Risk register · entry
Q4 · Where models dieBlack Monday
Portfolio insurance fed on itself until the market fell a fifth in a day.
The world stops matching the model. Regime change and leverage turn a small error fatal.
Why this room
Portfolio insurance was sold as a simple, thin-tailed hedge but its mechanical, synchronized selling turned the payoff structure complex and manufactured a fat tail the model itself had assumed away, the textbook Q4 failure of elegant models meeting real-world correlation.
The record
- Dow Jones fell 508.32 points, 22.6 percent, closing at 1,738.74 down from 2,246.74 on October 19, 1987certain
- S&P 500 fell 20.47 percent on October 19, 1987certain
- Worldwide equity losses estimated at 1.71 trillion dollarslikely
- UK FTSE 100 fell 23 percent over two dayscertain
- Hong Kong market fell 45.8 percentcertain
- Federal Reserve injected 17 billion dollars into the banking system on October 20, 1987, over 25 percent of bank reserve balances and about 7 percent of the monetary basecertain
- 195 of 2,257 NYSE-listed stocks experienced trading delays or halts on October 19; 95 of the S&P 500 and 11 of the 30 Dow stocks opened latecertain
- S&P 500 did not regain its pre-crash high until July 26, 1989certain
- An estimated 60 to 90 billion dollars in institutional assets were run through portfolio insurance strategies by October 1987likely
- Portfolio insurance developed by Hayne Leland and Mark Rubinstein, commercialized via Leland O'Brien Rubinstein Associates (LOR), built on the Black-Scholes modelcertain
- Presidential Task Force on Market Mechanisms (Brady Commission) reported in January 1988likely
Sources
The book
This entry is one of 111 in the register. The full story, and what it cost the people who lived it, is in Risky Business by Claudia Zeisberger, David Munro and Joanna Reijgersberg-Siew.
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