How Do You Know a Marketing Test Ran Long Enough?

[OwenF]

I find it hard to balance patience with wasted budget. Do you stop once a test reaches a minimum sample size, or also require it to run through a full weekly buying cycle?

 

[AmeliaFoster]

I set the stopping rule before launch: a minimum number of conversions, enough time to cover weekday and weekend behavior, and a spend ceiling. That prevents ending early after one strong day or letting a weak test run indefinitely.