Steroids and its role in ERA

Was talking to someone today and were discussing how ERA's have been down the last couple of years. My friend mentioned steroids, but my gut feeling was that much of the change has little to do with steroids usage (presumably) decreasing and more to do with the fact that many of the best hitters have aged or retired and there has been an unusually good crop of young pitchers. (Basically saying that it is largely cyclical, and we happen to be going through a time with unusually good young pitching.)

One possible way to analyze this would be to consider the ERA's of pitchers who pitched in both eras and see whether they have changed much. While it is not a perfect indicator, it may be a telling stat. If we see that regardless of age, pitchers (as a whole) who pitched in the steroid era all have lower ERA's following the end of the steroid era, it may lend a bit more credence to the idea that having the hitters on steroids made a big difference. If this is not really the case (and the drop in overall ERA is mostly focused amongst the young pitchers who were not yet pitching then (think Lincecum, Kershaw, King Felix etc.) it could just be that the quality of pitcher has decreased.

Anectdotally, it is interesting that some of the absolute best pitchers of all-time (Maddux, Clemens, Randy Johnson, Pedro) all pitched in the steroid era, and actually it seems like there were far more legendary pitchers in the 90's-ealy 00's than in eras like the 80's which were on a whole more pitchers eras.

Anyone know if anyone has done this kind of analysis? My gut is that most of the changes are amongst the new, younger crop, and players who have been around for 10 years or so as a whole are roughly the same (when considering all of them together) as they were back then. Of course I know variables like age make a big difference, but I am assuming (for simplicity sake) that this evens out for the most part.)

Note that another factor not really considered (that would not be shown such a study) is whether the quality of hitter decreased with the retiring of so many great hitters. (As weaker hitting could give the illusion that steroids played a role where they may not have.)

Thoughts?

Right now there is alot of good pitching and an abundance of mediocre hitters in the majors.. the ERA's reflect this trend.

I also think ERA are down because of some of the new ballparks in the last 5 years. For the most part they have been pitchers ballparks

I totally agree with the new pitcher friendly ballparks. Also, you cannot diminish the development of the cut fastball. Also, maybe the pitchers have caught up to the hitters chemically. Steroids are better suited for pitchers, recovery and explosiveness especially.