Ed Bain's 4 + 30 Percentages & Profitability Book (Published in 2001)
This is a Downloadable PDF Copy of this book.

Ed explains how he derived and came to bet his 4 + 30 signature stat which means this trainer has produced 4 wins or more plus a 30% win rate on a specific trainer move.  The book predominantly covers how he used this to bet trainers bringing horses off a Layoff or how they perform after a Claim.