Every platform reports in its own currency and credits itself for the same sale. The totals overstate by design, never reconcile to the P&L, and cannot carry an investment decision. The uncomfortable part is that the platforms reporting the performance are the platforms selling the media. The incentive to overstate is built in.

Incrementality testing and marketing mix modeling are trusted, rigorous ways to measure causality, and they belong in any serious program. Each captures only part of the picture, and a formal incrementality test takes real time and budget to run. Triangulating across methods is how you get to a read you can act on.

A causal multiplier rescales a platform's self-reported result toward what a channel actually drove. Deriving that multiplier from post-purchase survey responses, the customer telling you what moved them, adds a third triangulation input with two practical advantages: it is fast and it is low cost. You get a causal estimate for every channel in days, with no media held back, and it reaches the places click-based tracking struggles most: small channels, and offline media like TV/CTV and podcasts.

No single method is complete, so the strongest read triangulates all three. Survey multipliers give a current read, surface long-tail and offline channels, and help you see where a full incrementality test earns its time and budget. Used together, they get you to a confident number faster.