One of the hallmarks of Ryan Dempster’s second life as a starter has been durability. But what is the likelihood that he will continue to demonstrate that trait over the course of the two-year, $26.5 million contract with the Red Sox that the pitcher and team officially announced on Wednesday?

To figure that out, it’s necessary to note what Dempster did in recent years to position himself for the deal he just signed. Since he left behind his career as a closer for the 2008 season, Dempster has gone 65-49 with a 3.74 ERA and a sturdy 997 innings, a workload that ranks 18^th in the majors in that time. He’s one of five pitchers in the big leagues with five straight years of at least 170 innings pitched.

In 2012, Dempster fell below the 200 innings threshold for the first time in that run, delivering 173 frames for the Cubs and, after his mid-year trade, the Rangers. Still, while he fell below the mystical 200-innings threshold in 2012, he’s one of 15 pitchers with at least 200 innings pitched in four of the last five campaigns.

Dempster views the ability to log innings, to shoulder his share of a starter’s burden and to alleviate the strain on a bullpen, as one of the defining aspects of his job.

“I think that that’s your responsibility as a starting pitcher in the big leagues,” Dempster said at his introductory press conference on Wednesday. “The norm used to be 300. Somehow, we’ve worked it down to 200 or even 180 seems to suffice.

“[But] I work extremely hard in the offseason and during the season to try to keep myself as healthy as I possibly can so that I can take on that workload. It’s something that I pride myself in,” he continued. “As a starting pitcher, we only get to contribute once every five days. I pride myself on trying to contribute as much as I can, if you can take the brunt of it off the bullpen. And also, too, I think it pushes other pitches on your staff. Friendly competitiveness is nice -- pushing each other to be better, go out and get as much out of each other as we can.”

Certainly, Dempster’s appeal for the Sox was two-fold, found both in the fact that he’s been effective and durable. The team wanted to add a stabilizing presence to a rotation that had just two pitchers (Jon Lester and Clay Buchholz) who threw as many as 180 innings. The daily inconsistency of the starters made it extremely difficult for the team to go on any sort of run when it was still in the race for a playoff berth through the early days of August.

“It’s important,” Red Sox GM Ben Cherington said of Dempster’s durability. “Ryan’s got a history of being very effective and a really good pitcher. The consistency he’s shown in terms of taking the ball every fifth day was important to us.

“I think, as a team, when you start having to fill in for guys, if we don’t have a reliable rotation and you start filling in with guys from down below or moving guys from the bullpen or whatever, it’s not so much that move but you’re inevitably weakening another area of your team. It’s no secret, our best teams generally have been ones where we’ve had pretty good reliability in the rotation. We’re certainly trying to build that again here.”

But is it realistic for the Sox to expect Dempster to do that?

After all, the right-hander is now 35 years old, and turns 36 in May. He’s already shouldered more than 2,000 innings (2,215 2/3, to be precise) in his career. So, it seems appropriate to ask -- what is the likelihood that Dempster will remain durable during the deal that he just signed?

To figure out the answer, it’s worth looking at the group of pitchers who proved comparably durable to Dempster during the five-year stretch that he just concluded. Dempster is the 47th pitcher in the last 50 years to have five straight seasons of at least 160 innings pitched between those ages.

Of those, three (Dempster, A.J. Burnett and Bronson Arroyo) are active and just turned 35. Another (Ted Lilly) is active and just concluded his age 36 season.

Of the remaining 43 pitchers, how did the group do in terms of remaining durable at ages 36 and 37?

Fewer than half (19 of 43, 44 percent) had two seasons of 160-plus innings at ages 36-37. About 21 percent (9 of 43) had one season of 160-plus innings. And more than a third (15 of 43, 35 percent) did not have a 160-inning season at either age 36 or 37. In other words, it should come as no more surprising to the Sox if Dempster fails to reach the 160-innings threshold in either of the next two years as it would if he surpassed that mark in both 2013 and 2014.

Overall, the group of pitchers that remained durable between the ages of 31-35 saw little dropoff in the quality of their innings. The group saw a reasonable but not disconcerting 9 percent rise in its ERA (from 3.48 to 3.76), resulting in a slight drop in ERA+ (ERA relative to league average) from 114 to 108.

So, the “Dempster group” is typically effective at ages 36-37, but with a decreased likelihood of remaining healthy. On average, the group saw its annual innings load drop by 28 percent, from an average of 228 per season to an average of 164 per season.

Still, does that make Dempster a bad bet on a short-term contract? Would the Sox have been better off, perhaps, making their bet on a younger free agent pitcher like Zach Greinke or Edwin Jackson or Anibal Sanchez?

To get a sense of that, it’s interesting to see how pitchers who were durable between ages 26-30 held up over the next two years of their careers. Is there a considerably greater chance of getting two healthy seasons out of younger pitchers who have been as durable as Dempster?

In the last 50 years, there have been 91 pitchers who have logged at least 160 innings in five straight years between ages 26-30. While that ensemble remained more durable than the older “Dempster group,” the difference wasn’t quite as pronounced as one might expect.

Of those 91 pitchers, two (James Shields and Paul Maholm) just finished their age 30 seasons, and two more (Dan Haren and CC Sabathia) just finished their age 31 seasons.

Of the remaining 87, slightly over half (46 of 87, 53 percent) had two seasons of 160-plus innings at ages 31-32. Another 23 percent (20 of 87) had one season of 160-plus innings in those two years, while the last 24 percent (21 of 87) fell short of 160 innings at both ages 31 and 32.

In other words, there’s a marginally better chance that younger durable pitchers will remain durable than will pitchers at Dempster’s career stage. But when one considers that the younger pitchers will often get much longer contracts -- witness the six-year deal for Greinke, the five years that Sanchez got from the Tigers, the reports that Jackson is weighing four-year offers, etc. -- the idea of Dempster on a two-year deal seems like an entirely reasonable proposition.

All pitchers represent increasing risks over time. Past health doesn’t guarantee future health, as virtually every shoulder and elbow has a time bomb that is destined to go off at some uncertain point.

The pitchers who were healthy enough to log five straight years of 160 innings between the ages of 26 and 30 saw an average annual decrease in their innings of 22 percent at ages 31 and 32. They saw their ERAs rise by 9 percent, an increase virtually identical to that of the age 31-35 group of durable starters.

In other words, if a team has the opportunity to choose between a two-year deal for a 35-year-old pitcher who has been durable, or a three- or four- or five- or six-year deal for a 30-year-old pitcher who hasn’t been as durable, the choice is fairly straightforward. For a shorter-term deal that entails considerably less risk of a payroll albatross, a team can acquire a pitcher who is almost as “safe” a bet to remain healthy for two subsequent years.  

That rationale helps to explain why Dempster is now a Red Sox pitcher.