User segmentation
In the Proba.ai service the possibility of participants segmentation of the experiment is realized. Users are divided into new and old ones based on the app installation date received from the device.
The app installation date is compared with the experiment start date, then the service distributes the users according to the variants. By default, new users are those whose installation date is later than the experiment start date.

The app installation date transfer is implemented through the deviceProperties structure, where the installedAt key is added, for example (Swift):
"deviceProperties": {
    "installedAt": "2021-05-20T09:55:05.000+03:00"
 }
The property name and time format must be specified correctly when the key is set.
If the device transmits to installedAt the installation date, which is earlier than the experiment start date, that user is considered to be old. Then the user does not get any variant from the server, a default version is used. Thus, old users do not fall into the target segment of the experiment (for the experiment on new users only).

The app installation date is not always possible to obtain by normal methods. In this case, after the sdk initialization, and the subsequent start of the experiment, all users are considered new, as instead of the actual installation date the service will use the date of the device’s first interaction with the server (the start date of the first experiment). Therefore such users will be considered new in the first experiment, and in all subsequent ones - old.