I've been reading Slansky's Theory of Poker, and I've come across a problem with expressed odds...

Every poker site and book I've come across always counts possible outs as if none of those outs can be in the other player's hole cards; folded or active.

I figure that this is neither zero nor trivial, so I was wondering if anyone has done a probability analysis of the number of outs to subtract by number of players on the table, based on the average probability of someone holding a blocking card to a flush or straight.