Randy Johnson has announced his retirement. A sure-fire Hall of Famer, of course, but how good really was Johnson? Below the fold, I run some quick numbers. These are career stats - Johnson's prime from 1993-2002 stacks up even more impressively against the prime of any other lefthanded pitcher with a long career - and some of the calculations are a little rough, but you should get the idea: Johnson was probably the second-best lefthanded pitcher ever (behind Lefty Grove) and has a case for #1, depending how one weighs adjustments for different eras of the game.

Guide to the numbers below - ERA+, as regular readers know, is the park-adjusted league ERA divided by the pitcher's ERA, so it's a % of how far better than league-average a pitcher's ERA was. An ERA+ of 200 means an ERA half the league. The sample below compares Johnson to the other 28 lefthanded pitchers since 1871 to throw 3,000 or more career innings (so: no Koufax) with an ERA+ of 100 or better, of which Johnson's ERA+ of 136 places him second only to Lefty Grove.

QI or Quality Innings is ERA+ times IP - basically a quick method for combining quality and quantity.

LgERA is the park-adjusted baseline used to compute ERA+

BIP% is a rough calculation of balls in play that became hits, the part of the pitcher's game that depends upon defense (also luck, but luck evens out pretty well over this many innings).

For BB/9, I combined walks with hit batsmen (Johnson put a lot of guys on base that way).

dERA is a measurement of defense-independent ERA based on Voros McCracken's DIPS formula designed to compute what a defense-independent ERA should have been (based on a pitcher's HR, BB, K and HBP allowed, assuming an average defense), although given the uneven availability of intentional walk data I left out Voros' adjustments for IBB.

dERA+ is dERA divided by LgERA, to quickly adjust for differing playing conditions.

QdI is the Quality Innings formula again, except using dERA+

As you will see, when you rank the lefties all-time by QI, the race goes to the longest-distance runners (Spahn and Carlton), but ranked by QdI, Johnson - with his massive K numbers making him less dependent on his defense - pulls to #1.

Note also that by plain old wins and losses, Johnson clocks in at 137 games over .500, second only to Grove (+159), followed by Eddie Plank (+132), Whitey Ford (+130), Warren Spahn (+118) and Tom Glavine (+102).