What's a control group?

The correct option is It's a group separated from the rest of the experiment because a control group serves as the essential baseline for measuring the true causal impact, or incrementality, of a marketing intervention. In the context of offline sales, this group consists of users or geographic regions that are intentionally withheld from seeing a specific ad campaign, allowing advertisers to compare their "natural" behavior against the "test group" that was exposed to the ads. By maintaining this strict separation, businesses can isolate the actual lift in store visits or sales directly attributable to their digital spend, filtering out external factors like seasonality or organic brand awareness that would have driven conversions regardless of the advertisement. Would you like me to explain how to determine the optimal size for a control group to ensure your experiment results are statistically significant?