Reddit's Self-Organised Bull Runs

Semenova, Valentina and Winkler, Julian (2021): Reddit's Self-Organised Bull Runs.

Abstract

This paper develops an empirical and theoretical case for how `hype' among retail investors can drive large asset fluctuations. We use text data from discussions on WallStreetBets (WSB), an online investor forum with over eleven million followers as of February 2022, to demonstrate how the adoption of trading strategies spreads among retail investors. Using sentiment analysis, we document that WSB users adopt price predictions about assets (bullish or bearish) in part due to the sentiments expressed by their peers. We, furthermore, document evidence that asset discussions on WSB are self-perpetuating: an initial set of investors in a stock attracts a growing number of followers -- a pattern reminiscent of an epidemiological setting. Leveraging these findings, we develop a theoretical case for the impact of social dynamics among retail investors on asset prices. Our framework helps identify components of asset demand stemming from social dynamics, which we predict using WSB data. Our predictions explain significant variation in stock market activity; a consequential result is that weekly changes in sentiments and stock-specific discussions explain 16% of variance in the percent change of nominal trading volumes, within stocks. These findings emphasise the role that social dynamics play in financial markets, amplified by online social media.

• Item Type: MPRA Paper
• Language: English
• Keywords: Network Economics, Opinion Dynamics, Natural Language Processing, Behavioral Finance
• Subjects: D - Microeconomics > D8 - Information, Knowledge, and Uncertainty > D85 - Network Formation and Analysis: Theory; G - Financial Economics > G1 - General Financial Markets > G14 - Information and Market Efficiency ; Event Studies ; Insider Trading

References

Anderson, C. A., Lepper, M. R. & Ross, L. (1980), ‘Perseverance of social theories: The role of explanation in the persistence of discredited information.’, Journal of personality and social psychology 39(6), 1037.

Angrist, J. D. (2014), ‘The perils of peer effects’, Labour Economics 30, 98–108.

Araci, D. (2019), ‘Finbert: Financial sentiment analysis with pre-trained language models’, arXiv preprint arXiv:1908.10063.

Aral, S., Muchnik, L. & Sundararajan, A. (2009), ‘Distinguishing influence-based contagion from homophily-driven diffusion in dynamic networks’, Proceedings of the National Academy of Sciences 106(51), 21544–21549.

Aral, S. & Nicolaides, C. (2017), ‘Exercise contagion in a global social network’, Nature communications 8(1), 1–8.

Avery, C. & Zemsky, P. (1998), ‘Multidimensional uncertainty and herd behavior in financial markets’, American economic review pp. 724–748.

Bailey, M., Cao, R., Kuchler, T. & Stroebel, J. (2016), Social networks and housing markets, Technical report, National Bureau of Economic Research.

Banerjee, A., Chandrasekhar, A. G., Duflo, E. & Jackson, M. O. (2013), ‘The diffusion of microfinance’, Science 341(6144).

Banerjee, A. V. (1993), ‘The economics of rumours’, The Review of Economic Studies 60(2), 309–327.

Barberis, N. C. (2013), ‘Thirty years of prospect theory in economics: A review and assessment’, Journal of Economic Perspectives 27(1), 173–96.

Barlevy, G. & Veronesi, P. (2000), ‘Information acquisition in financial markets’, The Review of Economic Studies 67(1), 79–90.

Bifulco, R., Fletcher, J. M. & Ross, S. L. (2011), ‘The effect of classmate characteristics on post-secondary outcomes: Evidence from the add health’, American Economic Journal: Economic Policy 3(1), 25–53.

Black, F. (1986), ‘Noise’, The journal of finance 41(3), 528–543.

Blume, L. E., Brock, W. A., Durlauf, S. N. & Ioannides, Y. M. (2011), Identification of social interactions, in ‘Handbook of social economics’, Vol. 1, Elsevier, pp. 853–964.

Bollen, J., Mao, H. & Zeng, X. (2011), ‘Twitter mood predicts the stock market’, Journal of Computational Science 2(1), 1 – 8.

