Research
Lo, Andrew W., and Alexander Remorov (2017), Stop-Loss Strategies with Serial Correlation, Regime Switching, and Transaction Costs, Journal of Financial Markets 34, 1–15.
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Stop-loss strategies are commonly used by investors to reduce their holdings in risky assets if prices or total wealth breach certain pre- specified thresholds. We derive closed-form expressions for the impact of stop-loss strategies on asset returns that are serially correlated, regime switching, and subject to transaction costs. When applied to a large sample of individual U.S. stocks, we show that tight stop-loss strategies tend to under-perform the buy-and-hold policy in a mean-variance frame work due to excessive trading costs. Outperformance is possible for stocks with sufficiently high serial correlation in returns. Certain strategies succeed at reducing downside risk, but not substantially.
Lo, Andrew W. (2017), Discussion: New Directions for the FDA in the 21st Century, Biostatistics 18 (3), 404–407.
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The Food and Drug Administration (FDA) is a remarkable agency, one of the crown jewels of the US government. Its staff and structure are dedicated to safeguarding American public health, and although we sometimes complain about its role as gatekeeper, we all sleep better knowing that our foods and drugs have passed the FDA’s careful scrutiny. Its regulatory scope and process reflect the technical demands of its responsibilities, and the FDA is one of the very few federal agencies that have taken a lead in defining and developing the new field of regulatory science
Lo, Andrew W. (2017), Moore’s Law vs. Murphy’s Law in the Financial System: Who’s Winning?, Journal of Investment Management 15 (1), 17–38.
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Breakthroughs in computing hardware, software, telecommunications, and data analytics have transformed the financial industry, enabling a host of new products and services such as automated trading algorithms, crypto-currencies, mobile banking, crowdfunding, and robo-advisors. However, the unintended consequences of technology-leveraged finance include firesales, flash crashes, botched initial public offerings, cybersecurity breaches, catastrophic algorithmic trading errors, and a technological arms race that has created new winners, losers, and systemic risk in the financial ecosystem. These challenges are an unavoidable aspect of the growing importance of finance in an increasingly digital society. Rather than fighting this trend or forswearing technology, the ultimate solution is to develop more robust technology capable of adapting to the foibles in human behavior so users can employ these tools safely, effectively, and effortlessly. Examples of such technology are provided.
Lo, Andrew W. (2002), The Statistics of Sharpe Ratios, Financial Analysts Journal 58 (4), 36–52.
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The building blocks of the Sharpe ratio—expected returns and volatilities— are unknown quantities that must be estimated statistically and are, therefore, subject to estimation error. This raises the natural question: How accurately are Sharpe ratios measured? To address this question, I derive explicit expressions for the statistical distribution of the Sharpe ratio using standard asymptotic theory under several sets of assumptions for the return-generating process—independently and identically distributed returns, stationary returns, and with time aggregation. I show that monthly Sharpe ratios cannot be annualized by multiplying by except under very special circumstances, and I derive the correct method of conversion in the general case of stationary returns. In an illustrative empirical example of mutual funds and hedge funds, I find that the annual Sharpe ratio for a hedge fund can be overstated by as much as 65 percent because of the presence of serial correlation in monthly returns, and once this serial correlation is properly taken into account, the rankings of hedge funds based on Sharpe ratios can change dramatically.
Lo, Andrew W. (2001), Risk Management for Hedge Funds: Introduction and Overview, Financial Analysts Journal 57 (6), 16–33.
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Although risk management has been a well-plowed field in financial modeling for over two decades, traditional risk management tools such as mean-variance analysis, beta, and Value-at-Risk do not capture many of the risk exposures of hedge-fund investments. In this article, I review several aspects of risk management that are unique to hedge funds - survivorship bias, dynamic risk analytics, liquidity, and nonlinearities - and provide examples that illustrate their potential importance to hedge-fund managers and investors. I propose a research agenda for developing a new set of risk analytics specifically designed for hedge-fund investments, with the ultimate goal of creating risk transparency while, at the same time, protecting the proprietary nature of hedge-fund investment strategies.
Statistical Tests of Contingent-Claims Asset-Pricing Models: A New Methodology
Lo, Andrew W. (1986), Statistical Tests of Contingent-Claims Asset-Pricing Models: A New Methodology, Journal of Financial Economics 17 (1), 143–173.
