Experience vs defensive (and offensive) performance - revisited

Submitted by ebv on

A few weekends ago I did some analysis that tried to answer the question: “Do good defenses need experience?”  In short, if experience is vital to a team’s performance, then we expect to see a positive correlation between a team’s experience and performance. Instead, the correlation was very weak, indicating that experience is not a major factor in defensive performance.

However, there were a number of major caveats with the approach I took, so I’ve redone some of the comparisons with the hope of addressing some of the issues.  I’ve also added the same comparison for offense.

New methodology

I’ve changed the approach to help eliminate some of the caveats to my last analysis.  Many people pointed out that players who never see the field probably skew the results.  I’m now scraping data from the depth charts on rivals.com, to eliminate that bias.  Not every team has a depth chart listed, and some were in a different format that I did not take the time to parse, but the data includes 97 teams (essentially the ones with a themed team site on rivals.)

As a bonus, rivals includes information on redshirts, which were left out of the previous analysis.  I calculate an experience score from the player’s academic year (Freshman = 1, Sophomore = 2, Junior = 3, Senior = 4, Grad Student* = 5, Redshirt = +1) so a player’s score is roughly the number of years they’ve been on the team.**  Then, because each team has a different number of players on their depth chart, I take an average.  The resulting team score has the advantage of being easily interpreted as the average number of years the players who make up a unit have been on the team (assuming they started on the team as a freshman).  I’ve split players by position, so each team will receive an offensive and defensive experience score.  Finally, I matched up the defensive and offensive FEI scores from Football Outsiders (which takes strength of schedule into account) with the experience scores and use linear regression to test for correlation.

Caveats

Of course, there are still some big caveats to this approach.  The data still does not include injuries and transfers so this may be unfairly attributing experience to teams in some cases.  The analysis also doesn’t account for talent (recruiting guru rankings) in any way.  Finally, we’re trusting Football Outsiders to provide realistic performance measurements. If their rankings aren’t accurate, none of this analysis will be either.

Results

Lets start with something new: the offense:

In the graph, each point is a team. Its offensive experience score is on the x-axis and its offensive performance score (Football Outsiders Offensive FEI) is on the y-axis.  Larger numbers are better for FEI, so good teams are at the top.  The results are almost the definition of no correlation.  Experience is not a significant predictor of offensive performance (p = 0.18) and R2 is a miserable 0.02.  We can only conclude that there is a lot more to offensive success than simply experience.

The blue lines cross on Michigan’s point.  Despite the sophomore quarterbacks, Michigan fielded one of the most experienced offenses, with over a junior’s experience on average.  Performance-wise, we’re in good shape with the second best offense in the nation. 

The maroon lines cross on Mississippi State’s point.  They have significantly less experience than Michigan, averaging ~ 2.5 years.  They’re also performing much worse; many teams with the same level of experience have better offensive output.

Moving on to defense – I’ve multiplied the football outsiders defensive FEI score by -1, so good performances are again towards the top of the graph. 

Again, the correlation is not significant (p = 0.5) and the R2 is very low (0.04).  This is actually different from the previous analysis, where we saw a significant positive correlation with a tiny effect size.***

 

Again, the blue lines cross at Michigan’s point.  Again, Michigan has one of the more experienced units, fielding over juniors on average.  Mississippi State (maroon lines) fields a lot less experience, with about 2.73 years on average.  However, despite the relative lack of experience, Mississippi State turned in a much better defensive performance this year than did Michigan.

Update - I've added a line for Michgan after the following player substitutions: Patterson for Watson (sr rs +1), Vinopal for Emillen (fr -1), and Demens for Jones (so rs +1) , removed Floyd (which I'm iffy about since he did play much of the year) (-3) and add in Avery, Christen, and Talbott (all fr +1).  The result would be just below a junior's experience: 65 / 22 ~ 2.95.  I've added the dashed, verticle line for that experience level.  If you want to check my math, I posted the raw data for Michigan in the comments.

One final note – the pattern of elite units (either offense or defense) having middling experience holds for both sides of the ball, i.e. the top right of both graphs is empty.  The NFL draft is probably the simplest explanation for this.

Conclusions

I am surprised by the nearly complete lack of correlation in the data.

