You lose 3 LP for your first dodge of the day (5 minute time out), and 10 LP (30 minute time out) for every dodge there after.
Depending on the skill difference of the game, you can lose anywhere from 3 to (from what I've seen) 15 LP.
So if the other team is a very easy win skill difference wise, you are better off dodging (though...why would you?). If they are tougher or roughly equal skilled, you will lose more LP dodging than losing.
You can't tell skill difference until you get in-game is the thing though.