In a press conference prior to the 2015 World Championship final, Whalen "Riot Magus" Rozelle, head of esports at Riot Games, made the claim that "there's been a more diverse champion pool than we've ever seen at Worlds before." In looking solely at champions picked, he's correct. The 2015 World Championship games saw 74 unique champions picked. The closest number of unique champions picked in other World Championships is 68 during Season 3.

Yet champions picked isn't the only way to measure champion pool diversity. This is the first year, for example, that two champions have comprised more than 50% of red side bans, with Gangplank and Mordekaiser considered the uncontested strongest picks on the patch. It's also the only World Championship where two first pick options have comprised more than 50% of champions first picked in Elise and Rek'Sai with certain jungle options standing out as the most dominant.

The purpose of this investigation is to look across measures of champion pool diversity for the past five world championships. The general conclusion is that the 2015 World Championship only had the most diverse champion pool in "majority picks," and only passes the 2014 World Championship in most metrics, but falls behind Seasons 1-3.

Assessing champion diversity based on raw tallies

Unique champions by category in each World Championship

WC Champions picked Bans Red side bans First picks Red side first rotations Last picks W1 46 26 22 16 21 22 W2 55 34 31 12 25 21 W3 68 37 32 16 26 36 W4 59 33 29 14 27 37 W5 74 38 23 13 29 35

The 2015 World Championships has the highest number of unique picks, bans, and red side first rotations, but is near the lowest in red side bans, first picks, and is third in last picks. Even in categories where the 2015 World Championship leads, ban and last pick diversity don't seem significantly large relative to pick diversity.

A lot of first pick, ban, and red side rotation numbers across World Championships are close as there's frequently a handful of champions that are much stronger than others on the patch. In the first World Championship, Rumble comprised 14% of red side bans, Nunu was most frequently first picked, and Janna was selected most often in red side first rotations.

In the second World Championship, Ezreal was first picked in 29% of games, Anivia and Jayce were most frequently banned on red side, and Sona most frequently picked in red side first rotations. The Season 3 World Championship saw Shen first picked in 25% of games, Corki and Elise comprising 27% of red side first rotation picks, and Zed taking up 21% of red side bans.

The 2014 World Championship saw Alistar banned on red side in 46 of 78 games, Lee Sin first picked in 23% of games, and Kha'Zix comprising 19% of red side first rotation picks. This most recent World Championship had the highest extreme of first picks and red side ban concentration, as already mentioned. Darius, Gragas, and Rek'Sai were the champions most picked in red side first rotation.

Adjusting for changes in champion availability and games played

There are several reasons why looking at just the raw numbers can be misleading. It's an interesting thought to look at unique champions picked or banned, but the landscape of League of Legends has changed over time.

Champions available have increased from 76 at the first World Championship to 126 for most of the 2015 World Championship (since Gragas, Ziggs, and Lux could have been played prior to semifinals, they're included in the total champions available). The number of games has also increased since the first World Championship, with 28 games played in the Season 1 World Championship, 31 games played in Season 2, 63 games played in Season 3, 78 games played in 2014, and 73 in 2015.

As already illustrated, concentrations of picks also dictate the diversity. If 74 champions are picked, but most are picked only as one-offs, and most games feature the same seven or eight champions, it's hard to call the champion pool truly diverse.

Unique selections as a percentage of champions pickable on the patch

WC Champions picked Bans Red side bans First picks First rotations Last picks W1 60.53% 34.21% 28.95% 21.05% 27.63% 28.95% W2 52.88% 32.69% 29.81% 11.54% 24.04% 20.19% W3 59.65% 32.46% 28.07% 14.04% 22.81% 31.58% W4 49.17% 27.50% 24.17% 11.67% 22.50% 30.83% W5 58.73% 30.16% 18.25% 10.32% 23.02% 27.78%

When one looks at unique selections in each category as a percentage of champions available on the patch which the World Championship is played, we see a different story. The 2015 World Championship is the third most diverse in terms of champions picked of champions available on the patch after Season 1 and Season 3 Worlds. It's the fourth most diverse in unique champions banned, the least diverse in red side bans and first picks, the third most diverse in unique first rotations, and the fourth in unique last picks.

In terms of representing the patch on which the tournament was played, the most recent World Championship doesn't capture the widest variety of champions. One may argue that this is because it's harder to capture more champions in a similar event, but as the amount of games has grown as well, this argument has less ground. The ratio of games played to champions available has actually grown since the Season 1 World Championship from .37 to .58. It was the highest in 2014 at .65. This should theoretically make it possible for more of the total champions available to be played.

Unique champions per game played

WC Champions picked Bans Red side bans First picks First rotations Last picks W1 1.64 0.93 0.79 0.57 0.75 0.79 W2 1.77 1.10 1.00 0.39 0.81 0.68 W3 1.08 0.59 0.51 0.25 0.41 0.57 W4 0.76 0.42 0.37 0.18 0.35 0.47 W5 1.01 0.52 0.32 0.18 0.40 0.48

In terms of unique champions in each category per game played, there's a decline after the Season 3 World Championship. The only World Championship in which there were fewer unique picks per game in each category is the 2014 World Championship. Otherwise, 2015 seems relatively close in amounts to Season 3 and much less diverse than Season 1 or Season 2.

Concentration of picks

The final metric to look at to gauge diversity of the World Championships is concentration of picks. By ordering champions in each Worlds by most picked in a category, we get a sense for how frequently the major picks come into play. The following table shows the amount of "most selected" in each category comprise more than 50% of champions in that category.