Is it possible that we need more variables to make sense of this data?  (Any stat experts know whether you can underestimate an effect by having too few variables?)  It’s also possible that an interaction between several variables might provide a good explanation for our data; for example we might need experience, NFL-worthy talent and great coaching to produce an elite defense, but none of the three alone will do it.

Speaking of talent, yes, that information is not included here, and probably should be.  However, we aren’t looking for a perfect correlation.  If experience accounts for a significant fraction of a team’s performance, we ought to see some kind of correlation, even a weak one, with an R2 that indicates experience explains some portion of the variation in the performance variable.  Instead, there’s almost no correlation at all. This really makes it look like performance comes down to coaching and recruiting, and not so much experience, at least in terms of years on the team.

An alternate explanation, put forward by MCalibur in the comments on my last post, is that the concentration of experience on the field is more important than simply gross experience. Perhaps coaches can hide some freshman mistakes behind solid play from battle-hardened seniors. Michigan’s true-freshman filled secondary might leave the coaches with no place to hide their players inexperience. If I continue to pursue this, I’ll try breaking experience down by position.

Update 2  On Steve Sharik's suggestion I repeated the comparison with the median. It cleans things up a little bit, but there still isn't good correltion.

* Don’t worry, there are no redshirt grad students, I checked.

** I got a number of excellent suggestions from bighouseinmate, MCalibur, expatriate, tpilews and probably others, that a more relevant measure of experience would be years as a starter as opposed to years on the team.  I agree completely.  Unfortunately, that information is not consistently available, so I’m sticking with academic year as a proxy for that until I can find a reliable source for that data.

*** Perhaps most surprisingly, we now see a negative (!) correlation between defensive performance and experience, which, if it were significant, would mean that as your team gains experience it turns out worse performances.  However, these results are so close to random, the sign of the correlation should probably be ignored.

Comments

AC1997

December 15th, 2010 at 12:49 AM ^

How can you say that Michigan has the most experienced units on either side of the ball?  Averaging over a junior status?  What depth chart are you looking at? 

Starting Defense:

  • Roh - Soph
  • Martin - Junior
  • RVB - Junior
  • Gordon - R-Freshman
  • Demens - Soph
  • Mouton - Senior
  • Rogers - Senior
  • Avery - Freshman
  • Kovacs - R-Sophomore
  • Vinopal - Freshman

Unless you're counting bench players or guys who we thought were starting (Woolfolk, Floyd, Banks, Ezeh) then something's broken.

Offense is a little closer because of two seniors on the line and some junior WR, but still surprised at the result.

MGoTarHeel

December 15th, 2010 at 1:05 AM ^

If you count redshirts as their listed year and assign each player a "score" for their year (ie. Roh=2, Gordon=1, etc), then they average out to 2.3, or just older than a sophomore. Counting redshirts as their actual age will yield an average of 2.5.

This is flawed anyway, as age does not really correlate to "experience" as much as on-field action does. The seniors on our roster aren't there because they have been starting for four years and have a wealth of experience and talent, they're starting because of injuries/attrition/lack of recruiting above them and in spite of the fact that they were not good enough to break into the starting lineup at any previous point in their careers.

ebv

December 15th, 2010 at 9:38 AM ^

Here's what the data for Michigan looks like with my score in parentheses:

ryan van bergen     jr.     rs  (3 + 1)
renaldo sagesse     sr.    (4)
greg banks     sr.     rs    (4 + 1)
steve watson     jr.     rs    (3 + 1)
mike martin     jr.     (3)
william campbell     so.    (2)
craig roh     so.    (2)
j.b. fitzgerald     jr.    (3)
thomas gordon     fr.     rs  (2)
kevin leach     jr.     rs    (4)
obi ezeh     sr.     rs    (5)
mark moundros     sr.     rs    (5)
jonas mouton     sr.     rs    (5)
mike jones     so.    (2)
james rogers     sr.    (4)
j.t. floyd     so.     rs    (3)
jordan kovacs     so.     rs    (3)
cameron gordon     fr.     rs    (2)
vladimir emillen     so.    (2)

4+4+5+4+3+2+2+3+2+4+5+5+5+2+4+3+3+2+2 = 64 / 19 ~ 3.37

This is a pretty accurate two-deep at the beginning of the year.  In a perfect world, this data would include transfers and injuries already, but since it doesn't we can try to correct for it.  Watson should probably be replaced with Patterson (sr rs +1), Emillen with Vinopal (fr -1), and Jones with Demens (so rs +1).  We'd get 65 / 19 ~ 3.42.

