I just read an articled on Yahoo sports entitled "A bogus milestone for A-Rod as he nears No. 600," and thought I would do some quick investigation into A-Rod's numbers over the course of his career.  If you didn't read the article, a summary is that the writer thinks A-Rod's HR numbers shouldn't count because he is an admitted steroid user, and he also implies that A-Rod used steroids more than just while with the Rangers, so that is the focus of my post.
So, there are a bunch of numbers after the jump.
(NB: This is my first ever FanPost and I'm not entirely sure how to make it look cool or anything like that, so just bear with me.)

(Statistics courtesy Yahoo! Sports)

The above chart shows A-Rod's season numbers for Home Runs, walks, and at-bats, as well as the team for which he played.  The last two columns are the average number of home runs/at-bat and home runs/plate appearance (walks + at-bats), respectively.  If you take a look at the HR/AB, the highest percentage while he played for the Mariners is 8.4% in 1999, the sixth year he played for them, though the likely cause is that he had less at-bats (down nearly 200 from the year before).  In 2000, the percentage goes down slightly to 7.4%, though the at-bats increase by 50.  His average while playing for Seattle was slightly higher than 6%.

The numbers change drastically when A-Rod moves to Texas (the admitted steroid years).  Those are 3 of the 5 highest-production years in terms of home runs, with an average of 52 HR/year in that period.  His HR/AB also made a sharp increase during those 3 years, an increase of over 2% (6.0% at Seattle to 8.4% at Texas), and likewise his HR/PA increased just under 2% in that period (5.5% at Seattle to 7.4% at Texas).  Surprisingly, the highest-production year (HR-wise) in A-Rod's career-to-date was not his highest-production year in these two categories.  In 2002, A-Rod hit 57 home runs for Texas, beating out his next highest year by 3 home runs (2007 with the Yankees).  However, these numbers are balanced out by the disparity in at-bats and plate-appearances:

• 2002:  57 HR, 87 BB, 624 AB, 9.1% HR/AB, 8.02% HR/PA
• 2007:  54 HR, 95 BB, 586 AB, 9.3% HR/AB, 7.96% HR/PA

I'm not entirely sure what to make of this disparity between 2002 and 2007, except that 2002 was a huge year surrounded by other big years, while 2007 was a huge year sandwiched between a couple average years.

Anyways, A-Rod's production in New York has averaged 7% HR/AB and 6% HR/PA, which is substantially lower than the 8.4% and 7.4% respectively in Texas.  2005 and 2007 are both anomalies during A-Rod's time with the Yankees, as they are his only seasons with over 40 home runs and over 6.8% HR/AB and 6.1% HR/PA.  However, I don't think those 2 years are enough to say that OMG, ARDO'S BEEN JUICING IN NOO YORRRK!!!!1!!!!!one!!!!!!!  If anything, I would chalk that up to having a couple peak years in his early 30s, with an off-year in between.

As far as conclusions to be drawn from all of this, I am reserving judgment on the ethical issues involved in steroid use.  However, I will hazard a guess that Texas was the big anomaly in A-Rod's career, and he has not been using steroids since being traded to the Yankees.  Another interesting conclusion to be drawn from this is that (if I am reading this correctly) A-Rod I due to hit quite a few more home runs this season, since he has averaged 6.9% HR/AB in NY, while this year he has been down over 2%.  I don't know my way around the alphabet soup you guys call sabermetrics, but that makes me think he's been having some bad luck at the plate thus far in the season, so perhaps he will have some more good luck in the second half.

Any comments would be appreciated.