What Causes a ROAS Shift in Paid Media?
A ROAS shift usually comes from one of four sources: last-click attribution undercounting the channels that built the sale, a cross-channel or marketplace sale that goes uncounted, a channel scaling past the point where extra spend still returns proportionally, or a budget decision in one channel shifting another channel's reported ROAS. These causes can look identical in a topline ROAS number. Isolating which one occurred, then checking it against factors like seasonality or promotions, is what separates a genuine performance change from a measurement artifact.
Measurement Fundamentals

