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- Working Paper
Index Rebalancing and Stock Market Composition: Do Indexes Time the Market?
By: Marco Sammon and John J. Shim
Value-weighted indexes must rebalance in response to stock market composition changes, e.g., issuance, buybacks, and IPOs. In doing so, existing index funds implicitly engage in market timing. Index funds’ long-short rebalancing portfolios have a -3.5% annual return... View Details
- May 2025
- Case
First Citizens’ Acquisition of SVB
- April 2025
- Article
The Disappearing Index Effect
By: Robin Greenwood and Marco Sammon
The abnormal return associated with a stock being added to the S&P 500 has fallen from an average
of 7.4% in the 1990s to 0.3% over the past decade. This has occurred despite a significant increase in the
share of stock market assets linked to the index. A similar... View Details
- January 2025
- Teaching Note
Big Media's Game of Thrones
By: Emily McComb, Marco Sammon and James Barnett
Teaching Note for HBS Case No. 224-045. View Details
- January 2025
- Teaching Note
Index and Active Investing: Vanguard and the New Frontier of Active ETFs
By: Marco Sammon and Luis M. Viceira
- January 2025
- Case
Index and Active Investing: Vanguard and the New Frontier of Active ETFs
By: Marco Sammon, Luis M. Viceira and Jonathan Kanagasabai
This case explores Vanguard’s strategic decision-making process as it considers entering the growing market for actively managed exchange-traded funds (ETFs). Set in 2024, the case places students in the position of Rodney Comegys, Vanguard’s global head of the Equity... View Details
- January 2025
- Technical Note
Technical Note on Mutual Funds and Exchange Traded Funds (ETFs)
By: Marco Sammon, Luis M. Viceira and Jonathan Kanagasabai
- 2024
- Working Paper
Categorical Processing in a Complex World
By: Marco Sammon, Thomas Graeber and Christopher Roth
In real-world news environments, quantitative information is rarely presented in isolation; it is characterized through qualitative comparisons with various reference levels. Company earnings, for example, are commonly compared to analyst forecasts, previous earnings,... View Details
- 2024
- Working Paper
Primary Capital Market Transactions and Index Funds
By: Marco Sammon and Chris Murray
We document the effects of mechanical buying by CRSP-index-tracking funds on post-IPO returns and IPO deal structure. Leveraging a difference-in-differences-style design built on a 2017 CRSP rule change, we find that expected index fund demand leads fast track IPOs to... View Details
- 2024
- Working Paper
Who Clears the Market When Passive Investors Trade?
By: Marco Sammon and John J. Shim
We find that firms are the primary sellers of shares when index funds are net buyers, providing shares at a nearly one-for-one rate. Rather than provide liquidity, most demand-side institutions trade in the same direction as index funds, especially over long horizons.... View Details
- July 2024
- Article
The Passive-Ownership Share Is Double What You Think It Is
By: Alex Chinco and Marco Sammon
Each time a stock gets added to or dropped from a benchmark index, we ask: “How much money would have to be tracking that index to explain the huge spike in rebalancing volume we observe on reconstitution day?” While index funds held 16% of the US stock market in 2021,... View Details
- September 2023
- Article
Customer Churn and Intangible Capital
By: Scott R. Baker, Brian Baugh and Marco Sammon
Intangible capital is a crucial and growing piece of firms’ capital structure, but many of its distinct components are difficult to measure. We develop and make available several new firm-level metrics regarding a key component of intangible capital – firms’ customer... View Details
- 2023
- Working Paper
Do Active Funds Do Better in What They Trade?
By: Marco Sammon and John J. Shim
We develop two new, simple measures to quantify active fund decisions at the individual position level. The intuition is to separate passive rebalancing induced by flows and position changes from active rebalancing decisions. We find that additive active rebalancing --... View Details
- 2024
- Working Paper
The Retail Habitat
By: Toomas Laarits and Marco Sammon
Retail investors trade hard-to-value stocks. Controlling for size, stocks with a high share of retail-initiated trades are composed of more intangible capital, have longer duration cash-flows and a higher likelihood of being mispriced. Consistent with retail-heavy... View Details
Keywords: Retail; Retail Trade; Intangible Capital; Mispricing; Investment; Valuation; Business Earnings
- 2022
- Working Paper
Retail Investors’ Contrarian Behavior Around News, Attention, and the Momentum Effect
By: Cheng (Patrick) Luo, Enrichetta Ravina, Marco Sammon and Luis M. Viceira
Using a large panel of U.S. brokerage accounts trades and positions, we show that a large fraction of retail investors trade as contrarians after large earnings surprises, especially for loser stocks, and that such contrarian trading contributes to post earnings... View Details
- 2024
- Working Paper
What Triggers National Stock Market Jumps?
By: Scott R. Baker, Nicholas Bloom, Steven J. Davis and Marco Sammon
We examine newspapers the day after major stock-market jumps to evaluate the proximate cause, geographic source, and clarity of these events from 1900 in the US, 1930 in the UK and 1980 in 12 other countries. We find four main results. First, the United States plays an... View Details
- December 2021
- Article
Trade Policy Uncertainty and Stock Returns
By: Marcelo Bianconi, Federico Esposito and Marco Sammon
A recent literature has documented large real effects of trade policy uncertainty (TPU) on trade, employment, and investment, but there is little evidence that investors are compensated for bearing such risk. To quantify the risk premium associated with TPU, we exploit... View Details
- Article
The Unprecedented Stock Market Reaction to COVID-19
By: Scott Baker, Nicholas Bloom, Steven J. Davis, Kyle Kost, Marco Sammon and Tasaneeya Viratyosin
No previous infectious disease outbreak, including the Spanish Flu, has impacted the stock market as forcefully as the COVID-19 pandemic. In fact, previous pandemics left only mild traces on the U.S. stock market. We use text-based methods to develop these points with... View Details