Posts Tagged ‘sports gambling’

Is there an Iron Law of 70% in sports?

December 22, 2009

Okay, if you’ve been following the writing on this blog, I’ve been running this little tally for the last week to check out how often the “stronger” teams win in NBA games (stronger defined as those with the higher listed win probability on You will know that night after night I keep noticing that the stronger team wins around 70% of the time.

I claimed this result was somehow proof of my earlier posted “luck” thesis, but now I think that’s bullshit.  But nevertheless, there’s some bizarre shit going  on here.  Everything everywhere in sports that I look at and count keeps telling me the established stronger team wins EXACTLY 70% of the time, but only 70% of the time.  Now I’m intrigued, but I have no clue what’s going on.

I need someone with mathematical knowledge to step up and explain: (1) What is it I’ve found?; (2) Is this already a well known phenomenon?; (3) What does it mean?

Here’s my evidence of this “70% law”:

First, take my NBA experiment.  Through 64 games including last night’s bizarre collapse by the Bulls, the “stronger” team has now won 45 games — 70.3%.  As I said, every night the overall tally almost always finishes right around there.

Second, I’ve been following the weekly NFL picks made on’s computerized Monte Carlo system.   If you click on the link you will notice that their overall weekly picks almost always end up right around 70% correct, and for the year even their weekly “Locks” and “ATS” picks are “locked” at 71.4%.  (That’s kind of laughable… isn’t a lock a guarantee?  Their “guaranteed” picks are no better than their overall picks!)

Third, I went back to the last two NCAA basketball tournaments and looked at the first round of picks and compared them to KenPom’s Efficiency Rankings to see how many times the stronger team won there.  The two year average: 23 out of 32 — 71.8%.  The same rate held with the ESPN “National Pool”.

Finally, for whatever reason it occurred to me to go back and look at the history of “NFL Championship Games”.  Those were the NFL’s “Super Bowls” prior to the Super Bowl, but importantly for my sake here, they were only played once on a neutral field.  The reason I added those to my survey was you presumably had two fairly even teams, with the home team being stronger simply on the basis of home field advantage (also, the home team was decided on a year-to-year basis, so that would not by itself indicate strength).

I found that in the 31 years they played the old style “NFL Championship Games” the home team won 22 times.  (Trivia:  the Green Bay Packers won two of those 9 “road championships” plus the only “neutral site” championship — so they EARNED their World Titles, baby.)   Anyway, that comes out to 70.9%.

So something is going on and someone needs to explain it to me.  But even before they do, I’ve already thought of one ramification, and it has to do with the NCAA pools next spring.

The 70% rule means even if you identify the superior team in each and every game, and especially if you are right in your identification, you will still be wrong on at least 30% of your picks.  That’s what they call a “Catch-22”.

In order to do better than 70%, you have to correctly chose which weaker teams will prevail.  But the essence of sports is a test of strength — so by definition you have to be lucky (the Catch-22 being if you start trying to pick weaker teams that could also be a kamikaze strategy because obviously if you misidentify upset games, and then also miss on the real upsets, you will end up with many less than you could have had if you picked the games straight).