What Caused the “Steroid” Era?

With Mark McGwire’s recent admission that he used steroids throughout the 1990s, there has been a resurgence of chatter regarding how to view the performances of the past 15–20 years. But, I think it’s wrong to attribute most of the high home run rates of this time-frame to steroid use. The connection that many people want to make is understandable. We have evidence that many players were using steroids during this era, and steroids have been shown to increase strength and power; therefore, it should follow that home run rates should rise accordingly. (And let me make this clear before I move to the next step: I believe wholeheartedly that steroids are effective ergogenic aids to baseball players—it’s growth hormone that does nothing.) However, I do not think steroids are the main cause of the dramatic rise in offense (particularly the home run) in the 1990s–2000s.

Why do I think this? Take a look at the following graphs. The first maps home runs per game from 1921 — 2009.


It’s clear that the present era is different from the past, but I also think it’s interesting how quickly it changed and did not change. In 1993, home runs per game jumped by 23%, and in 1994 they jumped 16%. Since that time, the average absolute change in home run rates has averaged about 5% and maxed out at 9%. Home run rates rose, then plateaued. The graph below zeros in on home runs per game since the 1990s.

HR/G 90s

If steroids were the cause of the steroid era, then we should have gradually seen them enter the game. A few players use and then others slowly adopt their technique. But that’s not what we observe. Almost overnight, home runs jumped. If you want to believe home runs are largely responsible for the change then you have to believe that players all got together in 1992 and 1993 and said, “hey, it’s juice time.”

But even more convincing in my mind is the fact that the home runs haven’t gone away with steroid testing. In 2005 (marked by a vertical line on each graph), Major League Baseball began drug testing with suspensions, and the home runs didn’t go away. You might be able to look at the graphs and identify a slight decline—it’s difficult to separate the noise from real changes with so few observations—but it’s clear that home runs aren’t close to their pre-1993 level. Yes, tests are imperfect and can be beaten, but the dramatic change in enforcement—from no monitoring or punishment to strict monitoring with punishment—ought to yield more substantial declines. Do I think steroid testing has taken away some power from its users? Absolutely, and it barely shows up in the aggregate data. In my mind, the rise must be attributable to something else. And if you think Ken Griffey had two seasons of 56 home runs without the help of steroids, then it would be useful to have an alternate theory.

So, if steroids aren’t the cause, then what is? I have a few theories.

1. MLB changed the ball. I have little doubt that the league allowed (or introduced) a lively ball into the league. This would have the effect of boosting home runs for all players. Certainly, I can’t prove this, but there have been whispers about it for years. This theory explains the dramatic rise in home runs and the lack of decline after testing.

2. Expansion. Baseball expanded by two teams in 1993 and two more in 1998. As I have detailed before (see here and here), as talent became diluted, excellent performances began to happen as the very best (hitters and pitchers) were able to take advantage of the very worst. The abrupt change in home runs fits exactly with the timing of expansion. Joe Posnanski also discussed the the possible influence of expansion (as well as a few other explanations) in a recent column.

3. New stadiums. Smaller parks and home-run alleys may have caused more home runs to fly out of the ball park. While, on balance several new stadiums are home-run-friendly (Colorado) others have dampened home runs (San Diego). Given the dramatic spike in home runs, I don’t believe this could have had more than a minor effect on home runs, and the effect would occur gradually.

4. Bats. Bat technology has certainly changed since I was a kid, when nearly every player used an ash bat made by Louisville Slugger. Maple bats, hardened with shellac, with tiny handles are the new weapon of choice for batters. Again, I think this fails to explain the home run spike in the early-1990s, because they trickled into the game. It could be a contributor, but it’s not sufficient on its own.

5. Strike zone. It’s possible that the league redefined the strike zone into a more-compact area to increase offense. However, recent attempts to expand the zone (with the help of computer monitoring) haven’t dampened offense.

There may be a few explanations that I have missed, and I’m open to others. But if you have another hypothesis, it must be able to explain the near-instant rise and subsequent plateauing of home run rates. I believe steroids fail this test miserably. I’m fine with the “home run era,” but in my mind steroids can only explain a very small part of why home runs increased during this time period.

11 Responses “What Caused the “Steroid” Era?”

  1. Millsy says:

    I think expansion would be the biggest culprit for the 1993/1994 spike.

    I’m more interested in the quick rise in 85-86-87 and the fairly sustained drop for the 5 years until expansion. I know there was an AL attendance spike here as well, but that was sustained through to the strikes in 94/95 (and shortly thereafter). Can we chalk 1985-87 up as noise? I’m not totally convinced that’s the case, given the 3 year trend and sudden drop. Do they look any different for the AL/NL? I honestly have no idea.

  2. Ron Elstun says:

    I love the research – one area that you may also consider is the use of contact lens. I see hitting as a matter of seeing the ball and hitting what you see. I remember one day when my son was playing ball in high school and went on hitting streak and he said, “I am seeing the ball so well right now.” You often hear hitters comment on the ball looking as big as a softball when they are on a hitting streak.
    I have thought for a long time that steroids would not help, but would hinder the swing of an athlete as they bulk up. And I have never heard anyone say that steroids helps the eye-hand coordination. You have to see the ball very well to hit a lot of home runs.

