In my opinion backtesting can be a very powerful tool if used correctly.
The problem is that many traders over-use the functions provided by the different backtesting software packages and think more is better. Many so-called system developers try to imply that the longer you backtest the better and more robust your system will be. That’s not always true.
Let me use the e-mini S&P as an example. In 2000 the average daily range was 100-150 ticks per day; in 2004 it was only 40-60 ticks per day. If you backtest any trend-following daytrading system in the e-mini S&P you will see that it worked perfectly until 2002 and then suddenly fell apart. It seems that there are no more intraday trends. That’s not surprising as the daily range of the e-mini S&P decreased by more than 50%.
What happened?
There are a couple of reasons. Probably the most important one is the introduction of the Pattern Day Trading Rule in August and September 2001by the NYSE and NASD: If a trader executes four or more day trades within a five business day period then he must maintain a minimum equity of $25,000 in his margin account at all times. Because of...