Because of the well documented problems with the Ann Return/Trade statistic on the results page, I have been analyzing systems using the symbol equity line.I wondering if the backscanner results are overstated.

For instance, using a 50 week moving average system, using 2 rules where where you BUY at the close when the 50 week MA is below price, and SHORT at the close when the 50 week MA is above price, the system would enter a short on 12/28/07 on the SP500 at 1478.49 and buy on 7/17/09 at 940.38. The price change during this time was -36.4%, so the short should have registered a gain of + 36.4%. But looking at the symbol equity line for this system, results in a gain of + 62.7%. Small differences can occur if you are starting with a base of 100 on this exact date or if you are going further back in history, but in general, profitable short position seem to be over stated by about double.

Similarly, unprofitable shorts seem to be understated. The same system would have entered a short on 8/5/11 at 1199.38, and bought at 1285.09. The market rallied + 7.1% during this time frame, so the short position should have resulted in a loss of - 7.1%. But the symbol equity line declined only -4.9%, understating the loss on this short.

Longs seem to suffer the same problem. On 9/30/10 this system would have gone long at 1104.51, closing the trade out on 8/5/11 at 1199.38, which is a gain of + 8.6%. But the symbol equity line gained 12.8%.

Please help me out with where I am going wrong in setting up this trade correctly, or confirm that in fact there is a problem with the backscanner.

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