How are related apps calculated in android market

Someone can give some information about how related apps 开发者_如何学Care calculated in android market? Why for example X is related to Y but Y isn't related to X?

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I've not seen Google publish any details of this, and I wouldn't expect them to as it's commercially sensitive, but I expect the algorithm takes into account some or all of these:

• Apps with similar names
• Apps that comes up together in searches
• Apps that are often viewed in the same session by users
• Apps that have both been bought/installed by the same person
• Apps that are in the same category

The algorithm will share some characteristics with the algorithm Amazon uses to recommend similar products.

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I've seen descriptions of apps where the developer simply stated "similar to the following apps: ... " and listed them all.

Now that the length for descriptions has been increased, this would seem like a decent solution to accurately define similar apps.