He's a big believer in the advanced metric Fielding Independent Pitching, or FIP, which focuses only on what the pitcher can control without the help of his teammates. It essentially calculates what a pitcher's ERA should look like based on strikeouts, walks and home runs allowed.
So Perkins knows that if he performs well in those three categories, he's doing his job and traditional statistics such as ERA will eventually fall in line with his FIP.
"Fielding independent pitching is the main stat I worry about," Perkins said. "I know I don't want to give up home runs, don't want to walk guys and I want to get strikeouts. So I know the process."
Perkins is well-aware it's a rarity for a player to be so into sabermetrics, but says that more and more players are interested in what's out there. Perkins, who has always maintained he'd be a math teacher if he wasn't a baseball player, now serves in that role to his teammates, as they'll come up to him and ask him about their own advanced statistics and what they mean.
"People ask me all the time about this guy or that guy and people ask me what their stuff means," Perkins said. "They like to know where they're at. My most frequently visited site is Fangraphs and I can't imagine it's the same for anyone else."
Perkins, 31, is having another solid season measured by traditional statistics, as he's posted a 2.72 ERA with 27 saves in 29 chances. He's also struck out 57, walked just eight and served up just two home runs 46 1/3 innings en route to being named an All-Star for a second straight year. But with the help of Perkins, here's a look at five of his favorite advanced statistics and how he stacks up this season:
Statistic: Fielding Independent Pitching (FIP)
Perkins in 2014: 1.83
Perkins in 2013: 2.49
Perkins for his career: 3.80
Perkins' take: "I know that I want to avoid home runs, strike guys out and not walk guys. If I can do that, and maybe even get a groundball, and even that it's that important to me as not walking a guy and those things. As long as I don't walk guys and don't give up home runs, I know I'm doing the right thing. It's the culmination of a lot of things, but I know if I can keep that down, my ERA is going to be there eventually."
Analysis: Perkins' 1.83 FIP is a career-best and better than his 2.49 mark last season. Perkins has struck out a career-high 11.07 batters per nine innings, while also setting career-bests with 1.55 walks per nine innings and just 0.39 home runs allowed per nine innings. But due to what can be described as some bad luck in other advanced metrics, Perkins' 2.72 ERA is his worst since 2010. The left-hander had a 2.30 ERA last season.
Statistic: Batting average on balls in play (BABIP)
Perkins in 2014: .336
Perkins in 2013: .271
Perkins for his career: .305
Perkins' take: "I know it's way up there this year. It's about 60 points higher than last year. I think I've given up as many hits as I did all of last year. But I don't think my batted ball profile has changed all that much. Balls are finding holes and falling into the outfield or whatever. But it all evens out."
Analysis: One of the key theories of defensive independent pitching statistics is that pitchers don't have control over the balls that drop in for hits. Perkins concedes pitchers can generally control whether they're groundball or flyball pitchers, but that it's out of their control whether balls hit are turned into outs. The league average for pitchers on balls hit into play is generally about .300, so Perkins is running into some tough luck this season after being helped by a .271 BABIP last season.
Statistic: Left on base percentage
Perkins in 2014: 69.7 percent
Perkins in 2013: 83.3 percent
Perkins for his career: 73.7 percent
Perkins' take: "I know it's lower and it's a reason why my ERA is higher, especially because I'm not really giving up home runs. I haven't done as good of a job stranding runners. But again, if I don't walk guys, I gotta give up a couple hits, so I think the biggest thing is not to give them baserunners. And I've done a good job of that this year."
Analysis: Also known as strand rate, the statistic takes a look at how often a pitcher leaves runners on base over the course of a season. The league average is generally 72 percent, so Perkins is slightly worse than that this season after getting some good fortune last year with a career-best 83.3 percent strand rate.
Statistic: Swinging strike percentage
Perkins in 2014: 12 percent
Perkins in 2013: 13.1 percent
Perkins for his career: 9 percent
Perkins' take: "I'll check in periodically to see what my swinging strike rate to make sure that the strikeouts I'm getting are sustainable. You obviously have to get swings and misses."
Analysis: It's a fairly simple statistic as it simply measures what percent of a time an opposing batter swings and misses at an offering. The league average is roughly 8.5 percent, so Perkins fares well at getting swings and misses, especially with his slider, but his rate is slightly down from last year.
Statistic: Line drive percentage
Perkins in 2014: 22.2 percent
Perkins in 2013: 26.2 percent
Perkins for his career: 20.2 percent
Perkins' take: "If my batted ball profile hasn't changed -- line drives fall in for hits the most often -- and I'm not giving up as many line drives as last year, I'm not concerned."
Analysis: Line drive percentage is part of a batted ball profile that also includes groundball percentage and flyball percentage. Perkins knows he can't control how many balls fall in for hits, but he can see how often batters are squaring up his pitches based on this statistic. He's actually giving up a lower percentage of line drives this year than last season, even though his batting average on balls in play is more than 60 points higher.