Depth ratio, as formulated last June:

Depth Ratio = (minutes played by top two players) / (minutes played by 8th and 9th players)

This ratio allows us to compare a single number across different teams and captures two key aspects of having depth:

• Not relying too heavily on one or two players to play nearly all of the minutes in important games, thereby reducing their ability to defend, rebound, and push the ball in transition with the intensity Izzo prefers.
• Having enough bench players to allow everyone to play hard every minute they’re on the floor and be able to deal with foul trouble. Nearly every basketball team has to have seven guys who play significant minutes (five starters plus one perimeter bench player and one interior bench player). Having two more bench players you can count on is what sets a good Izzo team apart from other teams.

As applied to Izzo-era Michigan State basketball teams, the magic number turned out to be 3.00.  Teams with ratios below that number have hung some banners at Breslin.  Teams with ratios above that number, not so much.

Would the magic depth ratio rule hold for the 2008-09 season?

In the immortal words of Marv Albert: Yes!

Now you could argue that MSU's depth ratio was somewhat artificially deflated since the #9 player, Marquise Gray, received extra playing time due to Goran Suton's injury early in the season.  But the team also had a #10 player, Korie Lucious, who averaged 9.0 minutes/game.  This was a classically-deep Tom Izzo team.

Here's how the players on last year's team stacked up in Minute% compared to the prior year's team, along with a projection of the top ten players for the upcoming season.

Going from 2007-08 to 2008-09, Kalin Lucas stepped up to fill Drew Neitzel's shoes as the 30-minutes-per-game guy, with Korie Lucious becoming the back-up point guard option.  Delvon Roe, with help from Draymond Green, replaced Drew Naymick.  And the #8 and #9 guys from the 2007-08 team, then-freshmen Chris Allen and Durrell Summers, became 20-minutes-per-game players.

In other words: Freshman contributed real minutes right off the bat, and sophomores weren't freshmen any more.

Going into the 2009-10 season, those same two things need to happen.  Roe and Green need to suck up the bulk of the minutes Goran Suton is leaving behind, while Korie Lucious fills in at least some of Travis Walton's minutes.  At the bottom of the PT spectrum, some combination of Tom Herzog (who is, in some sense, a 4th-year freshman), Garrick Sherman, and Derrick Nix will need to fill those crucial 8th and 9th spots in the rotation.

A lack of interior depth has sunk Spartan basketball campaigns before:

• 2001-02, following the graduation of Andre Hutson and the early entry of Zach Randolph into the NBA draft.
• 2003-04, following the graduation of Aloysius Anagonye and the early entry of Erazem Lorbek into . . . wherever it is he entered.

In both cases, young post players (Jason Andreas and Adam Wolfe as sophomores in 2001-02, Drew Naymick and Delco Rowley as freshmen in 2003-04) were unable to fill the void down low.

Hopefully, absent injuries, this season won't parallel either of those two situations.  There's only one starter-level post player to replace.  And Herzog and the two freshmen are already showing more signs of being able to contribute than the guys in parentheses in the previous paragraph were in a position to during the early stages of their careers.

After "toughness" and "rebounding," the word "depth" ranks right up there when you're playing word association with the name "Tom Izzo."  The 2009-10 team should have it (note that we haven't even mentioned Austin Thornton and Isaiah Dahlman, two players capable of being the 9th or 10th guys on a Big Ten contender).  If anything, the challenge is to fit all the depth together, balancing out the relatively experienced group of perimeter players with the less experienced cadre of post guys.

While, of course, there really isn't a magic ratio that automatically leads to Big Ten titles and postseason success, I will posit that depth is a prerequisite for success for Izzo-coached teams.  (Other coaches don't necessarily need it.)  Based on what we know right now, that prerequisite has been met.

Finally, it's worth noting that the past two seasons were the first back-to-back sub-3.00-depth-ratio years since the early Izzo-era Final Four run.  The major factors in the peaks/valleys over the 2001-2007 time frame were (1) a rash of early departures (Jason Richardson, Randolph, Marcus Taylor, Lorbek, Brandon Cotton [a VERY early departure], Shannon Brown) and (2) the bunching up of the Hill/Torbert/Anderson/Davis/Ager core playing group, all of whom departed (along with Brown) in a two-year period.  (Historical MSU roster is here.)

It would appear Tom Izzo has been able to adjust his recruiting approach to avoid an excess of early-departure guys.  The second problem is probably unavoidable as a matter of basic mathematics (Roe/Green/Lucious will depart the year after Lucas/Allen/Summers/Herzog do), but depth-ratio valleys separated by periods of 2-3 years would certainly be preferable to annual fluctuations we've seen prior to these past two years.  With a little luck, Izzo can keep the line on the chart below hovering around 3.00 for another decade (or two).