Bordalo, P., Gennaioli, N. & Shleifer, A. (2012), ‘Salience theory of choice under risk’, The Quarterly journal of economics 127(3), 1243–1285.

Bordalo, P., Gennaioli, N. & Shleifer, A. (2019), Diagnostic expectations and stock returns’, The Journal of Finance 74(6), 2839–2874.

Bordalo, P., Gennaioli, N. & Shleifer, A. (2020), ‘Memory, Attention, and Choice*’, The Quarterly Journal of Economics 135(3), 1399–1442.

Bouchaud, J.-P. (2013), ‘Crises and collective socioeconomic phenomena: simple models and challenges’, Journal of Statistical Physics 151(3), 567–606.

Bramoull ́e, Y., Djebbari, H. & Fortin, B. (2020), ‘Peer effects in networks: A survey’, Annual Review of Economics 12, 603–629.

Breza, E. & Chandrasekhar, A. G. (2019), ‘Social networks, reputation, and commitment: evidence from a savings monitors experiment’, Econometrica 87(1), 175–216.

Brock, W. A. & Durlauf, S. N. (2001), ‘Discrete choice with social interactions’, The Review of Economic Studies 68(2), 235–260.

Bulow, J. I., Geanakoplos, J. D. & Klemperer, P. D. (1985), ‘Multimarket oligopoly: Strategic substitutes and complements’, Journal of Political economy 93(3), 488–511.

Bursztyn, L., Ederer, F., Ferman, B. & Yuchtman, N. (2014), ‘Understanding mechanisms underlying peer effects: Evidence from a field experiment on financial decisions.’, Econometrica 82(4), 1273.

Chohan, U. W. (2021), ‘Counter-hegemonic finance: The Gamestop short squeeze’, Available at SSRN.

Cont, R. & Bouchaud, J.-P. (2000), ‘Herd behavior and aggregate fluctuations in financial markets’, Macroeconomic Dynamics 4(2), 170–196.

De Bondt, W. F. & Thaler, R. (1985), ‘Does the stock market overreact?’, The Journal of finance 40(3), 793–805.

De Long, J. B., Shleifer, A., Summers, L. H. & Waldmann, R. J. (1990), ‘Noise trader risk in financial markets’, Journal of political Economy 98(4), 703–738.

Devlin, J., Chang, M.-W., Lee, K. & Toutanova, K. (2018), ‘Bert: Pre-training of deep bidirectional transformers for language understanding’, arXiv preprint arXiv:1810.04805.

Duflo, E., Dupas, P. & Kremer, M. (2011), ‘Peer effects, teacher incentives, and the impact of tracking: Evidence from a randomized evaluation in Kenya’, American Economic Review 101(5), 1739–74.

Epple, D. & Romano, R. E. (2011), Peer effects in education: A survey of the theory and evidence, in ‘Handbook of social economics’, Vol. 1, Elsevier, pp. 1053–1163.

Garcia, D. (2013), ‘Sentiment during recessions’, The Journal of Finance 68(3), 1267–1300.

Gennaioli, N. & Shleifer, A. (2010), ‘What comes to mind’, The Quarterly journal of economics 125(4), 1399–1433.

Gennaioli, N. & Shleifer, A. (2018), A crisis of beliefs, Princeton University Press.

Gentzkow, M., Kelly, B. & Taddy, M. (2019), ‘Text as data’, Journal of Economic Literature 57(3), 535–74.

Grossman, S. J. & Stiglitz, J. E. (1980), ‘On the impossibility of informationally efficient markets’, The American economic review 70(3), 393–408.

Hellwig, C. & Veldkamp, L. (2009), ‘Knowing what others know: Coordination motives in information acquisition’, The Review of Economic Studies 76(1), 223–251.

Hirshleifer, D. (2001), ‘Investor psychology and asset pricing’, The journal of Finance 56(4), 1533–1597.

Hommes, C. (2013), Behavioral Rationality and Heterogeneous Expectations in Complex Economic Systems, Cambridge University Press.

Hommes, C. (2021), ‘Behavioral and experimental macroeconomics and policy analysis: A complex systems approach’, Journal of Economic Literature 59(1), 149–219.

