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Portfolio123 » List all forums » Forum: Screener » Thread: Screener back testing question long vs short |
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Total posts in this thread: 4 |
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quester
Member
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Could someone help me to understand how screener back testing evaluates long transactions and short transactions. My query comes from simple test of (what I think is a short screen). When I evaluate it using type of transaction: short, it shows a loss. When I evaluate it with type of transaction: long, it shows (a bigger) loss. Not sure how this can be... I guess I do not understand how these calculations are made. Any help would be appreciated. |
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marco
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Please indicate which screen and the settings you are using for each scenario. Thank you ---------------------------------------- Portfolio123 Staff |
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czfan11
Member
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yea, it is seems true for any sreenbacktest, the difference is not quite understandable. |
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quester
Member
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I think I figured it out by trial and error and seeing some other posts on the forum. Seems P123 within its limits is doing things correctly. Seen discussion about dividends, etc not being included yet...I understand. The big source of my apparent strange result is when inputing commissions and slippage. If you do long transactions (to see if a short idea properly loses money) both slippage and commissions make you lose more ( so you think higher profit) than you would if you had actually gone short (commissions are always a loss). Other posts point out in that case you need to input negative slippage and negative commissions. I set up this screen to help me understand exactly what was going on http://www.portfolio123.com/app/screen/summary/36239?st=1 It's just a screen that opens a position on ticker SH (an S&P500 short ETF) If you change transaction type to short vs long you can see performance flip. if you add slippage and or commissions you and change between long and short you can see the effect. Now I am comfortable the performance matches how it should be calculated (dividends still not included either long or short, I guess) I'm still learning the P123 system. Hope I don't bother you all too much. |
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