In keeping with the recent theme, I’d like to take another look at RBI as a statistic. Recently, I’ve shown you why RBI can be misleading when comparing two players’ value and why having a lot of RBI doesn’t necessarily mean you had a good season. To catch up on these and other similar posts about baseball statistics, check out our new Stat Primer page.
Today, I’m turning my attention to RBI over entire careers. You’ve seen already that RBI aren’t a good way to measure players in individual seasons, but we’ve yet to see how well they do at explaining value in very large samples. The answer is not much better.
To evaluate this, I took every qualifying player from 1920 (when RBI became and official stat) to 2013 (2,917 in all) and calculated their career RBI rate by simply taking their RBI/Plate Appearances. This will allow us to control for how often each player came to the plate so Babe Ruth’s 10,000 PA can go up against Hank Aaron’s nearly 14,000. Next, I compared that RBI Rate to wRC+ (what’s wRC+?) which is a statistic that compares offensive value to league average while controlling for park effects. The simple explanation is that wRC+ is a rate statistic that controls for league average, meaning that a 110 wRC+ means the same thing in 1930 as it does in 1980. League average is 100 and every point above or below is a percent better or worse than league average in that era.
The results aren’t great for RBI as an individual statistic. Overall, the adjusted R squared is .4766 which means that about 48% of the variation in wRC+ can be explained by variation in RBI Rate. Put simply, players who have more RBI per PA are better hitters on average than those with fewer, but there is a lot of variation that isn’t explained by RBI Rate meaning you can’t just look at RBI and know how good a player was.
What this graph is showing you is quite striking. First, notice how many players have similar RBI Rates who have wildly different wRC+ and second notice how players with the same wRC+ have wildly different RBI Rates. Generally more RBI mean you’re better, but there’s a lot left unexplained by this stat.
Like I’ve said before, RBI isn’t a made up stat that is useless like wins for a pitcher because RBI reflects a real event on the field and is critical for score keeping. The problem with RBI is that it is too dependent on context and the team around you. Two players who are equally good on offense can have very different RBI Rates because they have a different number of opportunities to drive in runs. Similarly, players who drive in the same number of runs may be much different offensive players in terms of quality.
Even if you’re someone who thinks clutch hitting is a predictive skill, surely you can recognize that RBI is extremely context dependent. Your RBI total depends on how good you are, but also how many runners are on base, how many outs there are, and where the runners are positioned on the bases – all of which you have no control over as a hitter.
I’m on the front lines of the #KillTheWin movement, but I don’t think we should kill the RBI. The RBI just needs to be put in proper context and understood as a descriptive stat and not a measure of player value. Miguel Cabrera gets a lot of RBI, partially because he’s awesome, but also because his team gets on base in front of him all the time. Driving in runs is an important part of winning, it just isn’t an individual statistic. It’s a team statistic and we should view it as such.
You’ve seen that RBI can mislead you when comparing two players, that bad players can have a lot of RBI, and now you’ve seen that this isn’t something that evens out over time. RBI is simply not a good way to measure individual value when it can tell you the wrong thing this much of the time. There are better ways to measure the same concepts like wOBA, wRC+, and wRAA. Feel free to click on the links to learn more and check back for more on why you should put less stock in RBI.