By Manny Randhawa

The debate over just how exclusive the National Baseball Hall of Fame should be is as old as the institution itself. Currently, 1.2 percent of all players in MLB history have been enshrined in Cooperstown. But given current trends, that percentage could very well increase.

In a new era of player evaluation, where advanced metrics enable us to more clearly see dimensions of a player who would previously have been overlooked, the probability that a higher percentage of players will eventually be elected is rising. In addition, the changing composition of the Baseball Writers' Association of America voter pool will likely further propel this movement.

The trend is evident in the significant increase in vote percentage of several players over the past few years, not to mention the election of Tim Raines in 2017. And with 42.2 percent of this year's balloting tracked by Ryan Thibodaux, a trio of candidates that have historically fallen well short of election are surging thanks to a more in-depth study of their careers afforded by advanced metrics.

Part of the reason for this surge, of course, is that BBWAA voters are limited to 10 selections each year, and sometimes hard choices are made to leave off players who might otherwise have been chosen. But with this trio, there appears to be more to it than that.

Mike Mussina

This is Mussina's fifth season on the ballot. His vote percentage has gone from 24.6 percent in 2015 to 43 percent in '16 to 51.8 percent last year. That represents a 70 percent increase in vote total from 2015-17. So far this year, Mussina is polling at 73.2 percent, just below the 75 percent threshold for election.

Mussina doesn't check off many of the traditional boxes that have been considered for inducting a starting pitcher into the Hall of Fame: He did not win 300 games (270), a mark that has become a pseudo-prerequisite dating back about 30 years. And he did not win a Cy Young Award (finishing in the top five six times). But over an 18-year career, Mussina put up numbers worthy of Hall of Fame induction.

Mussina posted a career 3.68 ERA despite spending his prime in one of the highest-scoring run environments in history. His career ERA+, adjusted for ballpark and ERA across the league, is 123 (higher than that of Hall of Famers Bob Feller, Don Drysdale and Warren Spahn, among others). And from 1996-2001, a six-season span over which five of the top 10 offensive seasons (in terms of runs scored) ever took place, Mussina's ERA+ was 126.

There were only seven starting pitchers (min. 750 innings pitched) in the same period who had lower fielding-independent pitching than Mussina's 3.46: Pedro Martinez, Randy Johnson, Kevin Brown, John Smoltz, Greg Maddux, Curt Schilling and Roger Clemens. Mussina had a career 3.57 FIP, ahead of his contemporary Tom Glavine's 3.95. Glavine was inducted into the Hall of Fame in 2014.

Per Jay Jaffe's JAWS rating, Mussina (83.0) ranks 28th among starting pitchers all-time. Of the 27 ahead of him on the list, 24 are in the Hall of Fame, and two are Clemens and Schilling. The average Hall of Fame starting pitcher's JAWS rating is 62.1, and there are 41 starters in the Hall of Fame with a JAWS rating lower than Mussina's.

It appears Mussina is finally on the verge of election, and with his eligibility on the BBWAA ballot only halfway exhausted, he should eventually get in if he doesn't this year.

Edgar Martinez

There's been a big social media push for Martinez, who is on the ballot for the eighth year. And why not? After all, the award for each season's most outstanding designated hitter isn't named after the Mariners great for nothing.

Therein lies the reason Martinez hasn't yet been inducted: He was a DH for most of his career, and not playing in the field disqualifies him for many voters. But Martinez was one of the most valuable hitters of the 1990s. Over that decade, only six players had a higher WAR than Martinez's 51.6: Barry Larkin (52.4), Frank Thomas (52.7), Craig Biggio (52.9), Jeff Bagwell (56.7), Ken Griffey Jr. (67.3) and Barry Bonds (79.9). All but Bonds are in the Hall of Fame.

Only four players during that decade had a better wRC+ than Martinez's 154: Bonds (172), Thomas (166), Mark McGwire (165) and Bagwell (158).

In 1995, Martinez finished second among all American League position players in WAR at 7.0 (the highest single-season WAR produced by any DH). Considering the positional adjustment for a DH (-15 runs per Baseball Reference) and the arguably more difficult task of hitting off the bench every game instead of hitting after playing in the field, that '95 campaign exemplifies just how elite a hitter Martinez was.

Martinez, too, has gained substantially in Hall of Fame balloting over the past three years. In 2015, he received 27 percent of the vote. That percentage swelled to 58.6 percent last year. And with nearly half the vote accounted for in Thibodaux's ballot tracker this year, Martinez is at 80.4 percent in his ninth year of eligibility. Voters are coming around, and it's in large part thanks to advanced metrics.

"People are taking a different look about the DH and the sabermetric numbers and taking into consideration all those numbers, and it's helping my case," Martinez told Seattle reporters on a conference call after last year's results were revealed.

Larry Walker

Like Martinez, Walker is running out of time, with his eligibility on the BBWAA ballot down to two more years after this one. But unlike Martinez, Walker is unlikely to see enough of an increase in support to cross the 75 percent threshold in that short window.

Nevertheless, Walker's vote percentage has gone from 21.9 percent to 39.1 percent in the past year. Why? Many voters are looking to park-adjusted numbers and finding that the narrative of Walker being largely a Coors Field creation is false.

Yes, Walker spent a decade playing home games in the thin mountain air of Colorado, which resulted in inflated offensive statistics. But when park adjustments are made, he's on par with Chipper Jones. Those two have an identical 141 OPS+ (adjusted for ballpark) for their careers, and each was a National League Most Valuable Player Award winner, two seasons apart. Jones, however, currently has 98.3 percent of the vote in his first year of eligibility.

So far, we've only taken into account Walker's performance at the plate. He was a good base stealer in the prime of his career, swiping 189 from 1990-99 and 230 overall. Defensively, there weren't many better right fielders when Walker played, as evidenced by his seven Gold Glove Awards.

Walker's 1997 season, for which he was named NL MVP, is a microcosm for the argument that he is deserving of the Hall of Fame: He slugged .709 at Coors Field, but he slugged .733 on the road.

More than the "Hall of Very Good"

What this trio of Hall of Fame candidates and their surge on this year's ballot indicate is that more voters are using in-depth tools now at their disposal to evaluate who belongs in Cooperstown. That's a good thing.

Many argue that making the Hall less exclusive is somehow watering it down and transforming it into the "Hall of Very Good" rather than the Hall of Fame. But what if in the past, limited to the aid of traditional stats to determine who was worthy of inclusion, we left some deserving candidates out?

A larger group of Hall of Famers resulting from increased utilization of advanced metrics wouldn't change the nature of the Hall of Fame into something lesser. It would only serve to mold the Hall of Fame into a hallowed museum more inclusive of the greatest players in the game's history.

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Manny Randhawa is a reporter and member of the Statcast™ research team at MLB.com. You can follow him on Twitter @MannyOnMLB.