In the world of sports, the catcher position is kind of weird. Catchers start each play out of bounds, facing a different direction than their teammates. On a more micro level, baseball’s most important in-bounds/out-of-bounds determination, the strike zone, isn’t static as it is other sports; it’s determined on every pitch, and the catcher has a role in making that determination. In a non-contact sport, they’re covered in protective armor. Those of us with lousy knees are in awe just of their ability to do all that squatting.

Catcher is also the only position on modern rosters where there is planned redundancy. Thirteen-man pitching staffs have more or less eliminated platoon tandems, but catching tandems persist. The Pirates don’t carry an extra center fielder to give Andrew McCutchen a rest in the second game of doubleheaders. The Nationals don’t have a second right fielder to play instead of Bryce Harper on day games after night games. The Yankees don’t roster a spare third baseman in case Chase Headley gets hurt or tossed from a game. But every team has to have two catchers, and each of them sees a decent amount of playing time. (The catchers for the above three teams in particular, as we’ll see.)

Further, the impact of a catcher injury can be significant. A disabled catcher’s replacement could well be unfamiliar with his pitching staff and opposing hitters’ tendencies, impairing his ability to call a game. He may not know the league’s umpires and their interpretation of the strike zone. He might not be up to speed on his infielders’ shifting tendencies and how that may affect pitch selection and location. And his presence probably means extra work, and extra fatigue, for the team’s other catcher. Just ask a Boston Red Sox fan about the importance of healthy catchers. (That’s a rhetorical suggestion. I don’t recommend actually doing that, unless you want to hear a long exposition about the importance of good free agent signings, a reliable starting rotation, offensive production from your first basemen, keeping your closer and second baseman off the DL…really, it can go on for a while.)

This summer, while attending a Phillies-Pirates game during which the Pirates used both of their catchers, my friend wondered whether the Pirates had the skinniest catchers in the league. (Francisco Cervelli is listed at 6’1″, 205, Chris Stewart 6’4″, 210). While actually putting in the time to figure this out (the answer appears to be “yes,” if you can trust listed heights and weights), I noticed that Cervelli and Stewart had caught all but 17.1 innings for the Pirates in 2015. This was in August, but it remained the case for the entire year. Cervelli caught 1099.2 innings and Stewart 372.2. Combined, that represented 98.8% of all the Pirates’ defensive innings last year. This struck me as notable, as the Pirates had lost the durable Russell Martin to free agency over the winter, replacing him with Cervelli, who’d never played more than 93 major league games in a season previously. The Pirates are famous for their use of analytics, including monitoring player health, with an eye toward injury prevention. Maybe that’s working. Or maybe they’ve figured out something with skinny catchers. Either way, I wondered whether the Pirates’ tandem represented something unusual.

To check, I looked at every team’s catchers since the 1969 start of divisional play. Using this year’s Pirates as my model, I looked for teams for which the top two catchers caught 98.5% or more of all innings. Last year, the average team’s catchers caught 1,446 innings, so I was looking for teams whose top two catchers were on the field for all but 21.2 innings, on average.

It turns out the Pirates weren’t unique. Brian McCann and J.R. Murphy caught every inning for the Yankees this year. Wilson Ramos and Jose Lobaton caught all but nine innings for the Nationals. Carlos Ruiz and Cameron Rupp were behind the plate for all but 18 innings for the Phillies. That’s about typical. Since 1969, there have been 240 teams whose top two catchers caught at least 98.5% of all innings during the season, or a little over five per year (closer to four and a half if you exclude strike-shortened seasons).

But totals don’t tell the whole story, since baseball’s expanded from 24 teams in 1969 to 26 in 1977, 28 in 1993, and 30 in 1998. The graph below shows the percentage of teams, per season, with two catchers handling 98.5% or more of the workload. The overall average is 18.6%. There’s a very slight downward trend to the line–the slope is -0.03% (yes, I got the decimals right)–meaning that catchers have been becoming a little less durable over the years, but almost imperceptibly so. (I was tempted to say “a little less durable, or managers are giving them more rest,” but other than the occasional Kyle Schwarber, who primarily plays another position but can catch in a pinch, teams just don’t carry three catchers anymore, so rest for one catcher in a tandem means playing time for the other.)

(The outlier on the high side is 1994, when there were only 117 games played.)

Teams for which two catchers caught 98.5%-plus of innings won, on average, 85 games during the non-strike-shortened seasons. That’s not super impressive, considering the selection bias inherent in this sort of analysis. Specifically, teams with two catchers handling virtually all of the time behind the plate are teams that not only avoid catcher injuries, but also have two catchers good enough that they’d want to have them there all year, contributing to overall team success. In 2014, for example, the Red Sox had three catchers with over 400 defensive innings, in part because none of them could hit: A.J. Pierzynski (540 innings, .233 TAv), Christian Vazquez (458.1 innings, .239 TAv), and David Ross (418.1 innings, .230 TAv). (See, I told you not to ask a Red Sox fan about catchers.)

Still, 85 wins is decent, four games better than .500–that’s the Angels this year. Of the 213 teams for which two catchers caught 98.5%-plus innings in non-strike-shortened years, 77, or 36%, won 90 or more, which is generally good enough to get you into the postseason these days. So there’s certainly an advantage to getting all the work out of two catchers.

So has anybody cracked the code on keeping their two catchers healthy? I looked for teams that had three or more seasons in a row with two catchers handling 98.5% or more of innings. If teams have a secret sauce, they should show up on this list with regularity:

Nope. The closest thing there is the Yankees, who had streaks with Thurman Munson in the 1970s and Jorge Posada around the turn of the century. The only other teams to appear more than once are the Johnny Bench Reds and two iterations of the Pirates, over a decade apart and 30 years ago. There’s nothing in this table suggestive that it’s a matter of skill, rather than luck, to keep two catchers on the field all season. Specifically, these teams generally had an All-Star caliber No. 1 catcher who avoided injury with various guys in the backup role. That’s about it. No team has cornered the market on that formula.

So maybe that’s making the criteria too tough. Maybe I should be looking just at back-to-back 98.5%-plus inning performances. Given that, on average, 18.6% of teams had two catchers with 98.5%-plus innings caught since 1969, random chance suggests that a team with two dominant catchers has about a one-in-five chance of repeating the following year, like flipping a coin that comes up heads 18.6% of the time. A rate of repeat significantly above that could indicate skill rather than luck. Of the 236 teams, 1969-2014, that had two catchers with 98.5%-plus innings caught, 60 repeated the following year, or 25%. That’s not a statistically significant difference (using an N-1 chi-square test, if you were wondering). In other words, there’s no reason to believe that a durable catcher tandem is a matter of anything but good fortune.

So feel good about keeping your two catchers healthy this year, Yankees, Nationals, Pirates and Phillies. Especially the Pirates (.273 TAv) and Yankees (.267 TAv), who got above-average offensive performance from their catchers as well. (The Phillies and Nationals catchers, each with a .230 TAv, were among the worst in baseball.) Just don’t assume you’ll be able to keep those two guys on the field all of 2016 as well.