also implemented other applications for the simulator tools such as the set up of a triage model and the measure of cost of fraud. This showed to be an important help for managers that aim to prioritise the fraud detection and want to know how much they should invest in fraud to keep the loses below a desired limit according to different experimented and expected scenarios of fraud.

Many venture capitalists (VCs) use the “VC method” of valuation where they use judgment to estimate a probability of successful exit while determining the ownership share to demand in exchange for investing in a venture. However, prior models are not aligned with the “VC method” because they do not consider private information about entrepreneurial characteristics, the primary drivers of the above probability, and consequently do not model judgment. The three main chapters of this thesis—one theoretical, one simulation, and one empirical study—examine the venture capital deal process in sync with the “VC method.” Chapter 2 is theoretical and develops a principal-agent model of venture capital deal process incorporating double-sided moral hazard and one-sided private information. The VC is never fully informed about the entrepreneur’s disutility of effort in spite of due diligence checks, so takes on a belief about the latter’s performance in the funded venture to determine the offer. This study suggests that there exists a critical point in the VC’s belief—and correspondingly in the VC’s ownership share—that maximizes the total return to the two parties. It also uncovers optimal revision strategies for the VC to adopt if the offer is rejected where it is shown that the VC should develop a strong advisory capacity and minimize time constraints to facilitate investment. Chapter 3 simulates venture capital deals as per the theoretical model and confirms the existence of critical points in the VC’s belief and ownership share that maximize the returns to the two parties and their total return. Particularly, the VC’s return (in excess of his or her return from an alternate investment) peaks for a moderate ownership share for the VC. Since private information with the entrepreneur would preclude the VC from knowing these critical points a priori, the VC should demand a moderate ownership share to stay close to such a peak. Using data from simulations, we also generate predictions about the properties of the venture capital deal space—notably: (a) Teamwork is crucial to financing; and (b) If the VC is highly confident about the entrepreneur’s performance, it would work to the latter’s advantage. Chapter 4 reports the results from our survey of eight seasoned VCs affiliated with seven firms operating in Canada, USA, and UK, where our findings received a high degree of support.

Many venture capitalists (VCs) use the “VC method” of valuation where they use judgment to estimate a probability of successful exit while determining the ownership share to demand in exchange for investing in a venture. However, prior models are not aligned with the “VC method” because they do not consider private information about entrepreneurial characteristics, the primary drivers of the above probability, and consequently do not model judgment. The three main chapters of this thesis—one theoretical, one simulation, and one empirical study—examine the venture capital deal process in sync with the “VC method.” Chapter 2 is theoretical and develops a principal-agent model of venture capital deal process incorporating double-sided moral hazard and one-sided private information. The VC is never fully informed about the entrepreneur’s disutility of effort in spite of due diligence checks, so takes on a belief about the latter’s performance in the funded venture to determine the offer. This study suggests that there exists a critical point in the VC’s belief—and correspondingly in the VC’s ownership share—that maximizes the total return to the two parties. It also uncovers optimal revision strategies for the VC to adopt if the offer is rejected where it is shown that the VC should develop a strong advisory capacity and minimize time constraints to facilitate investment. Chapter 3 simulates venture capital deals as per the theoretical model and confirms the existence of critical points in the VC’s belief and ownership share that maximize the returns to the two parties and their total return. Particularly, the VC’s return (in excess of his or her return from an alternate investment) peaks for a moderate ownership share for the VC. Since private information with the entrepreneur would preclude the VC from knowing these critical points a priori, the VC should demand a moderate ownership share to stay close to such a peak. Using data from simulations, we also generate predictions about the properties of the venture capital deal space—notably: (a) Teamwork is crucial to financing; and (b) If the VC is highly confident about the entrepreneur’s performance, it would work to the latter’s advantage. Chapter 4 reports the results from our survey of eight seasoned VCs affiliated with seven firms operating in Canada, USA, and UK, where our findings received a high degree of support.