What Contribution Can Behavioural Finance Make to the Explanation of Stock Market Bubbles and Crashes?

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The occurrence of stock market bubbles and crashes is often cited as evidence against the efficient market hypothesis. It is argued that new information is rarely, if ever, capable of explaining the sudden and dramatic share price movements observed during bubbles and crashes. Samuelson (1998) distinguished between micro efficiency and macro efficiency. Samuelson took the view that major stock markets are micro efficient in the sense that stocks are (nearly) correctly priced relative to each other, whereas the stock markets are macro inefficient. Macro inefficiency means that prices, at the aggregate level, can deviate from fair values over time. Jung and Shiller (2002) concurred with Samuelson’s view and suggested that waves of over- and undervaluation occur for the aggregate market over time. Stock markets are seen as having some predictability in the aggregate and over the long run.

CHARACTERISTICS OF BUBBLES AND CRASHES

Bubbles and crashes have a history that goes back at least to the seventeenth century (MacKay 1852). Some writers have suggested that bubbles show common characteristics. Band (1989) said that market tops exhibited the following features: 1. Prices have risen dramatically.

2. Widespread rejection of the conventional methods of share valuation, and the emergence of new ‘theories’ to explain why share prices should be much higher than the conventional methods would indicate. 3. Proliferation of investment schemes offering very high returns very quickly. 4. Intense, and temporarily successful, speculation by uninformed investors. 5. Popular enthusiasm for leveraged (geared) investments.

6. Selling by corporate insiders, and other long-term investors. 7. Extremely high trading volume in shares.
Kindleberger (1989) and Kindleberger and Aliber (2005) argued that most bubbles and crashes have common characteristics. Bubbles feature large and rapid price increases, which result in share prices rising to unrealistically high levels. Bubbles typically begin with a justifiable rise in stock prices.The justification may be a technological advance, or a general rise in prosperity. Examples of technological advance stimulating share price rises might include the development of the automobile and radio in the 1920s and the emergence of the Internet in the late 1990s. Examples of increasing prosperity leading to price rises could be the United States,Western Europe, and Japan in the 1980s. Cassidy (2002) suggested that this initial stage is characterised by a new idea or product causing changes in expectations about the future. Early investors in companies involved with the innovation make very high returns, which attract the attention of others. The rise in share prices, if substantial and prolonged, leads to members of the public believing that prices will continue to rise. People who do not normally invest begin to buy shares in the belief that prices will continue to rise. More and more people, typically people who have no knowledge of financial markets, buy shares. This pushes up prices even further. There is euphoria and manic buying. This causes further price rises. There is a self-fulfilling prophecy wherein the belief that prices will rise brings about the rise, since it leads to buying. People with no knowledge of investment often believe that if share prices have risen recently, those prices will continue to rise in the future. Cassidy (2002) divides this process into a boom stage and a euphoria stage. In the boom stage share price rises generate media interest, which spreads the excitement across a wider audience. Even the professionals working for institutional investors become involved. In the euphoria stage investment principles, and even common sense, are discarded. Conventional wisdom is rejected in favour of the view that it is ‘all different this time’. Prices lose touch with reality. One assumption of the efficient market hypothesis is that investors are rational. This does not require...
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