Asset price bubble

An asset price bubble is characterised by a surge in prices that raises expectations of further increases that generate a succession increases until confidence falters, the bubble "bursts", and prices rapidly revert to an objectively-based level. Asset price bubbles can cause extensive economic damage and can even threaten the integrity of the financial system.

The nature of asset price bubbles

A steep and sustained price rise and then its precipitous collapse, both unrelated to the asset's properties - that is the pattern of events which has characterised hundreds of episodes from the "South Sea Bubble" of the 17th century to the housing bubbles of the early 21st century. There is no objective way of assessing the truth of any of the various explanations that have been advanced for them. Their "information cascade" component has been observed in other contexts , and the "herding" behaviour that they exhibit has characterised the conduct of the subjects of many experimental studies of human behaviour. One surge in share prices has been termed "irrational exuberance", and that term has since been applied to other episodes, but whether the word "irrational" is really justified turns on the choice of interpretation. Such behaviour has been attributed to ill-informed noise traders, but John Maynard Keynes, himself a successful investor has attributed also to professional investors:

"professional investment may be likened to those newspaper competitions in which the competitors have to pick out the six prettiest faces from a hundred photographs, the prize being awarded to the competitor whose choice most nearly corresponds to the average preferences of the competitors as a whole; so that each competitor has to pick, not those faces which he himself finds prettiest, but those which he thinks likeliest to catch the fancy of the other competitors, all of whom are looking at the problem from the same point of view."

The use of stop-loss orders that probably contributes to the speed of decline when a stock exchange bubble bursts, and is itself a form of herding behaviour, is widely practised by professional investors .