Go Long Term

The chief investment strategist at Merrill Lynch, Richard Bernstein, released a study this past summer. He found, in summary, that the longer you hold most asset classes, the more you reduce the chance of investment loss.
For example, with the S&P 500 index for the period from 1985 to mid-2006, if you bought the index and held for one day, the risk of loss was 46% due to market movements:
1 week-42%,
1 month-35%,
1 quarter-27%,
1 year-18%,
3 years-14% and
5 years-17%.