The folks behind Steam suddenly have yet another weird consideration to make around the store’s recommendation algorithm: positive review bombs. In April, Ubisoft gave away Assassin’s Creed Unity for a week in the wake of the Notre-Dame fire, and the game consequently received a rash of positive reviews, many of which had little to do with Unity itself.

Valve has decided against dropping Unity’s positive review score, in part because it wouldn’t affect the game’s visibility much – but the blog post also gives us a rare bit of insight into how the store’s algorithm works. “Games receive a ‘boost’ based upon which user review bucket they’re in (Mixed, Mostly Positive, etc). The actual boost amount is quite small relative to other factors in the Store, and it’s essentially the same for all the Mixed or above review buckets.”

But, Valve says, “there’s a big boost drop-off as soon as a game drops below Mixed into the negative buckets, which occurs at the point where less than 40% of the user reviews are positive. A Mixed game receives over 500% more boost than a game in Mostly Negative.” 71.7% of games on Steam are rated at least ‘mixed.’

Earlier this year, Valve implemented a policy against “off-topic” Steam review bombs, and as a result targeted review campaigns over, say, a developer’s personal comments wouldn’t affect the game’s final user score. Borderlands games got review bombed over the Borderlands 3 going to the Epic Store, and those ratings no longer count toward the game’s final score.

Valve has continually focused on the “off-topic” nature of these reviews, and by that definition the wave of positive Unity reviews referencing the giveaway or Ubisoft’s donation to reconstruction of the monument constitutes an off-topic review bomb. But Valve writes in the announcement that most reviews “look like standard reviews of a new player, or a player that’s returning to a product they bought a while ago.”

Unity has received a lot of updates after its disappointing launch, and Valve says “it appears that some players who bounced off it at launch have returned, and found themselves enjoying the game more.”

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On top of that, Valve says context changes can change the value of a game, too. “In this case, the Notre Dame tragedy has made it so that AC:Unity happens to now include the world’s best virtual recreation of the undamaged monument. That’s a context change that could be increasing the value players are getting from the game, so perhaps the game really is better than it was before?”

While Unity will continue to enjoy the modest benefit of its positive reviews, Valve still hasn’t decided what to do if similarly positive review bombs happen in the future.