In CrossEngage, you can test sending the outbound message against skipping it. Users that receive the campaign are called the Target Group, those who do not are the Control Group.
You can turn on this option in Campaign setup tab in campaign configuration (Campaigns → Edit → Campaign Setup). The percentage you define is the share of recipients in your segment that will not receive any message when campaign runs.
Please consider the following when evaluating the campaign results:
Once a user is assigned to a group, either Target Group or Control Group, this does not change over the time anymore - user is attached to the group throughout the lifecycle of the campaign.
Control Group works more precisely with larger number of recipients. Should your segment include less than 100 users, the results may be not perfectly accurate.
Frequency cappings, both on campaign level and global level, may have an impact on delivering messages to both Target Group and Control Group.
When measuring target vs control group performance using your campaign goal, it's important to remember that if the goal is related to the message you are sending (for example a click on an email), the control group won't be able to complete it and campaign metrics might look misleading.
Should you want to access the list of users that were assigned to the control group in a specific campaign, please follow these steps:
Create a new segment
Add an event-based condition. The event you need is called Message Dispatch Failed Because Of Control Group. Its occurrence should be greater than 0.
Add the event property CampaignId, then insert the ID of the finished campaign where you activated the control group.
Save the segment.