On pahster's Sun Deck thread about the correlates of run-scoring: 1998 - 2006, he noted how GPA (Gross Production Average) correlates more strongly with runs scored than does any other of his stat columns.

According to pahster, the formula for GPA "is (1.8*OBP)+SLG/4. It is a more 'precise' form of OPS in that it weights OBP by an additional 80%. This is because previous studies have indicated that it is that much more valuable than is slugging."

Here is pahster's pertinent row showing that AVG correlates least of all the stats and GPA correlates the most with runs scored.

R AVG OBP SLG OPS ModOPS GPA

R 1 .812 .898 .890 .946 .917 .954

My question for pahster -- I'm not permitted to post on Sun Deck -- would be the following: Why doesn't GPA (.954) correlate with runs at a disproportionately higher rate compared to plain old OPS (.946)?

Why are GPA (where OBP has been weighted almost 2X SLG, coupled with SLG's being reduced again by being divided by 4) and OPS so similar to each other in their correlation to runs?

Isn't OPS virtually equal to GPA as a correlate to runs scored?