This is not a study. I am not proving anything. This is an illustration, meant to showcase just how meaningless this stuff is. (There isn't a robust database of spring training results, as there is for the regular season, so the data set is limited to well below a meaningful sample size by my limited ambition to talk about this topic. So all of the figures and conclusions below are to be taken with a grain of salt; they simply illustrate the concept. They're examples.)
I took the spring training ERA and FIP-ERA from everyone who pitched in Cubs camp last year, and took a look at the weighted average error of those ERAs compared to what those pitchers did in the regular season.
So, a 4.00 ERA in spring training could mean a guy is a 2.26 ERA pitcher, or a 5.74 ERA pitcher. That's pretty much the difference between being the Cy Young winner and being designated for assignment. It's so absurdly large as to be absolutely meaningless.
So when you read things like this:
Jon Lieber's four shutout innings Saturday against Arizona put him in good position for the Cubs' fifth starter's spot.
But Ryan Dempster and Jason Marquis also have pitched well, making it a tough call for manager Lou Piniella.
"That's what competition for spots does," Piniella said.
Take it with a pinch of salt. Do not hyper ventilate or overanalyze. It's all meaningless; Lieber's four shutout innings are an utterly meaningless indicator of his future performance. Now, they way he pitched those innings could indicate his future performance; I have no worries that the Cubs have scouts who have at least some ability to divine difference in performance that ERA can't capture at this point.
But we armchair analysts know pretty much nothing more than what we knew yesterday, which is basically what we knew the day before.
I will continue to state this come April. In fact, excluding learning new ways of looking at the data I already have (and I won't pretend that's not a possibility), the absolute earliest I will know something new about the abilities of any individual ballplayer is probably May. Maybe June. Just so's everyone's aware.