This post will examine the accuracy of the KenPom rankings and predictions, and try to evaluate the performance of Michigan's basketball season in comparison.

I've been following along with Brian/Tim's basketball previews and was wondering how accurate the KenPom predictions have been.  I'll graph the predictions versus the outcomes, and try to adjust the predictions based on the current rankings (versus rankings at the time).  I will also include a "baseline" program for analysis and comparison to our manic/depressive performance this season.

Numbers:
Michigan is currently ranked 85/47offensively/defensively according to KenPom.  Compare that to the competition:

team	current offense rank	current defense rank
minnesota	38	53
osu	10	19
ill	67	40
psu	73	113
iowa	141	162
minnesota	38	53
wisc	11	15
nw	27	163
iowa	141	162
msu	28	31
purdue	33	5
wisc	11	15
uconn	66	28

And prediction/results for those games:

team	kenpom prediction	actual difference	kenpom - actual
minnesota	2	-16	18
osu	12	11	1
ill	1	6	-5
psu	-8	4	-12
iowa	-3	-2	-1
minnesota	9	-7	16
wisc	5	8	-3
nw	3	13	-10
iowa	-11	-14	3
msu	3	1	2
purdue	11	10	1
wisc	-9	16	-25
uconn	-1	-5	4

Simple numerical average of (kenpom - actual) gives -0.85, which shows pretty good prediction value.

Showing the results graphically:

The orange line shows how close the kenpom prediction was at the time.

Now, we will look at the current rankings to try to get a better feel for the prediction value.  Assuming that a better team will beat a worse team, we will estimate margin of victory based on relative ranking.

team	rank average	michigan rank - team rank	ranking difference prediction
minnesota	45.5	20.5	2.05
osu	14.5	51.5	5.15
ill	53.5	12.5	1.25
psu	93	-27	-2.7
iowa	151.5	-85.5	-8.55
minnesota	45.5	20.5	2.05
wisc	13	53	5.3
nw	95	-29	-2.9
iowa	151.5	-85.5	-8.55
msu	29.5	36.5	3.65
purdue	19	47	4.7
wisc	13	53	5.3
uconn	47	19	1.9

The last column is expected margin of victory, if the teams played today.  Graphing the RDP versus actual gives this:

The games with big gaps would be upsets, but overall the prediction percentage is .61, that is, the percentage of games that the current rankings would predict correctly, win or lose.

Now let's compare that chart to a control, Michigan State. MSU's rank is 28/31.  The data in question:

team	actual difference	ranking difference prediction
osu	7	1.5
ind	-14	-14.65
psu	-12	-6.35
purdue	8	1.05
ill	5	-2.4
wisc	14	1.65
nw	-9	-6.55
mich	-1	-3.65
minn	-2	-1.6
iowa	-7	-12.2
ill	-10	-2.4
minn	-13	-1.6
iowa	-18	-12.2

and chart:
Now the prediction rate is .92 (12/13).

So what does all this show?  I think it shows the value of KenPom's system when used on a good team.  Or, conversely, the inconsistency of Michigan this season - beating teams they shouldn't beat, losing to teams they should beat.  I'm not a gambler, so I didn't take into account the value of covering against the spread, I'm simply looking at this as a fan and judging based on wins/losses.  As far as wins and losses, this system seems very accurate.  I may look into tweaking the ranking calculation to better match the results, but I think the basic idea is pretty solid.