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Sunday, October 23, 2022

Is there a regional bias in the elo rating ?

An interesting question popped up in the discussions around my World Cup simulations and more specific the somewhat lower than expected predicted performance of Senegal compared to home nation Qatar in group A. 


Amir commented:

"Elo indeed has a regional problem - since there are not many matches between teams from different confederations, it takes a long time for ELO to adjust to the actual average per confederation.

If the difference are getting smaller (which is something worth testing), it means that Elo will indeed under-estimate CAF."


Apart from the difficulty to determine the "actual average per confederation", I personally have the impression that elo ratings are not regionally biased, because there isn't anything in the elo calculation that's influenced by the team's confederation. But maybe, indeed the number of intraconfederational versus interconfederational matches a team playes could be the exogenous factor. I decided to give it a go and research this.


First I will describe the features of the elo rating calculation:

  • elo-ratings of both teams in a match are adjusted according to the difference in elo-ratings between both teams before the match with the home team, having home field advantage, receiving an extra 100 rating points. The rating points one team wins are lost by the other in all circumstances: it is a zero-sum system with a constant number of points in the system, unless a completely new team is introduced to the ranking;
  • in case a new team is introduced in the system a starting points number is estimated for the team. Within some 30 matches the points total for the new team is finetuned against the points of their opponents in those matches and their points total will, from that point on, reflect their 'true' strength;
  • every match of the National Team of each country counts, at least: to the discretion of the maintainer of the elo-system. For instance the matches in the African Nations Championships where countries are only allowed to select players from their own domestic league, are excluded. On the other hand, matches of Senegal in the last COSAFA Cup, where they played as a guest without their European-based stars, were included;
  • 5 different types of matches with corresponding weights are applied:
    • 60 - World Cup finals (WC);
    • 50 - continental championship finals (EURO, Copa America, Gold Cup and the Nations Cups of AFC. CAF and OFC) and major intercontinental tournaments (the former Confederations Cup);
    • 40 - WC and continental qualifiers and major tournaments like f.i. the Arab Cup, COSAFA Cup, the regional championships in Asia (East, South-East, South, West), Gulf Cup etc.;
    • 30 - all other tournaments;
    • 20 - friendly matches;
  • also the goal difference in a match has an effect on the exchanged rating points;
  • see http://www.eloratings.net/about for all the details.


I selected from my match database all matches played since January 1st 1980 which are included in the elo rating calculation and determined the match type and confederation of each participating team. There were in that time frame three confederation changes:

  • Israel switched per 1/1/1994 from AFC to UEFA;
  • Kazakhstan switched per 1/1/2002 from AFC to UEFA;
  • Australia switched per 1/1/2006 from OFC to AFC.


The distribution over the match types in this sample:

type

N

perc

60

592

2%

50

2.242

7%

40

16.697

50%

30

3.005

9%

20

10.952

33%

total

33.488



Here are tables with the intraconfederational (own confed) versus interconfederational (other confed) matches per confederation and match type. Note that per confederation the matches are counted with at least one team from that confederation involved. This means that the line with the totals shows not the summed number of matches per confederation against other confederations but only half of it:


All matches

against

confed

own confed

other confed

own confed

other confed

current number of member NT's

AFC

6.177

2.197

74%

26%

46

CAF

7.731

1.430

84%

16%

54

CONCACAF

3.863

1.667

70%

30%

35

CONMEBOL

1.426

1.844

44%

56%

10

OFC

714

401

64%

36%

11

UEFA

8.483

2.649

76%

24%

55

total matches

28.394

5.094

85%

15%

K=60: WC finals

against

confed

own confed

other confed

own confed

other confed

AFC

1

107

1%

99%

CAF

0

132

0%

100%

CONCACAF

1

99

1%

99%

CONMEBOL

8

193

4%

96%

OFC

0

6

0%

100%

UEFA

144

339

30%

70%

total matches

154

438

26%

74%

K=50: continental championship finals and major intercontinental tournaments

against

confed

own confed

other confed

own confed

other confed

AFC

319

61

84%

16%

CAF

618

40

94%

6%

CONCACAF

325

179

64%

36%

CONMEBOL

308

192

62%

38%

OFC

65

28

70%

30%

UEFA

327

60

84%

16%

total matches

1.962

280

88%

12%

K=40: WC and continental qualifiers and major tournaments

against

confed

own confed

other confed

own confed

other confed

AFC

3.683

147

96%

4%

CAF

4.465

70

98%

2%

CONCACAF

2.327

11

100%

0%

CONMEBOL

691

15

98%

2%

OFC

454

63

88%

12%

UEFA

4.913

22

100%

0%

total matches

16.533

164

99%

1%

K=30: all other tournaments

against

confed

own confed

other confed

own confed

other confed

AFC

851

483

64%

36%

CAF

688

281

71%

29%

CONCACAF

202

178

53%

47%

CONMEBOL

62

171

27%

73%

OFC

103

88

54%

46%

UEFA

333

331

50%

50%

total matches

2.239

768

79%

25%

K=20: friendly matches

against

confed

own confed

other confed

own confed

other confed

AFC

1.323

1.399

49%

51%

CAF

1.960

907

68%

32%

CONCACAF

1.008

1.200

46%

54%

CONMEBOL

357

1.273

22%

78%

OFC

92

216

30%

70%

UEFA

2.766

1.897

59%

41%

total matches

7.506

3.346

69%

31%


Observations:

  • in general 85% of all matches is intraconfederational;
  • CONMEBOL with their 10 member NT's plays the most against teams from other confederations (56%);
  • CAF with their 54 member NT's plays the least against teams from other confederations (16%);
  • in World Cup matches (60) the interconfederational percentage is logically (because partly forced in the group stage) the highest: 74%;
  • continental finals (50) and qualifiers matches (40) are by nature the match types with the lowest percentage interconfederational matches (resp. 12% and 1%);
  • the 'friendly' match types (30 and 20) show higher percentages interconfederational matches again with resp. 25% and 31%.


I determined for each year from 1980 until 2022 the compete elo-ranking on January 1st, so position and rating points per team. No longer existing teams were, where applicable, renamed to their current name: West-Germany became Germany, Burma became Myanmar etc. Otherwise no longer existing countries (f.i. East-Germany) and also non-FIFA members are left out of this analysis.

With the dissolution of the Soviet-Union, Czechoslovakia and Yugoslavia a lot of new European countries were created in the beginning of the nineties. I followed the customary line of reasoning in this and considered respectively Russia, Czech Republic and Serbia the rightful successors of these former states.


In order to be able to analyze trends in average elo ratings for the top-x teams per confederation I determined per confederation a ranking of teams based on the average elo ranking position of each team over all 43 year rankings:


rank in UEFA

team

avg pos

rank in CAF

team

avg pos

1

Germany

5,0

1

Nigeria

42,1

2

Netherlands

6,4

2

Egypt

44,3

3

France

6,5

3

Cameroon

46,6

4

Spain

6,7

4

Ivory Coast

47,6

5

England

6,9

5

South Africa

48,1

6

Italy

7,0

6

Morocco

49,4

7

Croatia

12,8

7

Ghana

52,8

8

Portugal

14,0

8

Tunisia

55,2

9

Russia

16,5

9

Algeria

58,5

10

Denmark

16,6

10

Senegal

60,2

11

Czech Republic

17,5

11

Zambia

69,0

12

Sweden

17,9

12

Dem. Rep. of Congo

76,3

13

Serbia

17,9

13

Mali

80,5

14

Belgium

21,8

14

Libya

80,7

15

Romania

22,6

15

Guinea

85,0

16

Republic of Ireland

25,5

16

Uganda

88,7

17

Poland

25,9

17

Zimbabwe

89,9

18

Switzerland

27,4

18

Angola

90,7

19

Scotland

31,9

19

Gabon

92,7

20

Ukraine

32,9

20

Congo

95,6

21

Norway

36,1

21

Burkina Faso

97,4

22

Greece

36,4

22

Togo

100,6

23

Austria

37,5

23

Kenya

102,1

24

Bulgaria

37,9

24

Malawi

106,9

25

Turkey

39,3

25

Madagascar

110,1

26

Wales

40,1

26

Sudan

110,9

27

Slovakia

41,5

27

Sierra Leone

110,9

28

Hungary

42,7

28

Ethiopia

115,9

29

Israel

47,3

29

Liberia

116,4

30

Bosnia and Herzegovina

51,1

30

Gambia

121,1

31

Northern Ireland

54,8

31

Cape Verde

121,3

32

Slovenia

55,2

32

Mozambique

121,6

33

Montenegro

57,1

33

Tanzania

122,2

34

Finland

58,9

34

Benin

126,3

35

North Macedonia

63,3

35

Niger

128,6

36

Georgia

64,7

36

Burundi

129,3

37

Iceland

70,0

37

Guinea-Bissau

136,4

38

Belarus

78,5

38

Central African Republic

136,5

39

Albania

84,7

39

Chad

137,2

40

Azerbaijan

95,6

40

Namibia

137,9

41

Latvia

97,6

41

Rwanda

145,2

42

Kazakhstan

102,7

42

Mauritius

153,0

43

Cyprus

103,8

43

Botswana

154,4

44

Moldova

106,3

44

Lesotho

154,4

45

Kosovo

107,2

45

Eswatini

156,3

46

Armenia

111,0

46

Equatorial Guinea

158,0

47

Lithuania

113,6

47

Mauritania

158,3

48

Estonia

120,0

48

Eritrea

162,8

49

Malta

131,0

49

Somalia

174,6

50

Faroe Islands

147,9

50

São Tomé e Príncipe

176,5

51

Luxembourg

153,5

51

South Sudan

181,2

52

Liechtenstein

165,8

52

Seychelles

185,3

53

Gibraltar

178,3

53

Comoros

192,8

54

Andorra

183,3

54

Djibouti

197,8

55

San Marino

193,9

 