Kahneman, D. & Tversky, A. (1972), ‘Subjective probability: A judgment of representativeness’, Cognitive psychology 3(3), 430–454.

Kahneman, D. & Tversky, A. (1973), ‘On the psychology of prediction.’, Psychological review 80(4), 237.

Kahneman, D. & Tversky, A. (1979), ‘Prospect theory: An analysis of decision under risk’, Econometrica 47(2), 263–291.

Kirman, A. (1993), ‘Ants, rationality, and recruitment’, The Quarterly Journal of Economics 108(1), 137–156.

Kumar, A. & Lee, C. M. (2006), ‘Retail investor sentiment and return comovements’, The Journal of Finance 61(5), 2451–2486.

Lahno, A. M. & Serra-Garcia, M. (2015), ‘Peer effects in risk taking: Envy or conformity?’, Journal of Risk and Uncertainty 50(1), 73–95.

MacKinnon, J. G. & White, H. (1985), ‘Some heteroskedasticity-consistent covariance matrix estimators with improved finite sample properties’, Journal of Econometrics 29(3), 305–325.

Patacchini, E. & Zenou, Y. (2016), ‘Social networks and parental behavior in the intergenerational transmission of religion’, Quantitative Economics 7(3), 969–995.

Ross, L., Lepper, M. R. & Hubbard, M. (1975), ‘Perseverance in self-perception and social perception: biased attributional processes in the debriefing paradigm.’, Journal of personality and social psychology 32(5), 880.

Sabherwal, S., Sarkar, S. K. & Zhang, Y. (2011), ‘Do internet stock message boards influence trading? evidence from heavily discussed stocks with no fundamental news’, Journal of Business Finance & Accounting 38(9-10), 1209–1237.

Sacerdote, B. (2011), Peer effects in education: How might they work, how big are they and how much do we know thus far?, in ‘Handbook of the Economics of Education’, Vol. 3, Elsevier, pp. 249–277.

Securities & Commission, E. (1963), ‘Report of special study of securities markets of the securities and exchange commission’, House Document 95(4).

Shefrin, H. & Statman, M. (1994), ‘Behavioral capital asset pricing theory’, Journal of financial and quantitative analysis 29(3), 323–349.

Shiller, R. J. (1984), Stock prices and social dynamics, Technical Report 2, The Brookings Institution.

Shiller, R. J. (2005), Irrational Exuberance: (Second Edition), Princeton University Press.

Shiller, R. J. (2014), ‘Speculative asset prices’, American Economic Review 104(6), 1486–1517.

Shiller, R. J. (2017), ‘Narrative economics’, American Economic Review 107(4), 967–1004.

Shleifer, A. & Summers, L. H. (1990), ‘The noise trader approach to finance’, Journal of Economic perspectives 4(2), 19–33.

Tetlock, P. C. (2007), ‘Giving content to investor sentiment: The role of media in the stock market’, The Journal of finance 62(3), 1139–1168.

Tucker, J. A., Guess, A., Barber ́a, P., Vaccari, C., Siegel, A., Sanovich, S., Stukal, D. & Nyhan, B. (2018), ‘Social media, political polarization, and political disinformation: A review of the scientific literature’, Political polarization, and political disinformation: a review of the scientific literature (March 19, 2018) .

Vasileiou, E., Bartzou, E. & Tzanakis, P. (2021), ‘Explaining Gamestop short squeeze using intraday data and Google searches.’, Available at SSRN 3805630.

Wang, Y.-H., Keswani, A. & Taylor, S. J. (2006), ‘The relationships between sentiment, returns and volatility’, International Journal of Forecasting 22(1), 109–123.

Yan, X., Guo, J., Lan, Y. & Cheng, X. (2013), A biterm topic model for short texts, in ‘Proceedings of the 22nd International Conference on World Wide Web’, WWW ’13, Association for Computing Machinery, New York, NY, USA, p. 1445–1456.

Zenou, Y. (2016), ‘Key players’, The Oxford Handbook of the Economics of Networks 11.