Session instrument
Extreme-user interview
Measures: What the average user struggles to verbalise
It serves when you already know something is wrong and nobody can name what. Whoever is at the edge of use describes precisely what the person in the middle has already swallowed in silence. And it is the method that comes closest to the question of The body: almost every law on this site was measured in the middle of the curve, and the edge is precisely where it stops holding.
The method comes from design thinking, and the d.school handbook is explicit about a point that tends to get lost: the goal is not to build for those people. It is to use what they can verbalise to find the problem the user in the middle cannot put into words, and then check which of it resonates with the people you actually serve. The need at the edge usually overlaps with the need in the middle, but that is a result, not a rule.
How to run itRecruit the two ends of the spectrum for that task, not for the audience: those with the least repertoire in it and those with the most. Interview them as you would interview anyone, but look for workarounds: an invented shortcut, a note on paper, a parallel spreadsheet. Every workaround is a requirement the product did not meet. Five to seven people per end are usually enough.
SeesIt brings out needs that research with the average audience does not produce, because whoever is in the middle has already got used to the defect and no longer mentions it.
Does not seeWhat the edge asks for does not always serve the middle. Without the step of checking what resonates with the main audience, the method becomes an excuse to build what one interviewee asked for.