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6 votes
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Cem Kaner
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2 votesCem Kaner
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2 votesCem Kaner
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2 votesCem Kaner
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2 votesCem Kaner
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3 votesCem Kaner
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2 votes
An error occurred while saving the comment Cem Kaner
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I've been walking through the actual purchases in my backtests. My search requires stocks with Rec = Buy, but I am buying stocks that were buy yesterday but have dropped in price and are now Rec = Hold. This should not be happening.
Cem Kaner
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2 votesCem Kaner
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4 votesCem Kaner
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3 votesCem Kaner
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3 votesCem Kaner
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3 votesCem Kaner
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4 votesCem Kaner
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5 votesCem Kaner
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6 votesCem Kaner
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7 votesCem Kaner
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17 votesCem Kaner
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42 votesCem Kaner
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54 votesCem Kaner
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49 votesCem Kaner
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I initially dismissed this because I thought the impact would be relatively minor for the research I was doing. For example, I was comparing different VectorVest stopping rules and I expected the impact to be similar across the different conditions (so I could ignore it). However, all of my backtests produced results that were strikingly better than I expected. I was a stock market genius! So I tried some simple backtests that I could check elsewhere and the results came out so much better from VectorVest's backtester than what I think were the actual real-market results that I have no idea whether the impact of its bugs (e.g. survivorship bias) interacts differently with some conditions (e.g. different stopping rules) than with others.
As a result, I no longer use the backtester for anything. I can't figure out how to determine, in a compare-this-versus-that student whether the differences in results come from the differences between my test conditions or from a stronger effect of the bugs on some conditions than others. I can't find a way to trust the data enough for it to be useful.