My numbers are a little better than that. I invited 27 people to review my latest book manuscript. One said no. Six never responded. Two said yes but I never heard from them again -- ever. Eleven provided very limited or minimally helpful input, three provided extremely valuable feedback, and the rest were somewhat helpful.

This was a larger review group than I usually enlist, but the percentage distribution is typical. I'm lucky if I have just 3 or 4 reviewers who do a really good job. I'm very grateful to those stalwarts!