Ok, so lets go crazy and remove Floyd (which I'm iffy about since he did play much of the year) (-3) and add in Avery, Christen, and Talbott (all fr +1).  This gets us below a junior's experience: 65 / 22 ~ 2.95.

I've updated the graph with a second vertical line showing Michigan with injuries / transfers / freshman.

DreadPower

December 15th, 2010 at 9:50 AM ^

Moundros (5)

Rogers (4)

Does this really represent their "experience" on defense?

And why do you have backups listed for every position except the ones in the secondary, our most inexperienced area?

It seems like you are trying to make our defense appear way more experienced than it truly is.

Painter Smurf

December 15th, 2010 at 1:19 PM ^

A lot of the experienced players from the calculation are walkons or position switchers who moved over from offense mainly to add depth on a very lean defense.  So it would assign the same weight to a guy like Banks, who is an experienced DL all the way, and a guy like Watson, who is not a legit upperclass DL and is only playing there due to the numbers problem.  It would be tough to take factors like these into account.

TrueBlue2003

December 16th, 2010 at 1:34 PM ^

Experience is overrated.  Even though Mouton and Ezeh and several of the D seniors actually have been starting and playing for a long time, that experience hasn't helped them.  They just aren't great players and more years haven't helped them.  How frustrated have we been the last couple years that these guys didn't get better?  You need good players and talent to be a good unit and until we get that on defense, we aren't going to be very good.  We can't just expect all the current guys to figure it out next year.  Great analysis by the OP.

steve sharik

December 15th, 2010 at 2:07 AM ^

Perhaps you should use median experience instead of average.  For example, a defense with 5 5th year seniors and 6 true freshman yields an average experience of 31/11 or 2.8181....  That's a shade under a junior average, but I think we all can agree that the example is not an experienced unit (nor is Michigan).

On the other hand, the example defense's median experience is 1.0, or true freshman, which is how I'd expect such a unit to perform.

It would be interesting to see how the numbers play out. 

WhetteFahrtz

December 15th, 2010 at 3:23 AM ^

I just finished an Econometrics course and left feeling as if I didn't learn anything but amazingly I understand all of this.  Could you post a more detailed explaination of how you arrived at this, e.i; the variables used, your regression equation, the statistical program and the AOV.

Something to add that might create a more accurate result for the offense would be to include the  combined offensive starts for the O-line.  I've seen data that looks at just the O-line starts and it's fairly coorelated to how well a team does.  Usually teams with over 60 combined starts have .500 or better records, and > 80 starts = around a 9 win season. 

*also I've been amazed at how detailed and awesome the people on this site are when it comes to football, being this, or the guy who has been breaking down all of our game film.  Fascinating stuff.

SFBayAreaBlue

December 15th, 2010 at 4:52 AM ^

I'd like to see your data weighted by star rankings of the players or some other method.  The idea being that if you've got a lot of 5th year 1 stars and walkon's, you're still not going to be very good, but a team with a handful of 5 star redshirt frehsmen and a couple seniors should do okay. 

Maybe you could color code the groups by conference or something. 

In other words, the effect of experience is probably real, but unmeasurable by your current method because other factors have a bigger influence.  You need to normalize the data somehow, and isolate the variable of interest.

LB

December 15th, 2010 at 7:52 AM ^

has to be meaningful at some point, I wonder if games started would yield better results. I would think those stats would be available, and it shows actual game experience, vs, for example, a 5th year senior whose leadership and efforts can't be questioned, but who might lack the size, speed or talent to earn a starting spot. It might even account for the true 5 star talents and the Lewans of the world.

TrueBlue2003

December 16th, 2010 at 1:21 PM ^

This is great work.  One could argue that years in the program is more relevant than years starting and that your analysis of experience is best.  I'm not sure why people on here say years in the program only means more years of lifting weights.  RR has said many times that improvement is made in spring ball and camp and practice when he warns that in-season improvement is minimal.  Learning in practice, being coached and working on S&C does much more to improve a player than playing for 20-30 minutes on Saturdays.  Look at Denard.  It was the off-season experience last year that made a difference for him.

