Pat Walsh, the foudning editor of MacAdam/Cage, has these stats about slush in his excellent book 78 Reasons Why Your Book May Never Get Published (and 14 Reasons it Just Might):
50%: Things tossed out becasue they don't publish that genre
40%: Tossed after 1-2 page read by interns, etc. becasue they are bad
10%: rejected after careful reads, becasue they aren't bad, just not good enough...EXCEPT FOR A HANDFUL
That handful receive requests for full manuscripts.
Of the full manuscripts they request, they publish 1%.
Many people say that if there were a good manuscript in the slushpile, it would shine out like a beacon.
Walsh disagrees. He says, "A good clam will not undo the ills of a plateful of bad ones." In other words, reading slush can be nauseating, and you may suffer from guilt by association.
Macmillan New Writing in the UK takes ALL of its submissions over the transom, and takes only full manuscripts--so although agents are free to submit, everything is read as if it is slush. My numbers are dated, but the last time I heard they had received about 8,000 manuscripts and published 23. One editor there said that perhaps twice that many were "publishable", so publishable manuscripts (after the usual editing, etc) would be something like 46 out of 8,000 in their experience...That would mean that 99.4% aren't even in the race.
