After the first game of the group stage of the World Cup, there were a lot of discussions about the chances of qualification of every team. At this moment, Costa Rica was still an outsider and England was still in the race for qualification. Then, some experts gave the two following stats:
85% of teams that won their first group stage game move to next round” and “9% of teams that lost their first group stage game move to next round”.
When you read this, it seems the first game completely determines the chances of qualification. But does it really?
Many reasons could explain this first game advantage. A team that wins the first game could have a psychological advantage over the next opponents or could simply have a confidence boost for the next games. To see if the first game really gives such a momentum, I investigated the two other games.
Methodology
I took the group stage of the last five World Cups (1998-2002-2006-2010-2014) and searched the set of teams that won the first/second/third game for each World Cup. Within this set, I looked for the subset of teams that qualified. Then, I counted the number of teams of all qualifying subsets and of all first-match-winning sets to obtain a qualification ratio. The data comes from the data set described in the first football article (from Soccerway.com and Football-Data.co.uk).
Statistics
I followed the same procedure for draws and losses, and I produced the following table:
| Game | Win | Draw | Loss |
|---|---|---|---|
| First game | 0.85 | 0.55 | 0.12 |
| Second game | 0.80 | 0.54 | 0.16 |
| Third game | 0.77 | 0.53 | 0.22 |
As a complement, I also computed the average number of points needed to go to next round:
| Group spot | Average number of points needed to go to knockout stage |
|---|---|
| Winner | 7.40 |
| Runner-up | 4.98 |
Caveat: The sample size is 5 World Cups only ! I cannot take World Cups before 1998 because the format of the competition changed that year. Also, please note that the ratios given by experts (85% and 9%) were perfectly accurate at the time they were published. Indeed, they couldn’t use Brazil 2014 before its group stage was finished.
Analysis
Using the statistics extracted in the previous part, I could fact-check the initial claim of the TV pundits:
- When you take a look at the first table, the first game is not as impressive as it seemed. Even if you compare it to the third game when some teams have already qualified, the difference is insignificant.
- The second table establishes a symbolic safety mark at 5 points.
- A specific result in any game has a massive influence on reaching the 5 points safety mark given the small number of fixtures. For example, losing a game forces the team to win the two remaining games to be above the safety mark.
Conclusion: With such a small number of games, all points are important and none should be neglected. The first game doesn’t contribute more to qualification than the others.