At which point during the campaign management timeline should an advertiser establish KPIs?

Establishing Key Performance Indicators (KPIs) is a critical step during the "Setup" phase of campaign management. KPIs define what success looks like for the campaign and provide measurable targets. Setting them at the beginning ensures that the campaign is designed with clear objectives, allowing for proper tracking and evaluation throughout its lifecycle. Without clearly defined KPIs during setup, it's impossible to accurately assess performance during the "Review," "Optimize," or "Report" phases, as there would be no benchmarks against which to measure. "Review" and "Report" phases use established KPIs to evaluate performance, while "Optimize" adjusts the campaign to better achieve those KPIs.