Can I set a holdout group for a lookalike prospecting campaign?
Yes! If you have enabled holdouts for your prospecting campaign, you can take a holdout of 20% at no additional charge. We highly recommend taking a holdout, because having incremental lift metrics will help you understand the true return on the campaign.
If the option to take a holdout doesn't appear in the lookalike modeling flow, double check the feature is enabled for the campaign. To do this, go back to the campaign Overview page and click "Edit Campaign" (right-hand column).