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Global stock markets, and the US markets in particular, have displayed a large
degree of volatility since the middle of last year and daily fluctuations are
now back at levels last seen in 2003. This is shown clearly by the following
graph of the daily change in the value of the S&P 500 Index.

Source: StockCharts.com
In the nature of stock markets, some investors seem ready to turn tail at
the first sign of bad news. On the other hand, there are those who are only
interested in knowing whether the current bear phase has bottomed so that they
can buy stocks again.
This begs the question: When is the right time to buy stocks? Unfortunately
there is no straightforward answer, irrespective of the amount of analysis
thrown at the issue. But let's step aside from trying to time the market by
simply considering what the chances would be of losing/making money on the
stock market over different holding periods.
I have asked the research team of my investment firm, Plexus Asset Management,
to conduct an analysis of the returns of the S&P 500 Index for different
holding periods over the past 51 years (i.e. from the inception of the "new-look" S&P
500 Index in 1957 through 2008). Both price movements and dividends were included
in the return calculations.
The following graph and table summarize the research results:


The analysis of the one-month holding periods indicated that 36.3% of all
the periods resulted in a negative return and that 63.7% of all the periods
therefore recorded a positive return. The best one-month period (September
1982) showed a return of 12.1% and the worst month (October 1987) a return
of -21.6%, while the average monthly return was 0.9%.
It therefore seems as if the likelihood of a profit over the one-month period
is better than the likelihood of a loss, but in view of a probability of 36%
investors will still have a tough time knowing how the situation will play
itself out.
Unless you have the proverbial crystal ball, why take the risk of investing
in the stock market? It is for the simple reason that the situation looks significantly
different over longer periods – the longer the investment term, the less
chance of ending up in the red.
By increasing the investment term to one year, the picture already starts
improving. 76.9% of all the one-year periods showed a positive return, i.e.
23.1% of these periods registered negative returns. Furthermore, the best one-year
period (August 1982 to July 1983) showed a return of 60.2% and the worst (November
1973 to October 1974) a return of -34.2%. The average return was 11.9%.
As can be expected, investors fared much better over the five-year holding
periods. A loss was made in only 8.0% of the periods, while the average return
amounted to 10.8% per annum. The best period (September 1982 to August 1987)
showed a return of 29.7% per annum, whereas the worst period (April 1998 to
March 2003) recorded a return of -3.8% per annum.
Stretching the holding period even longer, not a single one of the 493 rolling
ten-year periods produced a negative return. The average return for staying
invested for ten years was 11.1% per annum.
The research results are not offered as an alternative to sound fundamental
and technical models (or perhaps an experienced "gut") with a track record
of having accurately identified entry or exit levels over time. It merely serves
the purpose of alerting investors to the stock market's return profile over
different holding periods in order to (1) know what they are "up against",
and (2) properly match their investment personalities with investment periods
that are optimal for allowing them a good night's sleep en route to an improved
lifestyle.
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