Among the college hoops media, teams only seem to be as good or bad as their last couple games. (And, ironically, as I proofread this, Boston College shocks Syracuse.) Even fans paying close attention don’t tend to look much further in the past than the last AP top 20 ratings—at least until Selection Sunday.
If you think the balance of power in college basketball changes a lot from one week to the next, however, you might be surprised at how it shakes up over the course of three weeks. I sure was last night when I stumbled across an Excel sheet from January 28 ranking the KenPom top 20. It made me wonder about two things:
- How have the efficiency numbers for today’s top 20 changed over the course of three weeks?
- What has happened to the individual teams that made up the top 20 on January 28?
Let’s answer the first question. Take a look at the chart below. The orange line represents the Pythag values of the 20 most efficient from three weeks ago. The red line represents today’s KenPom top 20—and the schools along the bottom occupy those 20 slots.
The first thing that jumps out is how much the overall efficiency of the nation’s best teams has dropped in just 22 days. Every single position is a notch lower—and teams ranked 12th through 20th are considerably lower than their past counterparts. Moreover, the second best team of January 28, Creighton, was playing more efficiently than the best team, Arizona, is today. In fact, on January 28, you had 15 teams, ranked from second to 16th, who were bunched together in the efficiency gap between today’s top 11 schools.
Let me put that another way. Three weeks ago, there wasn’t a sizeable drop off in team quality until the 16th ranked team. Today, the quality drops off at the 12th team. And, oh, by the way, the overall quality of the top teams has generally declined.
(NOTE: If I compared the quality curve of today’s KenPom top 20 to past years, as I’ve done in previous blogposts, these numbers would look shockingly low. And I would therefore conclude that we’re in for a crazy 2014 tourney, since there’s a positive correlation between the relative strength of the top 20 and the chalkiness of bracket outcomes. However, you’ll notice I’ve stopped doing those comparisons. The reason is that this year’s KenPom numbers are derived using a different formula than previous years. Ken acknowledged that he’s removed the bias of mismatches from his efficiency ratings—and that’s driven overall values lower. So the old pre-tourney Pythag values I’ve provided aren’t exactly comparable to this season’s Pythag numbers. There’s no way around it: we’re dealing with apples and, well, slightly different apples. The bottom line: it’s difficult to say whether this years best teams are weaker than their historical counterparts or not. Throw in the impact of the new offensive-friendly rules on efficiency numbers…and we’re essentially in uncharted statistical territory.)
As surprised as I was to see how the KenPom top 20 had sagged in terms of efficiency over the last three weeks, I was even more stunned to see how the quality of those individual teams had changed since January 28. Check out this next chart. The orange line represents the Pythag values of the AP Top 20 from three weeks ago. And those old efficiency leaders are listed along the bottom. The red line represents what their Pythag value is today.
Look at how dramatically the efficiency values of the erstwhile top 20 has changed:
- Some teams, like Louisville, Virginia, Villanova and Kentucky, have seen virtually no change in their overall efficiency.
- Other teams, like Arizona, Creighton, Syracuse, Wichita State and Kansas, have only seen a small degradation in their efficiency.
- Another group has suffered a more significant drop-off, including Iowa, Wisconsin, Michigan and Ohio State (Hey, those are all Big Ten teams!)
- And then there are the major decliners: Michigan State, Pittsburgh Oklahoma State (yikes!), Florida State (yikes! part two) and Iowa State.
- Finally, you have Florida and Duke, the only two teams who’ve made substantial improvements in their overall efficiency
I have three takeaways from this analysis:
- A lot can change in the quality of a team over the course of five or six games.
- By downplaying mismatches in his new algorithm, KenPom’s Pythag values are based on less data and thus prone to wider swings. Ken admits as much. That’s at least part of the reason that the fate of some teams have changed so drastically in three weeks.
- There are 25 days until Selection Sunday. Today’s KenPom top 20 are liable to see a similar range of changes in their quality between now and then.