A product brief is still a hypothesis

A brief that says “customers want a faster version” has already chosen the answer. The study then becomes a hunt for quotes that agree.

Treat the brief as a claim that can fail. Write the opposite claim next to it. Design the sample and the questions so both can show up, including the dull middle where people do not care.

The useful readout is not a score. It is which part of the brief still stands, which part was a hope, and what you would not claim in the launch note.