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URL:  http://boards.fool.com/the-fundamental-problem-as-i-see-it-is-that-back-30689865.aspx

Subject:  Re: maybe done Date:  5/17/2013  7:44 PM
Author:  mark19601962 Number:  243146 of 251797

The fundamental problem as I see it is that back testing a screen tells you how that screen worked in a world that no longer exists and will probably never exist again. Unless that screen performed well due to fundamental principals that continue to exist into the future, there's no reason to think that a screen that did well in the past will do well in the future also.





Phil,

That is absolutely true, but what if a screen does well post discovery, and out of sample.

Also, there do seem to be some basic principles that we know are indicative of stock price. Value and momentum.

All that being said, sadly I have to agree with you, that the market keeps changing, so what worked before, may not work going forward.
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