blademan
You are asking a million dollar question my friend! Is that a trick question or it is a serious inquiry?
Never mind, I'm just teasing you. lol.
Now, there are several other online sources where that answer is readily available but you would have to do a bit of some goggle searching to come across that info.
Perhaps if you just put in google search engine "how often do doubles occur in the Pick3/4" you may come across the info.
Good luck in your search.