I've had a fairly specific concern about UZR/150 for a little while, and think this is as good a place as any to bring it.  I know there has been some heated discussion about the metric's ability to accurately measure individual value.  My question/concern has more to do with the metric at a team level.  I'm hoping people can look at my concern and let me know their thoughts.  Is my interpretation right?  Are my methods of measuring reasonable?  I'm not a statistical expert, so I'll have pretty thick skin about it.  I'm posting this more to learn myself than to educate anyone else.  

Anyway, my general view of UZR/150 is that it is a step in a positive direction but still a long ways from what we have when we quantify offense and pitching.  I accept that you need a very large sample to measure at an individual level.  At a team level, I would think that you could be able to interpret data sooner.  More specifically, I wanted to look at how the difference between a teams FIP and ERA correlates with the teams UZR/150.  Presumably, all other things being equal, a team that plays good defense will have an ERA that is better than their FIP and those that play poor defense will have an ERA worse than FIP.  With over half the season behind us, I expected to see a pretty tight correlation between where a team ranked in UZR/150 and where they rank in differential between ERA and FIP.  I'd say there is a correlation, but I was surprised to see how weak it is. 

***The standard deviation is based off the difference using absolute difference rather than tracking both negative and positive variances.  I think that is the "right way" to do it, but not sure.  I think the key really is to make sure you keep comparisons between standard deviations apples to apples, so that's what I'll do here.  I'll compare the variability with other measurements using absolute difference.***

I then wondered if I really need to be looking at the connection between UZR/150 and a pitching staff's BABIP.   This link is even a little bit weaker, with an average difference at 6.87 and a standard deviation at 4.58.

I would not be considered a great advocate of UZR, but even so, these connections are much looser than I expected them to be.  Translating it into offensive terms, these items have about the same connection that batting average has to a team's ability to score runs (Average difference 6.47, standard deviation - 3.80).  For another point of reference, Woba ties much closer to ability to score runs (at avg difference of 2.2 and standard deviation of 1.88).

Most surprising, though, was how much tighter the measurements of luck (LOB %, BABIP) tied to ERA minus FIP.  The luck factors correlate about  twice as strongly as the defense behind the pitching (as measured by UZR/150).  LOB % has an average difference of 3.33, with a standard deviation of 2.75.  BABIP has a 2.73 average difference and a 2.24 standard deviation.

This really wasn't what I expected to see.  I've sat on this for a couple weeks, deciding whether to bring it here.  I'm hoping it will either draw some good discussion, or point me to factors that I should (or shouldn't) be looking at.   Maybe they are obvious to all but me....I've just started trying to substantiate my general position on the metric.   Maybe this is as much a conversation on FIP as it is UZR.  Not sure.  I just found this all interesting and a little surprising.  We probably have the resources here to make sense of what I am unable to, and wanted to give it a shot.