WC Champions picked Bans Red side bans First picks First rotations Last picks W1 10 6 6 5 7 9 W2 12 8 8 3 6 7 W3 11 7 5 4 6 10 W4 11 5 4 3 5 10 W5 13 5 2 2 6 10

The numbers of champions that comprise more than 50% of champions picked, bans, red side bans, first picks, first rotations, and last picks have stayed relatively close with minimal differences. As already illustrated, the most alarming change is that only 2 champions comprise more than 50% of red side bans and first picks.

Otherwise, the amount of champions frequently banned, first rotated, and last picked have stayed relatively similar across World Championships. The one category where 2015 looks more diverse is that 13 champions most frequently picked comprised more than 50% of picks at Worlds. The 13 most frequently picked champions at the 2015 World Championship were as follows:

Champion Times picked %Total picks Elise 39 5.34 Darius 38 5.21 Rek'sai 37 5.07 Alistar 30 4.11 Gragas 29 3.98 Jinx 29 3.98 Kalista 29 3.98 Thresh 29 3.98 Tristana 27 3.70 Lulu 26 3.56 Braum 21 2.88 Fiora 19 2.6 Gnar 19 2.6

*Note that Sivir was also played 19 times, but these 13 comprise more than 50% of champions played without her.

There is increased diversity in the amount of champions picked most frequently, but very clear first pick favoritism made some early draft phases more predictable. Two more champions don't make the increase in pool of champions picked most frequently significantly higher in order to compensate for stagnation in early ban and pick strategies, but it is more worth celebrating than raw numbers.

Adjusting for experimental picks

The 2015 World Championship was also played on a patch where competitive matches had not been played prior to the event. This could falsely inflate the true pick diversity, as many teams may have played champions they weren't confident would work well in the meta one or two times to get a feel for what was really strong.

To check for this behavior, we first count all champions picked once or twice at the World Championships to see if the number is higher in 2015. We then also look at number of unique champions played per game during the Bracket Stage when most teams have a strong feel for what they want to play at that point.

Number of champions picked only once or twice by World Championship

WC Champions picked 1 or 2 times W1 16 W2 17 W3 22 W4 17 W5 20

The World Championship in Season 3 also saw teams playing on a relatively changed patch from qualifiers with recent Trinity Force buffs, so seeing similar amounts of champions picked once or twice in both years somewhat supports the theory that there was more experimentation. That said, there weren't significantly more champions picked only one or two times this year than last year. It's still worth noting the small increase that could inflate a perception of champion pool diversity if teams are playing champions that turned out to actually not be strong on the patch.

Unique picks in bracket stage at each World Championship

WC Unique bracket stage picks Bracket games played Picks-Games W1 39 16 2.44 W2 49 19 2.58 W3 43 22 1.95 W4 45 28 1.61 W5 45 24 1.86

Unique picks in bracket stage are relatively similar across World Championships despite certain differences in games played. A lot of unique or experimental picks from Group Stages were shaved down in the 2015 World Championship and didn't appear again.

The 2015 World Championship bracket stage had 1.86 unique picks per game, down from 2.44 in Season 1, 2.58 in Season 2, and 1.95 in Season 3. Even though the Season 2 bracket stage had fewer games played at 22, there were 49 unique champions picked in bracket stage relative to 45 in 24 games in 2015.

Conclusion

It's clear that the 2015 World Championship isn't definitively the Worlds with the most diverse champion pool. There have been more unique champions picked this recent Worlds, but that doesn't mean that the general pool has been more diverse.

It is refreshing to see that the 13 most picked champions comprised 50% of the pool when previously the highest number of most picked champions necessary to comprise the majority was 11. That does show an increase in diversity, but it's the only metric in which the 2015 World Championship clearly stands out.

Most troubling, the number of champions first picked or banned on red side was very small. This suggested a selection of champions that were clearly stronger than the others, limiting diversity in early stages of champion select.

There were also a large amount of champions picked only once or twice relative to all other years except 2013, pointing to one off experimentation in Group Stage. Outside Group Stage, unique champions picked aligned well with 2013 and 2014, suggesting that teams had an idea of the true champion pool that performed well on the patch at that stage.

It is worth noting that, outside of early phases of draft, the 2015 World Championship appeared much more diverse in the context of champions available and number of games played than the 2014 World Championship. 2015 World Championship diversity is otherwise either about the same or lower than Season 1-3 World Championships.

As to why diversity in the 2015 World Championship didn't improve much and actually seems to be in decline by some measures from Seasons 1-3, there are several explanations. One is that more champions makes the patch more difficult to balance. Another is that precision in drafting has improved over time. In the case of the latter, the 2015 World Championship should be celebrated for improved diversity over 2014 in all phases but early drafting. In the former, the idea that diversity has greatly improved this year is incredibly overstated.

In some ways, it feels as if the patch was altered significantly from 5.15, the patch on which most leagues played their qualifier, to try to falsely inflate champion pool diversity at Worlds. Teams unsure of how to play the patch might have experimented more, giving viewers an interesting experience. Because of the failure to balance extremely strong picks like Mordekaiser and Gangplank, however, the gamble backfired.

While I'm not sure if this was Riot's goal, it's something to consider for patching in the context of next year's tournament.

Kelsey Moser is a staff writer for theScore eSports. You can follow her on Twitter.