What does pre-post testing measure in P Max campaigns?

Pre-post testing in Performance Max (P Max) campaigns primarily measures the uplift in conversions. This method involves assessing the performance of a campaign before its implementation (the "pre" phase) and comparing it to performance data after running the campaign (the "post" phase).

The key focus of this testing is to analyze how the campaign has impacted conversion rates, indicating the effectiveness of the advertising efforts. By measuring the differences in conversion metrics before and after the campaign, marketers can assess the direct impact of their strategies and optimizations. This analysis helps in understanding the return on investment (ROI) and overall performance improvements resulting from the advertising efforts.

While other metrics such as campaign budget efficiency, customer engagement rates, and ad quality scores are important for evaluating different aspects of a campaign, they do not specifically capture the direct change in conversion outcomes that pre-post testing aims to analyze. Hence, the uplift in conversions is the most relevant measure in this context.