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Introducing the Harbaugh Index, A New College Football Performance Metric

A handy way to judge how Michigan your team is

Ohio State State v Michigan Photo by Leon Halip/Getty Images

The advanced stats revolution in sports keeps rolling and this time it’s rolled all the way to the bastion of traditional football purism that is Off Tackle Empire.

There’s nothing more important to us, however, than being able to tell you the stories of the Big Ten, and advanced stats can help us do that. To this end, we’re proud to unveil a new one: the Harbaugh Index!

The Harbaugh Index is based on Bill Connelly’s SP+, and what it measures is how much your team is like the Jim Harbaugh Michigan Wolverines. Through five years, Harbaugh has established above all the following two tenets of Michigan Football:

  1. Never lose to an inferior team
  2. Never defeat a superior team

In this way, Michigan has become the gatekeeper to the ranks of the elite. This could also have applied to Iowa under Kirk Ferentz, but they’ve been prone to the occasional bout of volatility. The Hoosiers have been wrongfully described as the Chaos Team; Michigan represents the ultimate Order Team. The Stay In Your Lane team, if you will.

How It Works

The Harbaugh Index has two components: ranked (RHI) and scored (SHI). For Michigan, for instance, RHI is calculated as follows:

(Highest SP+ rank of a team Michigan defeated) - (Lowest SP+ rank of a team that defeated Michigan)

19th-ranked Notre Dame is Michigan’s best win by SP+, and 12th-ranked Wisconsin is their worst loss. This means Michigan’s RHI for 2019 is 7

Michigan’s SHI calculated as follows:

(Lowest SP+ score of a team that defeated Michigan) - (Highest SP+ rank of a team Michigan defeated)

This yields a Michigan 2019 SHI score of 4.2

What Does It Mean?

The Harbaugh Index is a numerical difference between a team’s best win and worst loss. The significance of this is in evaluating how Harbaugh the team is. As mentioned previously, Michigan is the gatekeeper to the group of the elite. This doesn’t necessarily mean that they exist in no-man’s-land between the great teams and the also-rans, but the teams they defeat are a distinct tier lower than the teams they lose to. Michigan stays right the hell in their lane. This is a double-edged sword: you know you’re going to get a baseline of around 8 wins, but the next level can seem so far away. Nevertheless, a positive Harbaugh Index is a key indicator of a Solid Program.

Solid programs are not, however, fun for the casual observer. This whole metric was inspired by an idea I had for an MS Paint Infographic about Illinois being the objective most fun team in the conference, possibly in the country.

I posited that Illinois probably had the biggest gap between their best win and their worst loss, and then realized that in fact, not every team beats a better team and loses to a worse team in the same year. In fact, some teams just refuse to ever do either of those!

This doesn’t necessarily mean that a Harbaughish team cannot defeat a team ranked higher or lose to a lower-ranked team. SP+ is, after all, inexact. However, the signature of the Harbaugh Index is not about your wins and losses relative to your team’s strength, it’s about the separation between the groups of teams you beat and teams you lost to. When there’s no overlap and a clear gap, you have a Harbaugh situation.

How It Applies To The Big Ten

I ran these numbers for every Big Ten team and here’s what I came up with

Big Ten Harbaugh Index 2019

Ohio State Buckeyes 8 infinite
Michigan Wolverines 7 4.2
Indiana Hoosiers 10 4
Iowa Hawkeyes 7 3.9
Maryland Terrapins 10 2.8
Rutgers Scarlet Knights -9 -1.5
Penn State Nittany Lions -7 -4
Nebraska Cornhuskers -13 -4
Northwestern Wildcats -15 -4.1
Minnesota Golden Gophers -12 -7.4
Michigan State Spartans -35 -12.5
Purdue Boilermakers -60 -15.3
Wisconsin Badgers -48 -20.4
Illinois Fighting Illini -89 -30.3

Ohio State doesn’t entirely count due to having no losses.

Michigan has the highest rational SHI, as expected.

If not for their loss to Michigan State, Indiana would be the ultimate Big Ten Order Team. As it stands, they’re still pretty Harbaughish. Indiana fans have been arguing for years that #ChaosTeam is a misnomer, as they always reliably lose to elite teams. Here’s your proof, Hoosier faithful.

Iowa is of course what Michigan is based on, so it’s only natural that they’d put up nearly identical numbers.

What surprised me was Maryland having a positive Harbaugh Index. In retrospect, Syracuse is indeed worse than Purdue and headed up the small group of teams Maryland beat. Harbaugh Index can also be bleak.

A negative Harbaugh Index that’s nevertheless close to zero indicates near-stability. Rutgers‘ win over Liberty Flames apparently beats their loss to Maryland. Yikes, Maryland!

Nebraska had their high point in defeating Illinois. Yikes! Still, it didn’t get worse than losing to Colorado.

Penn State found themselves in the negative Harbaugh Index numbers due to their loss to Minnesota.

Northwestern nearly had a nice positive Harbaugh Index by virtue of their win over UNLV, but then they had to go and beat Illinois and get some overlap with their Stanford loss.

The Gophers reached above where they were but also fell back to the ground the next week. This volatility is reflected in their Harbaugh Index.

Naturally, Michigan State shows up near the chaos end of the spectrum. In hindsight, Indiana was the real Program Win. It’s by far the best item on their resume.

Purdue made their way towards the bottom of this index by virtue of losing to 112th-ranked Nevada but still beating Nebraska

Wisconsin Badgers, of course, had a LOT of help getting to this point. It’s out of character for them to show up here.

And of course, Illinois with what has to be the lowest Harbaugh Index in the country. From losing to Eastern Michigan to knocking off Wisconsin, nobody’s been more unpredictable.

See what you can find outside the Big Ten!