It would be interesting to see a regression with experience and GURU ratings as the independent variables.  Would probably just prove that talent is immensely more important than experience.

BlueLaw

December 15th, 2010 at 10:16 AM ^

It would be interesting to see the difference between starters and and the 2 deeps.  It could be that a lot of experience (or age, I suppose, in this analysis) on a starting defense would lead to different results. 

rcm

December 15th, 2010 at 10:45 AM ^

 

...ish

I know it would probably be a complete pain in the ass to do so (easier said than done, etc.), but you said that you wanted to add more variables.  What I'd suggest is the addition of metrics that can be applied across every team you've included.

I'm envisioning this detailed of an analysis coming to fruition in a third dimension of sorts.  For example, in your defensive graph, leave the x- and y- axes as is, but add a z-axis that tallies pass break-ups, interceptions, sacks, tackles, tfls, etc for each defense.  There might be a correlation that develops that sees the outlying defenses along the top of the y-axis and further in the x-direction separate themselves from the teams that lie closer to the lower-left portion of the graph.  Better yet: in order to further highlight experience (that being starts), look back at players' performances from past years, and add those as well.

Thinking out loud, etc.  You are right though, there should be a trend somewhere or another, or else why would we see any reason to use this kind of statement as a topic to research.

CompleteLunacy

December 15th, 2010 at 11:33 AM ^

Don't kid yourself, you did a nice analysis here...just because the numbers don't show anything doesn't mean we can't glean anything meaningful out of them. You're probably right, there are many variables to this that would change the analysis one way or another...what we do know is based on average/median years alone, there is no correlation. 

Others above have supported adding more or different variables, like games played rather than years. Or maybe a measure of "experience" worth trying is the ratio of  seniors to freshman on the field, as I would argue those two years are the most significant in determining experience or a lack thereof...or perhaps ratio of upperclassmen to lowerclassmen would be a better all-around variable for "experience". And maybe the inclusion of GURU star rankings as a factor in the analysis would yield more significant correlation (as we can surmise that having experienced 3-4 star players is usually way better than an experienced 2 star player)

Whether you delve deeper or not, thank you for the graphs and data and such. The stats nerd in me really wants to see this taken another step further, and there's quite a few possibilities with which to do it.

Ziff72

December 15th, 2010 at 12:01 PM ^

Players more often than not are better than the previous year.  I don't need a graph to tell me that defenses are better when more experienced.  They are.  End of story.

I think if you wanted to get a meaningful analysis.   Add up the amount of starts each player has had in their career.  Then get back to me.

Obviously Michigan was an outlier this year interms of stats.   What are the odds of having that many seniors on your defense that can't or didn't play.

Moundros, Ezeh, Rogers, Banks etc... 

BleedingBlue

December 15th, 2010 at 12:29 PM ^

You need to use a combination of career starts plus age to get a true "experience" factor that makes sense.  And you should not use the whole 2-deep.  Only the starting lineup, or maybe Starting lineup plus the 2 or 3 players that play more than 33% of the snaps on each side of the ball.  

There are tons of information sources out there aside from Rivals.

Mgoblue.com has TONS of info for one and espn.com for another.  

Blue in Seattle

December 15th, 2010 at 1:24 PM ^

I have two viewpoints.

The first is that your definition of experience is really only describing how much opportunity the players had to go to the weight room at a University Level.  While this is important, I think it's also very common for all teams to require their players to lift weights.  There could be variations in quality of S&C, but that likely is strongly correlated to the coaching performance rather than just age.

Second, I was thinking that you are trying to show the correlation of experience to results, and to do that you need to isolate the talent variable.  If you weight the experience with a talent score as some have suggested, then I think all you'll do is prove that the most talented AND experienced teams have the best results on the field.  To which I say, "Duh".

Unfortunately to isolate, the only thing I can think of is that you have to look at all the teams in detail and put them into groupings based on their talent score, and then you can compare them across the variable of age or experience.

In the end, I think you are doomed.  This is impossible to prove because of the complexity of talent and experience and coaching.  Also Football is the most complex team sport, with 11 players on each side.

I remember when the Fab Five were at the Finals for the second time.  A friend of mine was a long time Tar Heels fan.  His opinion on Michigan was that they couldn't defeat North Carolina because they did not play as a team.  He thought Steve Fisher was an excellent recruiter (and of course in a few years we found out why), but was not a talented coach at all, and hadn't really done anything to develop the players.

