T20 Ratings - World Cup Edition (final)
Russell Degnan

Rankings at 16th June 2009			form
1.	Sri Lanka	1332.37	+103.40
2.	South Africa	1320.12	+31.17
4.	Pakistan	1279.52	+37.51
6.	West Indies	1190.47	+37.30

Prediction for the final
Pakistan v Sri Lanka 5 runs

Sri Lanka's annihilation of the West Indies (and most everybody else) has put them to the top of the ratings going into the final. Their probability of victory comes to 58%.

A word too on form, and perhaps a question. The main purpose of the form variable is to smooth out the volatility of unexpected results, by "banking" them, such that the effect of that result will not carry over until later games. If a team consistently loses worse than expected their rating will shift more quickly to its new equilibrium. On the other hand, if the loss was unusual, the rating will stay relatively stable.

Which brings up a question, possibly philosophical: is form an indicator of where the rating will go, and therefore should be added to make predictions; or where the rating has been, and therefore should be deducted because that is where it may return? In other words, is form a meaningful number, worth reporting, and in what sense? If results were completely random, then a run of bad form would dip the rating more than necessary, which oddly enough will actually increase volatility (sort of like irrational exuberance in a stock market). Conversely, the relative form of the West Indies and England prior to their Carribean match-up indicated that the series would be closer than the ratings might indicate; similarly Australia's form in test cricket began to dip markedly even before their horrid run against India and South Africa.

The reason for asking this relates to Sri Lanka's current form, currently over 100. Partly, their form indicates only that they are winning. The expected margin against other top-8 sides are so narrow that almost all wins beat the margin by a lot. Similarly, South Africa were equally dominant leading into their semi-final against Pakistan. The numbers are inconclusive to date, but anyone looking for an extra reason to lean one way or the other may like to consider the implications of strong form on their expectations.

Idle Summers 20th June, 2009 13:08:57   [#] [2 comments] 

T20 Ratings - World Cup Edition (semi-finals)
Russell Degnan

Rankings at 16th June 2009			form
1.	South Africa	1332.38	+74.26
2.	Sri Lanka	1287.12	+51.58
4.	Pakistan	1262.73	+15.68
5.	India	1242.87	-56.02
6.	West Indies	1222.07	+34.53
7.	England	1171.75	-43.13
8.	New Zealand	1166.49	-71.48
11.	Ireland	783.19	+49.78

Predictions for semi-finals
Pakistan v South Africa 7 runs
West Indies v Sri Lanka 7 runs

South Africa and Sri Lanka have emerged as the clear favourites for their respective finals, having cruised into the semi-finals undefeated, and in outstanding form. However, neither side has a greater than 60% chance of victory, so keep tossing those coins.

Idle Summers 17th June, 2009 13:49:59   [#] [3 comments] 

Monday Melbourne: CLXXVI, June 2009
Russell Degnan

Princes Bridge, looking out. Taken June 2009

Melbourne Town 15th June, 2009 12:44:29   [#] [0 comments] 

T20 Ratings - World Cup Edition (match day 6)
Russell Degnan

Rankings at 14th June 2009			form
1.	South Africa	1306.64	+91.15
3.	Pakistan	1271.67	+44.75
4.	India	1262.85	-64.27
5.	Sri Lanka	1254.14	-19.15
6.	West Indies	1206.92	+16.91
7.	New Zealand	1198.87	+26.82
8.	England	1190.50	-22.51
11.	Ireland	763.67	+43.03

Predictions for match day 6
Ireland v Pakistan 51 runs
England v West Indies 8 runs
New Zealand v Sri Lanka 6 runs
India v South Africa 4 runs

As noted the day before yesterday, I took a moment to compare predictions, based on both the current rating, and current rating with form. The short answer: neither are much help. The average error in both was almost exactly 28 runs; by comparison, the average error if a tie had been predicted for every match: 24.6 runs. Looking at the scatter-plot of results, it is possible that it will converge on a predicted margin half what it currently is, with a standard deviation of 20 runs. In other words, a massive 400 point difference in rating points is needed before the win percentage approaches 65%.

On a different note, Sri Lanka's travails against Ireland has meant their game against New Zealand is now a must-win to go through, whereas the South Africa v India game is marked as "dead", in case India annihilates South Africa and still receives little gain in the ratings.

Idle Summers 15th June, 2009 12:02:33   [#] [0 comments]