By Charlotte Beugge

While investors are constantly told that if you want to make money, you have to hang on for the long term, in the US the average shareholding lasts just 22 seconds - and that's a 10% increase from the 20-second typical holding time a year ago.

The tiny fractions of time shares are held for is down to computer-driven high frequency trading, according to a report in the Daily Telegraph.

Michael Hudson, a former Wall Street economist at Chase Manhattan Bank, told the newspaper: "Take any stock in the United States. The average time in which you hold a stock (has) … gone up from 20 seconds to 22 seconds in the last year.

"Most trades are computerised. Most trades are short-term…The financial sector is short term, yet they talk as if they're long term."

High frequency trading accounts for about 70% of all trades and is the subject of the Robert Harris bestseller, The Fear Index. However, for most investors hanging on to shares for the medium to long term is probably better.

Not only is it difficult to trade that quickly, even if you have an internet share-dealing account, but the costs - stockbroking and stamp duty at 0.5% - mean it is not worth it.

High frequency trading by funds involves huge bundles of stock so even tiny movements in share prices can make money for the fund managers.