Was the Chinese share market crash rational asset-price movements without news?

Large share market crashes  such as over the recent months in China and the 1987 Wall Street crash do not necessarily imply an economic slowdown.

The majority of major share market movements occur without any particular news hitting the market. Studies of the 50 largest share market movements in the US stock market between 1946 and 1987 found that the majority of them could not be explained by news. That includes the 1987 share market crash. In October 1987, shares fell by 20% in one day for no obvious reason.

David Romer explained these booms and busts, including the 1987 share market crash in two ways: investor uncertainty about the quality of other investors’ information; and dispersion of information and small costs to trading:

Asset prices can change because initially the market does an imperfect job of revealing the relevant information possessed by different investors and because developments within the market can then somehow cause more of that information to be revealed…

The possibility of imperfect aggregation implies an alternative to external news and irrationality as a potential source of asset-price movements: some price changes may be caused by “internal” news.

That is, asset prices can change because initially the market does an imperfect job of revealing the relevant information possessed by different investors and because developments within the market can then somehow cause more of that information to be revealed.

Either of these models are perfectly plausible. Investors learn from each other through trading and improve their estimations of the value of various shares.

As such, through internal learning and discovery within the share market there can be booms and crashes despite no new information, no communication, and no coordination among the participants in trading. Underneath the surface, there is a gradual updating of information by the participants and at a certain point in time, this causes a sudden change of behaviour.

Dow and Gorton made similar points to David Romer about how share market learning is a process of learning, judgement and error correction rather than an instant adjustment:

Strategic interaction and the complexity of the information result in a protracted price response.

Indeed, equilibrium price paths of the model may display reversals in which the two traders rationally revise their beliefs, first in one direction, and then in the opposite direction, even though no new information has entered the system.

A piece of information which is initially thought to be bad news may be revealed, through trading, to be good news.

Bubbles and crashes are consistent with private information held by a few slowly dispersing among market participants until this knowledge was reflected in stock prices as in Hayek’s (1945) analysis of the price mechanism as a means of communicating information.

HT: The one thing you should remember about the stock market crash of 1987 | Business Insider.

The share market speaks on recent British elections

The share market speaks on Grexit: banknote printer shares soar

The share market speaks on renewable energy

The share market as a spy, investigator and muckraker: using share price movements to uncover secrets and solve mysteries

Armen Alchian successfully identifying lithium as the fissile fuel in the Bikini Atoll atomic bomb using only publicly available financial data. The early 1954 RAND corporation memo by Alchian was classified a few days later.

The Stock Market Speaks: How Dr. Alchian Learned to Build the Bomb by Joseph Michael Newhard, August 27, 2013 at for a replication study of Alchian’s event study of share market reactions to the Bikini Atoll nuclear detonations in 1954 updated with declassified information and modern finance theory.

An extra challenge for Alchian was not only was the component of the bomb classified, whether the explosion was atomic or hydrogen was classified too.

The share price of the supplier of lithium surged within a few days.

The replication study by Newhard found a significant upward movement in the price of Lithium Corporation relative to the other corporations. Within three weeks of the explosion, its shares were up 48% before settling down to a monthly return of 28% despite secrecy, scientific uncertainty, and public confusion surrounding the test; the company saw a return of 461% for the year.

The share market is a surprising efficient tool for discerning new knowledge.

After the Challenger space shuttle disaster in 1986, the share market identified within the hour which component supplier made the faulty part and marked it down accurately as to damages and loss of business. The blue ribbon commission of inquiry took 6-months to find the culprit.

In the period immediately following the crash, securities trading in the four main shuttle contractors singled out Morton Thiokol as having manufactured the faulty component.

Intraday stock price movements following the challenger disaster


At market close, Thiokol’s shares were down nearly 12 per cent. By contrast, the share prices of the three other firms started to creep back up, and by the end of the day their value had fallen only around 3 per cent.

Morton Thiokol shed some $200 million in market value on the day. Over the next several months, the other contractors recovered and outperformed the market while Morton Thiokol lagged.

As a result of the investigation, Morton Thiokol had to pay legal settlements and perform repair work of $409 million at no profit. It also dropped out of bidding for future business.

The $200 million equity decline for Morton Thiokol in hindsight is a reasonable prediction of lost cash flows that came as a result of the judgment of culpability in the crash.

William Brown found that a group of firms that had significant ties to Lyndon Johnson increased in the market value after President Kennedy’s assassination. The share prices of General Dynamics, whose main aircraft plant was located in Fort Worth, Texas, climbed from $23.75 on November 22 to $25.13 on November 26, and by February 1964 was up over $30, a jump of around 30 per cent in three months.

Over the ten trading days following the announcement of Timothy Geithner’s nomination as U.S. Treasury Secretary, financial firms with a connection to Geithner experienced a cumulative abnormal return of about 12% relative to other financial sector firms. This reversed when his nomination ran into trouble due to unexpected tax return issues.

Pat Akey (2013) looked at the abnormal returns in share prices around close U.S. congressional elections. Firms gain on the election of a politician with whom they are connected – and they lost when he or she is defeated. The cumulative abnormal return to be between 1.7% and 6%.


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