I will probably regret this, but I have to know. If it's only semi-baseless, what is the piece of the base that points to something as specific as 200 innings, 3.80 ERA? And why are you not considering defense, line-up placement or baserunning? Normally, your posts are supported to a degree bordering on the absurd, so this just seems out of character, and frankly, totally pulled out of your ass. (Not that pulling declarative statements out of one's ass is a bad thing - I fully rely on it.)
I figure there's more to it than that, so crack out the pre tags, and let's trudge through this shit properly.
I mean semi-baseless in that it's based on some formulaic assumptions that have their deficiencies and that many people who read these boards find totally baseless. It's a caveat.
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If you want to know the exact methodology, it was this:
1) For the offensive part, compare Burke's estimated runs created to Iguchi's estimated runs created based on their career totals, given 650 at-bats. That's where the speculated offensive difference of 15 to 20 extra runs comes from:
Burke: .319 career OBP * .377 career slugging * 650 at-bats = 78 runs created
Iguchi: .347 career OBP * .421 career slugging * 650 at-bats = 95 runs created
I figure the estimated 17-run difference can be called 15 to 20.
2) For the pitching part, figure out what it would take for a starting pitcher throwing 200 innings to shave 20 runs off the Astros' team runs allowed from last season:
2007 Astros = 813 runs in 1464.7 innings pitched (5.00 runs per 9 innings pitched)
A pitcher throwing 200 innings at that rate would give up 111 runs.
The hypothetical No. 2 would throw 200 innings but give up 20 fewer runs, i.e., 91 runs (4.10 runs per 9 innings pitched).
Now, convert runs allowed into earned runs allowed. Last year the Astros 0.94 earned runs for every run allowed. Using that same ratio for the hypothetical No. 2, that's 91 runs times 0.94, or 85 earned runs allowed in 200 innings pitched. That's a 3.83 ERA.
I figure the 3.83 ERA can be called 3.80.
So, the assumptions are, just to cite a few, whether (1) you think there is any merit to runs created estimates (OBP * slugging * at-bats), which tend to work with about a 5% margin of error at the team and league level, (2) whether you think 650 at-bats is a reasonable estimate for the amount of playing time Burke vs. Iguchi would get, (3) whether Iguchi and Burke would continue to produce at their career levels or something close, (4) whether you think a No. 2 starter would throw roughly 200 innings pitched, (5) whether the relationship of runs to earned runs holds and (6) whether you think Iguchi creating an estimated 20 more runs than Burke as the regular second baseman is roughly equivalent to a No. 2 starter allowing 20 fewer runs than what the Astros put on the mound in 2007.
I'm not saying it's totally made up, but it's not gospel either. It's an educated guess of what impact players with those numbers might have on a team. I didn't consider the other stuff because this could be done on the back of an envelope. The other stuff would take a lot more work. Plus, since I think these kinds of calculations are really just ballpark figures (no pun intended) anyway, throwing more stuff into the mix doesn't really make it more precise. It just adds to the weight of stuff already built upon the somewhat precarious assumptions.
