William Mullins

Assistant Professor of Finance Rady School, UC San Diego

Email: wmullins at ucsd dot edu cv bio GoogleScholar

Working papers

- Does Partisanship Shape Investor Beliefs? Evidence from the COVID-19 Pandemic

(with Tony Cookson and Joey Engelberg) SSRN link SocArXiv link pdf

Abstract: We use party-identifying language – like “Liberal Media” and “MAGA”– to identify Republican users on the investor social platform StockTwits. Using a difference-in-difference design, we find that the beliefs of partisan Republicans about equities remain relatively unfazed during the COVID-19 pandemic, while other users become considerably more pessimistic. In cross-sectional tests, we find Republicans become relatively more optimistic about stocks that suffered the most from COVID-19, but more pessimistic about Chinese stocks. Finally, stocks with the greatest partisan disagreement on StockTwits have significantly more trading in the broader market, which explains 20% of the increase in stock turnover during the pandemic.

Abstract: We find evidence of selective exposure to confirmatory information among 300,000 users on the investor social network StockTwits. Self-described bulls are 5 times more likely to follow a user with a bullish view of the same stock than self-described bears. This tendency is strong even among professional investors and is more pronounced on earnings announcement days. Placing oneself in an information “echo chamber” generates significant differences in the newsfeeds of bulls and bears: over a 50-day period, a bull will see 70 more bullish messages and 15 fewer bearish messages than a bear over the same period. Selective exposure creates “information silos” in which the diversity of received signals is high across users’ newsfeeds but is low within users’ newsfeeds. Finally, we show that this siloing of information is positively related to trading volume.

- Unconventional Monetary Policy and Bank Lending Relationships

(with Anne Duquerroy and Christophe Cahn) SSRN link SocArXiv link pdf

Best Paper Prize at the Colorado Finance Summit

Abstract: We explore how banks transmit central bank liquidity injections using unique variation in the ECB’s 2011-12 Very Long-Term Refinancing Operations (VLTROs) which affected lending to firms discontinuously across credit ratings (i.e., within banks). We show that banks transmit liquidity differently to multi-bank firms than to firms with only one bank. Single-bank firms receive longer-term relationship lending and increase investment, while multi-bank firms receive short-term transactions-style lending only. Policy effects are attributable to increasing the maturity of bank borrowing from the ECB in combination with allowing banks to use loans to firms as collateral for such borrowing

- Credit Guarantees and New Bank Relationships

(with Patricio Toro) pdf

Presented at: Finance UC International Conference, UC San Diego (Rady) Finance Seminar, Central Bank of Chile, Universidad de Chile, International Conference on Small Business Finance, Edinburgh Corporate Finance Conference, MIT Golub Center 4th Annual Conference, NBER Entrepreneurship, Chicago Financial Institutions Conference, and U. of Michigan Finance Seminar

Abstract: Government credit guarantees for bank loans direct vast volumes of credit and are the main policy tool used to improve firms' access to credit. This paper examines Chile’s credit guarantee scheme, which is similar to that of many OECD countries. Using a regression discontinuity design around the eligibility cutoff we find that guarantees more than double firms' borrowing without detectable increases in default rates. We also show that banks use guarantees to build new borrower relationships, an important and poorly understood process. The scheme also has an amplification effect: firms increase borrowing from other banks following a guarantee. Finally, we show that firms use the credit increase to significantly scale up their sales and employment. The fact that guarantees are not a common pool resource in this policy design is critical to understanding these results.

- The Governance Impact of Indexing: Evidence from Regression Discontinuity


Presented at: Georgetown, U. of Colorado (Boulder), University of Rochester, University of Maryland, Boston College, University of Michigan, London Business School, London School of Economics, Wharton. Invited, but did not present: NYU Stern, University of Washington (Seattle)


- How do CEOs see their roles? Management Philosophies and Styles in Family and non-Family Firms

(with Antoinette Schoar) Journal of Financial Economics (2016) SSRN link pdf Non-technical summary

Appendix 1; Survey Appendix; Appendix 2

Abstract: Using a survey of 800 Chief Executive Officers (CEOs) in 22 emerging economies, we show that CEOs' management styles and philosophies vary with the ownership and governance structure of their firms. Founders and CEOs of firms with greater family involvement display a greater stakeholder focus and feel more accountable to employees and banks than to shareholders. They also have a more hierarchical management approach, and see their role as maintaining the status quo rather than bringing about change. In contrast, CEOs of non-family firms emphasize shareholder-value-maximization. Finally, firm-level variation in ownership is as important in explaining management philosophies as cross-country or industry-level differences.