I'm not familiar with this book in any way, so I'm curious, what is that 20% statistic based on?
20% on any random hole? 20% of the time a player who shoots 80 will have less putts in an entire round than a pro? Does this take into account GIR (I.e. Do both the pro and the amateur have the same GIR%)?
To me, statistics don't always mean much without understanding what they're based on. So I'm not trying be a pain, but would like to understand what that 20% truly represents.
I said out-putt. I didn't say "take fewer putts than" or anything else. I said "out-putt." So… no, it's not based on any of the methods you mentioned as such a stat would be virtually meaningless. Someone who misses 18 GIR is almost bound to have fewer putts than a guy who hits all 18.
Clue: It's on page 56 according to my notes, right inside the "Strokes Gained Putting" chapter. More blatant clue: He's talking simply about strokes gained, which is one of the fairest measures of putting performance. A 90s golfer out-putts a PGA Tour pro 10% of the time, and a scratch golfer about 30% of the time.
It's off topic for this thread AND contains material in both his book and my own, so I encourage you to buy both. Simply put: PGA Tour pros are not phenomenally awesome putters. That's not why they're on the PGA Tour, and that's not a skill they do so much better than even a guy who shoots in the 90s.