How does Firebase Analytics define a “user” (for purposes of Audience)?

Question

I\'ve been told that, \"Once a user is in an audience, they will forever be in that audience\". I\'m curious how long is \"forever,\" in the context of a user? For instance,

Answer 1

Too late but for somebody.
Follow google support's User-ID and Cross Device. And About the User-ID feature details about benefits of having our own User ID.

Steve Ganems's answer is right. Without user id, user's uniqueness is based on app's instance. Once it is lost(uninstalled), that user is lost. So obviously the app in different device is considered as a distinct user.

From doc:

Without user ID, a search on a phone one day, purchase on a laptop three days later, and request for customer service on a tablet a month after that are counted as three unique users in a standard Analytics implementation, even if all those actions took place while a user was signed in to an account.

When you implement User-ID, you can identify related actions and devices and connect these seemingly independent data points. That same search on a phone, purchase on a laptop, and re-engagement on a tablet that previously looked like three unrelated actions on unrelated devices can now be understood as one user’s interactions with your business.

Answer 2

In Firebase Analytics, a User is synonymous with an instance of an app. So:

1. If your app is installed on Device A, then uninstalled, then re-installed on Device A, you will have two distinct Users.

2. If your app is installed on Device A and then later on Device B, that counts as two distinct Users.