Monday, January 2, 2012

Any Statistics Guys Out There?

I apologize in advance for the rare non-gaming post and assure you it will not be a frequent occurence.  But I have a question for any statisticians out there.  Here goes.

Every week, I choose 10-15 professional football games to predict.  What I do is select who I think will cover the established gambling point spread.  So I don't pick winners or losers.  I try to pick who will cover the spread.  In theory, this should be a 50% proposition.  So if I was a trained monkey randomly picking which team will cover the spread, I should get about 50% of the games right.  In fact, Las Vegas sets the spreads so that approximately 50% of the money gets placed on each team.

Well, the season is over and my picking record is 119 wins and 83 losses over the course of 202 games.  That is, I correctly predicted which team would cover the point spread 59% of the time.  I was thrilled with the result and bragged to my brother about it.  I told him that most NFL analysts on TV don't pick point spread winners correctly 59% of the time.

But Dominic (my brother) rained on my parade by saying his gut instinct told him it was not a statistically meaningful sample since I only predicted 202 games.  I told him I thought that was enough games to draw some inferences about my handicapping ability!  I said "Dom, if I was to flip a coin 202 times I doubt it would come up on a particular side 59% of the time."

So does anyone know if 202 games is enough to draw a meaningful conclusion about my ability to pick games?  Or could it be pure luck?  I promise my feelings won't be hurt!

PS: I didn't actually bet a single penny.  I'm not really a gambler.  This was all to see how well I could do at picking point spread winners.


  1. I'm not a statistics guy, but from what I understand of the laws of probability, you'd need more samples (such as comparing how you do over the next two or three seasons or so) to see if you've got some skill influencing the results as you believe, or it was just a chance occurrence as your brother believes.

  2. Excellent - thanks! Just for the record, I don't think I have any skill in influencing the results, but I hope I have some skill in predicting the results. :)