I think bluffing is a thing that ppl with limited experience of poker think the game is all about. It`s not!!!
Obviously there are different types of bluffs, but I think (accepting that in some low level buyins ppl will go all in with ziltch) the amount of time someone will try a stone cold bluff without any outs must be below 5% on average.
In general, as has been said, it will depend on chip stacks, outs, stage of tourny, read on players, etc.