Control and personalization groups

[Control group](https://ru.wikipedia.org/wiki/Control_group НЕТ ТАКИХ СТАТЕЙ) are those users for whom we chose the random personalization option.

The personalized group is those users for whom the optimal personalization option was selected (based on the machine learning model)

This separation is used for several purposes.

Firstly, the separation into control and personalization groups allows us to evaluate the quality of personalization. Specifically, answer the question "how much does personalization increase conversion?".

Secondly, the control group data is used to train the machine learning models.