Does the control group include my existing users, and how do I get a different group?

Yes. Turning a control group on applies to your entire user base right away, not only to people who sign up afterward. There is no gradual catch-up.

Pushwoosh doesn't store a list of members. On every check it combines your app, the group's version number, the group, and the user ID, turns them into a number with a hash formula, and puts the user in the control group if the number falls within the percentage you set. As a result:

• A user stays in or out until you reshuffle the group or change its size, the user's ID changes, or an Auto-refresh cycle or Experiment ends.
• If you disable the group and turn it on again without reshuffling, you get exactly the same users.
• Contact methods without a User ID are never excluded, so register every contact method for a person under one User ID.

To pick a new random set of users at the same percentage:

1. Open the control group and click the three-dot menu in the top right.
2. Select Reshuffle control group and confirm.

Reshuffling also restarts the measurement window for control group analytics: data from before the reshuffle isn't included in later comparisons.

Learn more: How control group membership works