There's been tests done comparing prostate growth in rats to contractile tissue growth but it's arguably how accurate or scientific it is. I believe most ratios are estimates. In other words, if it takes about 9 times more primobolin to cause the androgenic side effects of test (which a mentioned is 1:1 and considered pure androgen, which in itself is arguable) then that would make the anabolic /androgenc raio of Primbolin 9:1 Anavar is about the same. I've seen it listed as high as 13:1 Dianabol is 3:1 Anadrol 2:1 Don't remember the others off hand.
I'd be hard pressed to prove the precise accuracy of these numbers but the estimate works well in determining the approximate anabolic/androgen ratio -- which is almost a non issue in many peoples stacks anyway.