By Rich Stone, 1 year ago
The TrueAchievements' forums and friend feeds have been buzzing this last couple of weeks with discussion about our new Ultimate Head to Head Contest.

It's safe to say the opening periods have been a great success, and we've had loads of fantastic feedback from the community - both happy to be playing some old forgotten gems, and delighted to be meeting new friends through the competition.

Many of you have asked us how we chose the match up pairings, and then the target achievement lists themselves. I thought it might be interesting to go through that process in a little more detail...

Scoring pairings
In order to choose the best possible matches, we needed to come up with a single numeric value that we could sort from. So for some Gamer A paired with some Gamer B, we needed to find a number that described how good a pairing they are for the contest.

In order to do that, we need to work out exactly what we think a perfect pairing needs to be....

We are trying to make a varied list of 20 achievements that are reasonably "fair" for both players. We can define fair in this case as if both players are at the same point in the game. Because we don't really have a way of determining that, we will use what we do have (and have lots and lots of ) - achievement data!

Therefore:

1. We can say an achievement choice in a game is fairest for both players when they have exactly the same set of achievements unlocked in a game.

We also want to have a few remaining achievements in the game to choose from to keep things interesting, so we will also add:

2. We think a game match is good when we have at least 3 of the same locked achievements available for both players

Plus we want to keep the target list as interesting and varied as possible, which means ideally having as many games in this state as possible.

3. We would like to choose from at least 20 "fair" games for generation of our target list

With these basic ideas in place, we could work on a formula - hooray!

Scoring a game
We decided to score each game for a pairing with a maximum score of 2 - made up of a factor for how close they were in their achievement unlocks and a (smaller) factor for having at least 3 achievements in the game still locked. The further their unlocked achievement lists were away from each other, the lower the score.

We could then compare all the games between Gamer A and Gamer B and choose the best 20 from those. Then add up those scores and we have a match up score out of 40 for the pair.

A perfect 40 is scored between a pair when they have at least 20 games from which they have unlocked exactly the same achievements, all of which have at least 3 achievements still to unlockWe then ran through and made a score for every gamer against every other gamer. With 1,735 valid entrants, that made over 3 million match up scores!. To give us time to generate all of those scores, we closed registration a few days before the contest actually started.

Matching the gamers
Once we had scores for every pairing, we went through and started pairing people up. We started with the people with the lowest best pairing, and matched those first. As pairs are created, they are obviously both removed from the possible matches for the next pairing. Choosing the gamers with the lowest best pairing first meant that we did the best we could to ensure everybody got a pairing that was at least "good". We could have chosen as many perfect pairings as possible instead, but that would have left loads of people that could not be matched at all.

From the 873 matches, we achieved a match score of at least 35 out of 40 for over 75% of the matches.
Another 20% had a score of between 33 and 35.
The final 5% of matches all had a score of above 25.
We'll give you more info on how we choose the target achievements next week, have a great weekend!
Written by Rich Stone
Creator of TrueAchievements, TrueTrophies and TrueSteamAchievements. Writes site news and still finds time for the odd game here and there. Loves Racing games and Shooters, yet to be convinced that any RPG is worth the time investment!