When will the bear market in equities reach its bottom? And what will be the shape and magnitude of the recovery? History provides some clues.

There have been 16 bear markets since the Great Depression of the 1930s; periods during which shares fell by at least 20 per cent. While the trading patterns near each bottom are unique, they share important characteristics.

To forecast how painful a bear market is likely be, the best approach is to measure the size of the preceding bull run.

There have been six "weak" bull markets since the Great Depression, where prices rose by no more than by 60 per cent. Each bear market that followed was weak, with price drops of less than 27 per cent. On the other hand, nine of 10 more powerful bull markets were followed by declines of more than 27 per cent.

Using this rule, the current downturn should not be worse than 27 per cent below the peak.

But what will the shape of the final recovery look like? If you plot every bear market bottom, taking data over several months, three kinds of market bottoms are frequently encountered: plateaus, V-shapes, and slow-and-steady risers.

Plateaus are market low-points followed by flat or aimless price fluctuations, generally for four months or more.

There have been two post-bear market plateaus - in 1949 and 1990. Painful recessions were running both times. The stock market fell because of the economic slowdown and then hit a plateau until signs of recovery began to appear.

Such a pattern seems unlikely this time around, so long as Britain and other European economies can avoid recession.

The V-shaped variety features very sharp drops at the tail-end of a bear market, triggered by shocks to the financial system. The first month of the bull run that follows is equally exciting, with rallies of 12 per cent or more.

A recent example occurred in 1998, when investors took fright from three sudden shocks involving Asia, Russia and the collapse of a large hedge fund. Prices dropped 25 per cent in less than three months.

The recovery was equally exciting. Shares rose 17 per cent in one month and regained all the lost ground in just six months.

Slow-and-steady rallies are more leisurely affairs. The actual bottom is typically created over several weeks, usually featuring a test or revisit to the bottom and a more gradual rise.

If history is any guide, the bear market of 2000-2001 is likely to end with a rally of the slow-and-steady category.

David Schwartz is a stock market historian.