Winning %'s on the Showdown

I was just wondering if there is a certain winning percentage "winning players" have on the river, WHEN THEY HAVE TO SHOWDOWN AGAINST AN OPPONENT. this would be for limit HE games, and if there is a certain %, you strive for on showdowns, what is it? or does this even matter? and does they type of game you play in(tight/loose) have a major effect on those %'s.

thanks!