## Wednesday, 8 August 2012

### +18 medals, but plus or minus what?

This is my last post on the Olympics: promised! My friend Stefano posted this link to an article in (one of the very few) Italian respectable newspapers (more or less the same as this, which is in English).

I took the data resulting from Goldman Sachs' analysis (usual digression and probably cheap moaning: don't these people have something far more important to do, eg stop draining money, than wasting their time playing around with this?) and plotted this.

That's the comparison between the observed number of medals won in Beijing and their prediction for the number of medals won in London. Most of the countries seem to lie on the 45 degrees line, which means that they are expected to replicate last time performance. The outstanding countries are effectively Team GB and, only marginally, Italy. The US and China are predicted to do slightly worse than last time around (a difference of just 2 medals).

1. I think the results reported are a bit confusing. In fact, the data are only given for the countries that have won some medals in Beijing and are predicted to win some in London. But in this way it is not very clear who are losing out and how much so. In the data made available, only the US (-2), China (-2) and Jamaica (-1) are predicted to have fewer medals than in Beijing. I think it would have been better to report the complete list of medal winners from Beijing in the their table.
2. I think the model gives a bit too much weight to the "home effect" (ie the increase in the number of medals due to the fact that a country is hosting the event). Team GB are doing extremely well and have already exceeded their remarkable performance of four years ago, but may be the estimation of an increase by 18 medals is a bit too optimistic. Also, it would have been interesting to see the prediction for China given all the data before Beijing to check how reasonable the "home effect" was.
3. I'm not sure why Italy are predicted to do a bit better that previously $-$ presumably that's something to do with GDP (one of the variables included in the model)? As I've mentioned somewhere else, I think that GDP is only one side of the story as it doesn't necessarily reflects investment in sports. If you can read Italian, perhaps you can have a look at this $-$ I think I agree almost entirely.
4. More importantly, both from the statistical and substantial point of view, the exercise is all about prediction (or at least the headline is). But what they have spectacularly failed to do is to report any measure whatsoever of the variability associated with their estimation. Surely their prediction will be based on reasonably different extremes, to account for uncertainty?
All in all, I think it's funny how we (I mean myself included) get sometimes carried away with this insane need of putting our day-to-day job (and supposed expertise) to use for big events, like the Euros, or the Olympics.

I asked Lizzy to declare the Olympics close on the first Sunday, when we were ahead of the game (sadly she didn't). But perhaps now it's really time she does!

#### 1 comment:

1. OK, as of Sunday morning (with only a few more medals to be given), Team GB have now reached 62 medals in total. Which means that the point estimate provided by Goldman Sachs is actually quite good. So, perhaps the "home effect" was not as overestimated as I thought.

But:
1) I still think that it would have been good to validate this (eg against China in Beijing);
2) I know that this was not a technical paper, but I think that even (perhaps more importantly!) in pieces for the general public point estimates are really not enough. What if their estimation for Team GB was 65 $\pm$ 30 medals (in which case: whatever, dudes! $-$ since they're Americans...)? But what if it was 65 $\pm$ 4 (chapeau! $-$ although they are Americans...).