    May be the ball players are eating more carrots these days….?

  3. Millsy says:


    I’ve read (not necessarily from reputable sources) information regarding the idea that certain steroids can improve sight and hand-eye coordination. Don’t ask me to cite that though.

    As for the ‘bulking up’ getting in the way of a swing, I’ve seen others report this is a myth (again, this is just casual reading and searching around). Of course, that’s if you’re doing the right exercises and maintaining flexibility. The interaction of strength training improvements, understanding of flexibility, and using steroids could (I’ll bet) result in a net positive effect on hitting.

  4. I think it would be helpful to highlight all years in which MLB expanded on your first graph.

  5. Devon says:

    This’ll have my noodle cooking for a while. Love this kind of stuff.

  6. clayborne says:

    That expansion effect should be fairly easily tested. Did 1993 and 1998 show increases in line with the increased proportion of at-bats facing players who previously would not have been in the MLB?

    Looking at the graph, there is a big jump from 1992 to 1993, as would be expected from an expansion in 1993. However, there is a similar jump from 1993 to 1994 – a year after the expansion — while the expansion should just be a one-time structural break. Also, there is only a small increase from 1997 to 1998, which would not be expected if expansion is the cause. Two-teams worth of inferior players were in place in 1998, while there’s a big jump from 1998 to 1999.

    On the steroid issue, you’re talking about a diffusion rate of a technology in a population. You assume that it would be slow, which might match a diffusion in the general population. However, MLB is a small and close community, where workout routines could easily diffuse quickly. Further, the people who train MLB athletes is an even smaller community.

    Another test that would be interesting here is one you allude to: did HRs/SLG% increase across the entire league, or did it only increase in a subset of players? If the former, that suggests expansion. If the latter, it suggests steroid use.

  7. Michae lCoughlin says:

    Obviously all things are a combination of factors, but I think there could be an argument that it’s steroids and the rise of sabremetrically inclined front offices. Perhaps steroids were introduced and that explains the quick rise. MLB cracks down on ‘roid use. This should have depressed homerun totals, but it also happened along at the same time GMs – like Beane most famously – began to radically look at stats from a different, and IMO more correct, perspective. Had GMs been stuck in their old ways of thinking, relying more on imperfect stats like batting average and wins, maybe there would have been a drastic drop in homeruns. In other words, perhaps steroids “artificially” sped up a process that would eventually have arrived. Had we had a longer period of “smarter GMs” with steroids, maybe THOSE numbers would have been impossible to maintain and we’d see a drop. Kind of a “stupid” GM + steroids = smart GM without steroids.

    While the lack of steroids has seemed to depress the upper level of homerun totals (no one’s hitting 60 let alone 73) the smarter GMs, emphasizing OBP and SLG, have increased the output of the lower level of homeruns (spots in the order that would have once been hitting 10 homeruns because “stupid GMs” overlooked certain players are now hitting 15).

  8. James says:

    A couple of points I want to make in case you had not considered.

    1.) Does the “expansion” argument take into consideration the rise of foreign players as well. I saw one study that showed the number of Dominican players doubled in the Major Leagues between 1992 and 2005. Also the Asian-born players began to play more and more in the Major Leagues. This could offset the “dillution” of talent.

    2.) Baseball seems to be a tightly knit fraternity. players know each other so it wouldn’t be surprising if the “steroid bug” spread quickly among them. They would need a catalyst though, and it may have come in 1990 when a virtual unknown (Cecil Fielder) made waves by hitting 50+ home runs, and was eventually rewarded with a hefty contract. Coupled with the fact that Canseco (already probably juicing) was awarded the highest contract in 1991 may have started the ‘roid trend.

    3. The “live ball” theory was used to explain the 1987 season where there was an abnormal spike in home runs (McGwire hit 49 that year). This theory was proposed again during the 1990s, I read a news article then that stated that MLB baseballs were only made in two factories, one in the Dominican Republic I believe. The owners swore they were not “jucing” the ball. I don’t know if that is accurate or not, but I think it has been looked into.

    4.) Expansion could explain for part of it. The previous expansion year (1977) did see one 50 home run hitter, George Foster, (the only one between Willie Mays’s 52 home run year in 1965 and Fielder’s 1990 season) but it was in the NL not the AL. Only the AL expanded that year so Foster did not hit any expansion pitching.

    Home runs per game increased in both league in 1977 at the same rate, then the year after expansion the NL rate dropped to .65 per game (from roughly .84) and the AL rate dropped to .74.

    Anyway it may be a combination of expansion and steroids, though I don’t know that expansion had that much of an effect on the game, given that the last expansion year did not produce a significant amount of home run hitters.

  9. Giri Guevara says:

    Can you do one for International Cricket please. Number of runs scored in One Day Internationals or Test Matches

  10. adam block says:

    There are a number of contributing factors to baseball’s Steroids Era. I discuss them in my undergraduate thesis called baseball’s dark cloud.



  1. […] This post was mentioned on Twitter by J.C. Bradbury, Capitol Avenue Club. Capitol Avenue Club said: Required Reading from @JC_Bradbury – What Caused the "Steroid" Era? | Sabernomics — http://bit.ly/9HyjTM […]