Historical data will never be able to truly simulate manipulation or sympathetic, symbiotic or parasitic relationships. Ever back-test a trading system that simulates a Market Maker letting low block go under the bid or dialing down the sensitivity of the bid vs. the ask? Speaking from experience.
That's why I'm developing an algorithmic trading system based on sympathetic, symbiotic and parasitic hidden connections.
Also Ref: Contagious Speculation and a Cure for Cancer: A Non-Event that Made Stock Prices Soar - http://www0.gsb.columbia.edu/whoswho/getpub.cfm?pub=1555