Sunday, November 25, 2007

Maradona and Statto

I usually play football twice per week. One of those games involves a group of us who have been playing at the same time each week for nearly a decade. The sides vary, but we have records of the match results, and also on how often each player wins. But in today's lesson on how stats can mislead, a reminder that win ratio does not correlate to talent or ability.

It should be obvious, but to help understand why, assume that one player (for the sake of argument let's call him X) is much better than everyone else. Fair enough, X would be expected to have a decent win ratio. But look at the effect on everyone else.

When we are choosing sides before the games, we make a conscious decision to balance them. And if we have said that X should expect a high win ratio, then those players who are almost as good will naturally have a correspondingly low win ratio. Yet we have just implied that they are amongst the best players that we have!

Common sense? Or just an excuse for poor results?


Anonymous said...

Rana, if I follow your logic through the stats are meaningless. If eg Deano is more often on the winning team then the weighting wasn't enough.
I'll try and get along to 'ricy tomoz as I am in the area until cob-factor my dynamite skills into your spreadsheet.

RNB said...

Yes indeed, in this case the footie stats are basically useless in terms of predictive power!

But of course that is not the case for the more serious stuff that we do with campaign and sales ratios ;)

Anonymous said...

thinking on;

The team selection is not based on your stats but it is based on your opinion of the players ability.

If the game is always a draw then you are a good judge of someones footballing ability.

Your stats are merely a record of that. If you pick the team based on the stats you are proving that your opinion is incorrect. I guess you can learn from your failure to pick a team that produces a draw- over a decade you say.......