it varies so much between region and time of year. on the coast it may be one out of a dozen sets (random sets without cherry picking those areas you come across with tons of fresh sign)
over east it's much, much better. I went over to my bro in law's house (east of Burns,Or) and we made 11 sets in 2 days, and called in coyotes 9 of those sets.... a couple sets we called in 2. if that was averaged out, it would have been over one dog per set.
i think a fair avg over east would be one dog every 3 sets called in if conditions were ok.... there are places over there that are hunted harder that's much tougher hunting.
we aren't getting every one we call in killed either, probably just over half.... get one called in on the coast and it's usually dead, but setups are so much more important to just verify you called one in.
I think over here, I call in more than I know about, but they never come into the open, and get my wind before they are seen.