rank in AFC

team

avg pos

rank in CONCACAF

team

avg pos

1

Australia

33,0

1

Mexico

17,5

2

South Korea

35,5

2

United States

37,6

3

Iran

36,6

3

Costa Rica

48,5

4

Japan

47,7

4

Honduras

52,5

5

Iraq

54,0

5

Canada

60,2

6

Saudi Arabia

60,5

6

Guatemala

76,2

7

China

61,0

7

Trinidad and Tobago

82,6

8

Uzbekistan

61,0

8

Jamaica

82,8

9

Kuwait

74,3

9

El Salvador

83,4

10

North Korea

77,1

10

Cuba

87,9

11

Qatar

83,0

11

Haiti

96,6

12

Syria

90,1

12

Panama

99,7

13

United Arab Emirates

91,9

13

Suriname

124,0

14

Bahrain

101,0

14

Saint Vincent and the Grenadines

131,0

15

Jordan

105,1

15

Bermuda

133,6

16

Thailand

108,4

16

Grenada

137,1

17

Turkmenistan

115,5

17

Barbados

139,3

18

Oman

119,6

18

Curaçao

143,2

19

Lebanon

123,3

19

Guyana

151,1

20

Tajikistan

123,8

20

Saint Kitts and Nevis

152,0

21

Vietnam

133,8

21

Saint Lucia

152,0

22

Palestine

139,8

22

Antigua and Barbuda

155,7

23

Indonesia

140,7

23

Dominica

165,9

24

Malaysia

141,8

24

Belize

169,5

25

Hong Kong

142,9

25

Dominican Republic

172,6

26

Singapore

143,0

26

Aruba

175,8

27

Yemen

150,4

27

Nicaragua

176,7

28

Kyrgyzstan

156,7

28

Cayman Islands

181,8

29

Myanmar

159,2

29

Puerto Rico

185,1

30

India

160,5

30

Bahamas

196,5

31

Cambodia

171,8

31

British Virgin Islands

200,0

32

Chinese Taipei

179,8

32

Turks and Caicos

209,3

33

Pakistan

185,0

33

Montserrat

214,3

34

Bangladesh

185,5

34

US Virgin Islands

216,3

35

Philippines

190,8

35

Anguilla

222,3

36

Maldives

191,8

37

Afghanistan

192,9

38

Macau

194,9

39

Laos

195,0

40

Nepal

195,5

41

Sri Lanka

197,0

42

Mongolia

200,4

43

Brunei

205,7

44

Guam

209,2

45

Bhutan

218,1

46

Timor-Leste

224,7


rank in CONMEBOL

team

avg pos

rank in OFC

team

avg pos

1

Brazil

2,7

1

New Zealand

72,3

2

Argentina

7,1

2

Tahiti

110,8

3

Uruguay

17,9

3

Fiji

121,3

4

Colombia

24,4

4

New Caledonia

134,0

5

Chile

26,3

5

Solomon Islands

147,9

6

Paraguay

27,6

6

Vanuatu

165,7

7

Peru

41,5

7

Papua New Guinea

170,9

8

Ecuador

41,9

8

Cook Islands

210,7

9

Bolivia

57,7

9

Samoa

211,8

10

Venezuela

77,0

10

Tonga

212,1

11

American Samoa

223,8


In a graph:




Below are the graphs with the average elo rating over the top-x teams in each confederation.


For the top-10 teams:




For the top-20 teams:




For the top-30 teams:




Observations:

  • UEFA is in all top-x categories the confederation with the highest average rating over all the analyzed years;
  • the top-10 teams average rating for AFC, CAF and CONMEBOL lies close together over all the years;
  • when we take more teams in consideration CAF and AFC drop a little in average rating (logically) compared to CONMEBOL. You can see that AFC climbs towards the CAF average rating for the top 20 teams during the eighties and nineties;
  • for the top-30 teams you can see that CAF has an consistent higher average rating than AFC;
  • for the top-10 teams CONCACAF is already lower in average rating than AFC, CAF and CONMEBOL and drops even further away when more than 10 teams are considered.


Another research aspect is the trend over the years in rating difference between for instance UEFA and the other confederations. I've taken UEFA as reference because you can see above that their average rating over the years is nearly constant.

I've put a linear trend line in each graph to easily see if the rating difference is growing of shrinking over the years. For these graphs I consider the average ratings for the top-30 teams so it's only relevant for CAF, AFC and CONCACAF:










Observations:

  • the rating difference for top-30 teams between UEFA and AFC is definitely diminishing over the years;
  • for CAF it is slightly growing;
  • for CONCACAF it is rapidly growing.

Conclusions:
  • if a shrinking difference in average rating between two confederations is a sign of underestimation of the strength of the teams in the weaker confederation then not teams from CAF but from AFC are evidently underrated by elo;
  • but we also see that for CAF and CONCACAF the average rating difference is growing. Should we then conclude that teams from these confederations are overrated by elo ? No, I think that elo has no regional bias nor is busy adjusting for that regional bias. It is just a sign of confederations becoming stronger of weaker over the years.
  • What's in my opinion a strong indicator for the somewhat low elo ratings for CAF's top teams might be the consistently high average rating of the top-30 teams in Africa. The average level of NT's in CAF is stronger than in AFC or in CONCACAF, so points loss by Africa's top teams is simply more likely to occur.


About me:

Software engineer, happily unmarried and non-religious. You won't find me on Twitter or other so called social media. Dutchman, joined the blog in March 2018.

1 comment:

  1. In the last year or so, I've seen 3 potential data points that I find most convincing around Elo having a regionalization problem.
    1- Brazil/Argentina's colossal World Cup winning odds
    2- Senegal's relatively low rating despite being African champions
    3- Large difference in rating between elo and betting markets on Asian teams (particularly Iran)

    When delving into the data though (which you've done a very good job at presenting here) all of these things can be explained through just looking at results.
    Brazil and Argentina went undefeated (except to one another) in a very hard CONMEBOL region. Teams in Europe who would be challengers at the WC crown generally did not do that in UEFA.
    Senegal has losses and ties to particularly low rated teams (mid-to-high level sides in CAF, but a challenger for the WC should not be dropping points to Guinea, I believe)
    And we will certainly see on Iran, et al. I wouldn't be surprised if they challenge in group B, but they are certainly better sides than betting markets have them (dead last in the field).
    Thanks as always for your analysis

    ReplyDelete