Depends on where I'm hunting, how late in the season, layout of the body of water I'm on, wind velocity, local birds or new birds from the north and how hot my coffee is that morning. Over the years I've read some stuff that added to my knowledge as to how many to put out, but most of it has come from trail and error.
It's never more than a good guess, ya just gotta be willing to change your pitch when they ain't swingin. Whether huntin or fishin, being stubborn has probably cost me more opportunity than most other causes combined.
Sometimes, less is better.
