Debate - World footy rankings 2008 - other countries to consider

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Debate - World footy rankings 2008 - other countries to consider

Authored by: Cam Homes
on Tuesday, March 09 2010 @ 01:15 pm ACDT

The IRB World Rankings use a 'Points Exchange' system in which sides take points off each other based on the match result. Whatever one side the gains the other side loses.
The points exchanges are based on the match result, the relative strength of each team, and the margin of victory. There is also an allowance for home advantage.
All teams start on 40 Ranking points
Points Exchanges are Doubled in World Cup Final Matches, I did same the for all IC Matches.
Margin of Victory bonus is given for wins over 15 points in IRB but I allocated the bonus for wins over 40 Points as Aussie rules matches tend to have much higher final scores than Rugby Union. You might decide that a 50 point win might be more deserving than a 40 point win.

The maximum Points exchange is limited to 2 Points. This rules out teams like New Zealand gain huge exchange points for beating India by 229 -0 in IC 08. This rules out freak results and makes sure the sytem doesn't over react.

The Home advantage adds 3 points to the Home Team prior to calculating the Rating Gap but is not added to the final exchange points ( where I stuffed up in my original calculations)

An example at how it works :- lets take Denmark and Great Britain at the end of IC02.
they were Denmark 5th with 41.60 and Great Britain 8th with 36.61 ranking points.

These teams then played one of their fairly regular internationals in July 03. in Denmark.

Denmark 41.60 + 3home adv =44.60
GB=33.61
The Rating Gap is -7.99 for Denmark and 7.99 for GB

The IRB explanation has diagrams to help work out next step but the maths is
Denmark -7.99 divide by10+1 = 0.201 Exchange Points
GB7.99 divide by10-1 = - 0.201 Exchange Points
but Denmark beat GB 12.13(85) to 4-5(29) a margin of 56 points so the margin of victory bonus comes into play. The bonus is the exchange points x 1.5.

Denmark 0.201 x 1.5 = 0.302 Final exchange points.
GB - 0.302 x 1.5 = -0.032 Final exchange points.

Denmark start 41.60 + 0.302 = 41.90 new Ranking points
GB start 36.61 - 0.302 = 36.31 new Ranking points
which still have them at 5th and 8th respectively.

Another example
Round one IC 05
Japan 12th with 32.07 ranking points(derived from several loses in Arafura Games)
Spain nil Rank but Starting with 40 Points( First International we think)

No home advantage so Rating Gap is
7.93 for Japan and - 7.93 for Spain
Japan is the lower ranked team but wins so exchange points calulation is
Japan 7.93 /10 + 1 = 1.793 exchange points
Spain -7.93 / 10 -1 = -1.793 exchange points
Japan won by more than 40 points and IC bonus double the exchange points but this puts the points over the max of 2.00
so
Japan start 32.07 + 2.00 = 34.07 still 12th
Spain start 40.00 - 2.00 = 38.07 now 8th
This is why the IRB only allows full ranking after a substantial number of games are played. We could include teams with say less than 5 matches in the ranking but as provisional only.

If you actually have a look at the "IRB World Ranking" website and then find and click on 'explanation ' and all the explanation and the reasoning on how why it is designed is there explained much better than I can hope to do.
The system is designed to produce an accurate picture of current strength, based on results. The importance of past sucesses will fade and be superseded by more recent results.

I hope the examples above helps you understanding and how I have adapted the IRB scheme.
I can be emailed at 'flinderscycles@internode.on.net' and if you can supply me with an email address I can email all of my calculations so you can see which matches I have used to get the ranking as it stands at end of 09 playing season.
Regards
Cam

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