Economic shocks can have diverse effects on financial market dynamics at different time horizons, yet traditional portfolio management tools do not distinguish between short- and long-term components in alpha, beta, and covariance estimators. In this paper, we apply spectral analysis techniques to quantify stock-return dynamics across multiple time horizons.Using the Fourier transform, we decompose asset-return variances, correlations, alphas, and betas into distinct frequency components. These decompositions allow us to identify the relative importance of specific time horizons in determining each of these quantities, as well as to construct mean-variance-frequency optimal portfolios. Our approach can be applied to any portfolio, and is particularly useful for comparing the forecast power of multiple investment strategies. We provide several numerical and empirical examples to illustrate the practical relevance of these techniques.
with David Weinstock, The Boston Globe
"A new class of medications was recently approved that cures more than 95 percent of people with Hepatitis C in only six weeks at a cost of about $84,000 per person, and new therapies with price tags that are likely to exceed $1 million per person are now available or coming soon. How can patients possibly afford them?
"In an article published in the journal Science Translation Medicine, we outline a feasible market-based solution that could immediately expand access to transformative medications, including cures for Hepatitis C and cancer. The basic concept is to convert a large upfront medical expense into a series of more affordable payments, akin to getting a mortgage when buying a house. The challenge of curative medications that only require a short course of therapy is that the whole price is paid upfront — how many homeowners could buy their houses using only cash? Instead, most home buyers get a mortgage and make monthly payments for as long as they benefit from owning the house or until the full amount is paid. We propose the same solution to overcome the liquidity problem that prevents access to curative medications, which we call “health care loans,” or HCLs..."
with Vahid Montazerhodjat and David M. Weinstock, Science Translational Medicine 8(2016), 327ps6.
A crisis is building over the prices of new transformative therapies for cancer, hepatitis C virus infection, and rare diseases. The clinical imperative is to offer these therapies as broadly and rapidly as possible. We propose a practical way to increase drug affordability through health care loans (HCLs)—the equivalent of mortgages for large health care expenses. HCLs allow patients in both multipayer and single-payer markets to access a broader set of therapeutics, including expensive short-duration treatments that are curative. HCLs also link payment to clinical benefit and should help lower per-patient cost while incentivizing the development of transformative therapies rather than those that offer small incremental advances. Moreover, we propose the use of securitization—a well-known financial engineering method—to finance a large diversified pool of HCLs through both debt and equity. Numerical simulations suggest that securitization is viable for a wide range of economic environments and cost parameters, allowing a much broader patient population to access transformative therapies while also aligning the interests of patients, payers, and the pharmaceutical
Journal of Portfolio Management 42(2016), 21–36.
Technological advances in telecommunications, securities exchanges, and algorithmic trading have facilitated a host of new investment products that resemble theme-based passive indexes but which depart from traditional market-cap-weighted portfolios. I propose broadening the definition of an index using a functional perspective—any portfolio strategy that satisfies three properties should be considered an index: (1) it is completely transparent; (2) it is investable; and (3) it is systematic, i.e., it is entirely rules-based and contains no judgment or unique investment skill. Portfolios satisfying these properties that are not market-cap-weighted are given a new name: “dynamic indexes.” This functional definition widens the universe of possibilities and, most importantly, decouples risk management from alpha generation. Passive strategies can and should be actively risk managed, and I provide a simple example of how this can be achieved. Dynamic indexes also create new challenges of which the most significant is backtest bias, and I conclude with a proposal for managing this risk.
with Florentin Butaru, Qingqing Chen, Brian Clark, Sanmay Das, Akhtar Siddique, Journal of Banking and Finance 72(2016), 218–239.
Using account level credit-card data from six major commercial banks from January 2009 to December 2013, we apply machine-learning techniques to combined consumer-tradeline, credit-bureau, and macroeconomic variables to predict delinquency. In addition to providing accurate measures of loss probabilities and credit risk, our models can also be used to analyze and compare risk management practices and the drivers of delinquency across the banks. We find substantial heterogeneity in risk factors, sensitivities, and predictability of delinquency across banks, implying that no single model applies to all six institutions. We measure the efficacy of a bank’s risk-management process by the percentage of delinquent accounts that a bank manages effectively, and find that efficacy also varies widely across institutions. These results suggest the need for a more customized approached to the supervision and regulation of financial institutions, in which capital ratios, loss reserves, and other parameters are specified individually for each institution according to its credit-risk model exposures and forecasts.
Is the FDA Too Conservative or Too Aggressive?: A Bayesian Decision Analysis of Clinical Trial Design
with Leah Isakov and Vahid Montazerhodjat
Implicit in the drug-approval process is a trade-off between Type I and Type II error. We propose using Bayesian decision analysis (BDA) to minimize the expected cost of drug approval, where relative costs are calibrated using U.S. Burden of Disease Study 2010 data. The results for conventional fixed-sample randomized clinical-trial designs suggest that for terminal illnesses with no existing therapies such as pancreatic cancer, the standard thresh-old of 2.5% is too conservative; the BDA-optimal threshold is 27.9%. However, for relatively less deadly conditions such as prostate cancer, 2.5% may be too risk-tolerant or aggressive; the BDA-optimal threshold is 1.2%. We compute BDA-optimal sizes for 25 of the most lethal diseases and show how a BDA-informed approval process can incorporate all stakeholders’ views in a systematic, transparent, internally consistent, and repeatable manner.
Economic Policy Review 22(2016), 17–42.
Culture is a potent force in shaping individual and group behavior, yet it has received scant attention in the context of financial risk management and the recent financial crisis. I present a brief overview of the role of culture according to psychologists, sociologists, and economists, and then present a specific framework for analyzing culture in the context of financial practices and institutions in which three questions are answered: (1) What is culture?; (2) Does it matter?; and (3) Can it be changed? I illustrate the utility of this framework by applying it to five concrete situations—Long Term Capital Management; AIG Financial Products; Lehman Brothers and Repo 105; Société Générale’s rogue trader; and the SEC and the Madoff Ponzi scheme—and conclude with a proposal to change culture via “behavioral risk management.”
with Shomesh Chaudhuri, Signal Processing and Signal Processing Education Workshop (SP/SPE), 2015 IEEE, 232–236.
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.
with Gary P. Pisano, Sloan Management Review 57(2015), 47–57.
with Edward Jung, Project Syndicate
"As price-gouging practices by a handful of drug companies attract headlines, one troubling aspect of the story remains underplayed. Exorbitant increases in the prices of existing drugs, including generics, are motivated not just by crass profiteering but by a deep skepticism about the economic feasibility of developing new drugs. That skepticism is justified.
"Traditional models for funding drug development are faltering. In the US and many other developed countries, the average cost of bringing a new drug to market has skyrocketed, even as patents on some of the industry’s most profitable drugs have expired. Venture capital has pulled back from early-stage life-sciences companies, and big pharmaceutical companies have seen fewer drugs reach the market per dollar spent on research and development..."