In general I agreed, Michigan's performance frequently looked more like street ball than a college basketball game.  YET, that team of Five made it to the Finals twice before ever becoming upper classman.

Back to football, look at OSU, many times in the NC game, but many times coming out with a loss.  I don't think anyone would disagree that they clearly have the best talent pool of players in the Big Ten, they also pretty consistently put players on the field who have started for 2 years or more.

Now is that just because their players are older? no.  Is there talent pool proof of anything other than the ability of the coaches, maybe, recruiting is a different skill than teaching/coaching. But most of all if you try to analyze based on how many starts players have, then you are just going to prove that teams that find the best talent, and keep the talent pipeline flowing so they are always fielding a team of Juniors and Seniors, win the most games.

What you want to prove is that there is a team with incredible talent, who's coach has lead them to disaster this year (cough, Texas, cough) and see what you find.  Yes anecdotal instead of statistically cool, but such is the way with complex systems of too many variable.

 

SmithersJoe

December 15th, 2010 at 2:01 PM ^

We need to be careful about reading too much into the relative lack of correlation here.  All this says is that there appears to be no significant correlation between the 2 specific variables you have selected.  The failure to confirm this specific alternative hypothesis does not mean you have failed to reject the null hypothesis.

Alternative hypothesis: there is a significant correlation between average years of experience on a team's depth chart and its defensive FEI score. False.

Null hypothesis: there is no correlation between experience and performance on defense.  May still be rejected by confirming a different alternative hypothesis.

steve sharik

December 15th, 2010 at 6:46 PM ^

SE: VanBergen = 3 (3rd year getting PT)

N: Martin = 3

WE: Banks = 2

Sam: Roh = 2

Mike: Demens = 2

Will: Mouton = 4

Spur: C. Johnson or T. Gordon = 1

Bandit: Kovacs = 2

SC: Floyd = 2

WC: Rogers = 1

FS: C. Gordon or Vinopal = 1

Put the data in an ordered list and we get:

1, 1, 1, 2, 2, 2, 2, 2, 3, 3, 4

mean = 2.09

median = 2

mode = 2

Any way you statistically look at it, it is a 2nd year defense in a somewhat new defensive scheme with new terminology.  Gee, why were we so bad?

beenplumb

December 16th, 2010 at 9:39 AM ^

Adding more variables to your model could help to explain more of the variance and improve your r-squared. Also, there could be confounding variables you're not considering. Years starting would be one I would look at right away. Also, if it were at all possible to consider their recruiting rating I would look at that, too (it might very well turn out that that isn't a useful predictor, but you never know until you try :) ).

And, as always with regression (and really most other parametric analyses), increasing sample size will almost always improve your p-value.

Overall, neat analysis. Definitely a lot of work put into this, and I applaud that.

Born Blue

December 16th, 2010 at 10:41 PM ^

I love and appreciate your very fine work on these statistics, but I also think it's time to face a very important non statistical factor...some of these teams are horrible, some of these teams are excellent...and experieince doesn't always tell the tell!   From personal experience, one of the worst teams I ever coached was senior laden.  Workouts, level of competition, committment level on the part of the coaching staff or the athletes was never in doubt, it was always there, always evident, but, the team just, well...sucked!   one of the best teams i ever coached was led by several freshmen!  Same workouts, same strong work ethic, same coaching staff...never could explain it!  Coach of the year in one case, and bum the other.  Just happens.

Honestly, we B10 fans should know this!  Weren't there yrs when some teams in the league just plain sucked! Didn't matter how many years of experience they had, they just sucked and routinely got beat down weekly.  You can argue they didn't have the same talent level as more elite teams, and their would be some truth to that, but I have also lived in talent rich FL, and watched many talent heavy squads mired in mediocrity...it just happens.

This I DO believe, our kids have talent, heart, committment, and are driven, so, in spite of youth, inexperience, or whatever else we might prognosticate about, they shall W-I-L-L themselves to better performances in the future, why?  Simple, they have talent, and experience, and a desire to obtain better/greater results, not for us the fans, the school or even prestige, they will do it because it's what they want for themselves.

Crystal ball aside, time will tell. Thanks for listening, keep up the good work!