1 the Predictive Power of Social Media Within Cryptocurrency Markets
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1 The Predictive Power of Social Media within Cryptocurrency Markets Ross Christopher Phillips A thesis submitted for the degree of Doctor of Philosophy Department of Computer Science University College London February 2019 I, Ross Christopher Phillips, confirm that the work presented in this thesis is my own. Where information has been derived from other sources, I confirm that this has been indicated in the thesis. 1 Abstract Blockchain technology has generated a great deal of interest in recent years, as has the associated area of cryptocurrency trading, not only on the part of individuals but also from traditional financial institutions and hedge funds. However, there is currently limited knowledge as to how to predict future cryptocurrency price movements. This thesis investigates whether online indicators, especially from social media, can be harnessed to predict cryptocurrency price movements – to achieve this, three experiments are conducted. The first experiment analyses time-evolving relationships between chosen online indicators and associated cryptocurrency prices; relationships are considered over short, medium and long-term durations. The work introduces and evaluates several influential factors from the social media platform Reddit, a platform previously unexplored within cryptocurrency prediction literature. It is found that medium and longer-term relationships strengthen in bubble market regimes (compared to non-bubble regimes). The second experiment utilises these promising new factors as inputs to a predictive model. The model used was originally designed to detect influenza epidemic outbreaks, and is repurposed here to model epidemic-like cryptocurrency price bubbles, demonstrating how social media can be used to track the epidemic spread of an investment idea. The predictive power of the model is validated through the generation of a profitable trading strategy. Having considered quantitative count-based metrics in the previous chapters (e.g. posts per day, submissions per day, new authors per day etc.), the next experiment considers the content of social media submissions. More specifically, the third experiment analyses social media submission content to investigate whether certain topics of discussion precede upcoming shorter term (positive or negative) price movements. Information evidencing time-varying interest in various topics is retrieved from social media submissions, upon which hidden interactions with the associated cryptocurrency price are deciphered. It is found that certain topics precede major positive or negative price movements, and also additional analysis shows that certain discussion topics exhibit longer-term relationships with cryptocurrency market prices. 2 Impact statement Cryptocurrencies and related blockchain technology have recently experienced an explosion in interest, not only from within academia and industry—the area has also become topical mainstream news. Due to this rapidly increasing interest from all angles, the work presented here has the potential to be significantly impactful in a wide range of areas. The work provides several benefits within academia. Firstly, this work provides a foundation, in the relatively unexplored academic area of cryptocurrency price and bubble prediction, upon which further academic work could be undertaken; proposals for such extensions are provided. Secondly, the work presents a new and unexplored data source (Reddit) as a valuable source of information in cryptocurrency-related prediction. Thirdly, the work contributes to longer standing epidemic-based speculative asset bubble literature, demonstrating, in an area where data is usually hard to source, how social media can track the spread of an investment idea. Outside of academia, there has been a flurry of activity in the cryptocurrency and blockchain area from a range of entities, including central banks, trading institutions and technology companies. The techniques for predicting price movements contained in this thesis could aid central banks to design and track their own cryptocurrencies and aid private companies in their timely purchase of cryptocurrencies, either for resale profit or for accumulation for later use of associated blockchain technology. Furthermore, the ability discovered here to detect if a speculative bubble is occurring may provide a warning to non-professional investors that any observed price rises may be the result of a (potentially unsustainable) bubble. By design, the use of cryptocurrencies is not limited to one geographical area or jurisdiction. This inherently global nature of cryptocurrencies results in a global impact for this research. The academic impact of the research is brought about through dissemination in scholarly journals and conference proceedings. When available, a peer-reviewed open-access journal is chosen to allow the most effective and accessible dissemination. The publication of the work is also complemented by presentations in a range of contexts (for example, conference and internal presentations, and in an interview with a cryptocurrency news website). 3 Acknowledgements I would like to express my gratitude to my supervisor, Dr. Denise Gorse, for her guidance, unfailing availability and scientific wisdom throughout the PhD. I appreciate her encouragement to follow my interests, especially given that cryptocurrency analytic research was a relatively new academic area when I commenced my research. I hope that Denise’s mastery of English grammar has worn off on me, at least slightly, through her detailed improvements of my texts. I am also thankful to the examiners of my PhD transfer viva, Prof. Tomaso Aste and Dr. Paolo Tasca. Their insightful recommendations, given their areas of expertise, provided important finishing touches and contributed towards a more robust final thesis. In addition I would like to acknowledge the academic, financial and industrial support provided by the Financial Computing and Analytics Centre for Doctoral Training and, more broadly, University College London. Finally, but by no means least, I would like to express my appreciation to Julia, Paul and Rachael. Their unequivocal support and encouragement, not only during the PhD, will always be appreciated. 4 Contents 1 Introduction ............................................................................................................................... 10 1.1 Motivation for this research ................................................................................................ 10 1.2 Research objectives ............................................................................................................. 14 1.3 Thesis structure ................................................................................................................... 16 1.4 Related publications ............................................................................................................ 16 2 Background and Literature Review .......................................................................................... 18 2.1 An introduction to cryptocurrencies ................................................................................... 18 2.2 Cryptocurrency trading markets ......................................................................................... 29 2.3 Use of online indicators in cryptocurrency price prediction ............................................... 33 3 Data Sources and Acquisition ................................................................................................... 39 3.1 Choice of social media data sources ................................................................................... 39 3.2 An introduction to Reddit ................................................................................................... 44 3.3 Data acquisition .................................................................................................................. 46 3.4 Preliminary factor derivation and data analysis .................................................................. 52 4 Cryptocurrency Price Drivers: Wavelet Coherence Analysis Revisited .................................. 63 4.1 Background and related work ............................................................................................. 64 4.2 Methodology ....................................................................................................................... 67 4.3 Results: Coherence between cryptocurrencies and online factors ...................................... 73 4.4 Results: Coherence between different cryptocurrencies ..................................................... 84 4.5 Discussion ........................................................................................................................... 86 5 Predicting Cryptocurrency Price Bubbles using Social Media Data and Epidemic Modelling 89 5.1 Background and related work ............................................................................................. 90 5 5.2 Methodology ....................................................................................................................... 94 5.3 Results ............................................................................................................................... 103 5.4 Discussion ......................................................................................................................... 110 6 Mutual-Excitation of Cryptocurrency Market Returns and Social