Here is a graph I made this morning while playing around with some of my hand history data. The graph represents the frequency that a hand wins as a function of it’s hand strength when the pot is heads up on the river. All hands have been linearized to a value in the range of [0,1].

The red line represents situations where the hero bet the river, while the blue line represents situations where the hero check or called the river.
All things being equal all three lines would overlap exactly. That is to say, if you held a hand with strength .3, and your opponent held a random hand, your hand would win 30% of the time. But in poker, all things are not equal. Players cannot fold if you do not bet, and players cannot bluff if you do.
Notice that the “active” plot clearly demonstrates the value of bluffing with your worst hands. It’s also more likely that our hand is good if we feel confident enough to bet the river. When we have a strong hand which isn’t a lock passive river play is usually an indicator that we’ve been faced with opponent aggression.
So, when should you bluff, and when should you value bet? From the graph, it looks like passive play out performs active play for hand value in the range of roughly [.35,.55]. In other words, for the game conditions in this game, we should be betting the river or bluffing with almost every hand. In practice, this may not be true, but it is good to see that “first approximation game theory” seems to be verified by observed data.