This ICC team ranking business

Srinivas Bhogle explores the pros and cons of the ICC rankings system.

“What’s India’s current ranking in ICC’s Reliance Mobile ODI Championship?”

“At the moment, India is second with 124 points.”

“But, wait a minute … wasn’t India first a little while ago, and then wasn’t it third too a little while ago?”

“Yes, India was indeed first and third very recently. And did I hear you say ‘Jack Robinson’? If yes, India must now be second!”

So what’s going on? It really has to do with the way the ICC rankings are defined, as we shall soon see.

Let us look at the current rating of Australia (128), India (124) and South Africa (121). This rating is computed by dividing the team’s total points by its total matches (see table below).

Now suppose India wins the first match in its forthcoming 7-match home series against Australia.

Because India beat Australia, it wins Australia’s rating (128) plus 50 points. So India gets 128+50 = 178 points.

Because Australia lost to India it wins India’s rating (124) minus 50 points. So Australia gets 124-50 = 74 points.

If we now do the arithmetic, India’s new rating is now (3852 + 178)/(31+1) = 4030/32 = 126 (125.94) and Australia’s new rating becomes (4234 + 74)/(33+1) = 4308/34 =  127 (126.71).

So just one point (actually 0.77 points) now separates the two teams.

If India also wins the second match, it will again be No. 1 with a rating of 127 (127.48), 2 points above Australia’s 125 (125.26).

We expect the series to be close … so expect the ICC rankings to go up and down like a see-saw, and expect Ponting and Dhoni’s teams to keep exchanging the top crown after every other match.

This happens because the ICC rating formula – admirable in many ways – has a worrying middling propensity.

We’ll end off with a final Q&A:

“I presume that Australia is now the ICC ODI champion because it won the Champions Trophy?”

“Not really … it’s more because Australia defeated England 6-1 in a ridiculously listless ODI series!”

The cutting edge with numbers: The ICC ODI ranking’s middling propensity

If we see the progress of the ICC ODI Ranking Championship (plotted on the y-axis) during the first 9 months of 2009 (1=Jan, 2=Feb … 9=Sep), we see that the three rating worms keep getting entangled with one another.

Australia’s steep climb is only partly due to its victory in the final of the Champion Trophy; the real reason is the 6-1 England whitewash. Notice therefore that the rating does NOT give greater weight to ‘big’ matches.

Interpretation: The ICC rating scheme has two weaknesses. It tends to cluster teams with similar performances into a tight embrace and fails to adequately reward wins in the big ODI contests.

The scheme is otherwise elegant; especially in the way it builds in the opposition’s strength and progressively reduces weights for older matches.