Detecting financial bubbles in real-time

From the current issue of The Economist comes this report comparing the Chinese stock market with other famous bubbles - it doesn't look so bad. It's a wonder how former Fed Chairman Alan Greenspan can be so confident in his first "real-time" detection of a financial bubble.

ALAN GREENSPAN, the former chairman of America's Federal Reserve, always insisted when in office that it was extremely hard to spot bubbles before they had actually burst. This, he said, is one reason why policymakers should never try to prick them. Today, however, he seems to have no doubts that China's stockmarket is bubbling over. He recently declared that Chinese share prices were “clearly unsustainable”, with a risk of a “dramatic contraction”.

It is curious that China's bubble seems so blindingly obvious to Mr Greenspan and so many other Americans who remained in denial about their own dotcom mania right to the end. For according to The Economist's “Bubble guide” (see chart), China's recent share-price boom is still relatively modest compared with the giants of history. The chart plots the performance of Chinese share prices over the past five years against the three great bubbles of the 20th century: Wall Street in the 1920s, Japan in the 1980s and America's NASDAQ in the 1990s. The NASDAQ composite index saw a gain of more than 500% from 1995 to early 2000. Japan's Nikkei 225 jumped by 300% from 1984 to 1989. The Shanghai A-share index, having recovered most of its plunge in late May, shows a gain of about only 160% over the past five years.

Moreover, Chinese A-shares now have an average price-earnings (p/e) ratio of around 45. At their peaks, the average p/e ratio of the Nikkei 225 in 1989 and the NASDAQ at the start of 2000 were both well over 100. This suggests that Chinese share prices could have much further to climb before the bubble bursts—unless China's policymakers are braver than Mr Greenspan and take bolder action to dampen the market now.

Maybe the bubble declaration was a result of the media tiring of his monthly U.S. recession probability update/clarification and he thought it was time move on to a new topic.