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A new methodology for statistically testing contingent-claims asset-pricing models based on asymptotic statistical theory is proposed. It is introduced in the context of the Black-Scholes option-pricing model, for which some illustrative estimation, inference, and simulation results are also presented. The proposed methodology is then extended to arbitrary contingent claims by first considering the estimation problem for general Itô processes and then deriving the asymptotic distribution of a general contingent claim which depends upon such Itô processes.
Business Models to Cure Rare Disease: A Case Study of Solid Biosciences
Kim, Esther S., and Andrew W. Lo (2016), Business Models to Cure Rare Disease: A Case Study of Solid Biosciences, Journal of Investment Management 14 (4), 87–101.
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Duchenne muscular dystrophy (DMD) is a rare genetic disorder affecting thousands of individuals, mainly young males, worldwide. Currently, the disease has no cure, and is fatal in all cases. Advances in our understanding of the disease and innovations in basic science have recently allowed biotechnology companies to pursue promising treatment candidates for the disease, but so far, only one drug with limited application has achieved FDA approval. In this case study, we profile the work of an early-stage life sciences company, Solid Biosciences, founded by a father of a young boy with DMD. In particular, we discuss Solid’s one-disease focus and its strategy to treat the disease with a diversified portfolio of approaches. The company is currently building a product pipeline consisting of genetic interventions, small molecules and biologics, and assistive devices, each aimed at addressing a different aspect of DMD. We highlight the potential for Solid’s business model and portfolio to achieve breakthrough treatments for the DMD patient community.
Cao, Charles, Bing Liang, Andrew W. Lo, and Lubomir Petrasek (2018), Hedge Fund Holdings and Stock Market Efficiency, Review of Asset Pricing Studies 8 (1), 77–116.
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We examine the relation between changes in hedge fund equity holdings and measures of informational efficiency of stock prices derived from intraday transactions as well as daily data. On average, hedge fund ownership of stocks leads to greater improvements in price efficiency than mutual fund or bank ownership, especially for stocks held by hedge funds with high portfolio turnover and superior security selection skills. However, stocks held by hedge funds experienced large declines in price efficiency in the last quarter of 2008, particularly if the funds were connected to Lehman Brothers as a prime broker and used leverage in combination with lenient redemption terms.
Use of Bayesian Decision Analysis to Minimize Harm in Patient-Centered Randomized Clinical Trials in Oncology
Montazerhodjat, Vahid, Shomesh E. Chaudhuri, Daniel J. Sargent, and Andrew W. Lo (2017), Use of Bayesian Decision Analysis to Minimize Harm in Patient-Centered Randomized Clinical Trials in Oncology, JAMA Oncology 3 (9), e170123.
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There is general agreement in the biomedical community that the development of therapies for certain diseases should take priority. This ethic has motivated legislative initiatives, such as the Orphan Drug Act of 1983, and underpins several important innovations in regulatory approval processes, such as the US Food and Drug Administration’s (FDA) fast-track, breakthrough-therapy, accelerated-approval, and priority-review designations. However, none of these innovations directly address the critical issue of how to incorporate the patient’s perspective in deciding whether a drug candidate should be approved or not. The current approach in clinical trial design is to minimize the chance of ineffective treatment caused by a type 1 error, that is, a false-positive result. However, the arbitrary nature of the threshold for the probability of type 1 error, alpha, raises an ethical question about its justification. A 2.5% threshold may not be appropriate for terminal illnesses that have no effective therapies; such patients may prefer to take a bigger chance on a false-positive result, even if the likelihood of an effective therapy is small. To quote the noted biostatistician Donald Berry, “We should also focus on patient values, not just P values.”
Spectral Analysis of Stock-Return Volatility, Correlation, and Beta
Chaudhuri, Shomesh E., and Andrew W. Lo (2015), Spectral Analysis of Stock-Return Volatility, Correlation, and Beta, 2015 IEEE Signal Processing and Signal Processing Education Workshop (SP/SPE), 232–236.
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We apply spectral techniques to analyze the volatility and correlation of U.S. common-stock returns across multiple time horizons at the aggregate-market and individual-firm level. Using the cross-periodogram to construct frequency bandlimited measures of variance, correlation and beta, we find that volatilities and correlations change not only in magnitude over time, but also in frequency. Factors that may be responsible for these trends are proposed and their implications for portfolio construction are explored.