Repertory grid technique lets each subject generate their own descriptive dimensions via triadic comparisons.

Evidence

Repertory grid technique (Kelly, 1955): The basic idea of this technique is to get subjects to define their own constructs by asking them to describe the ways in which elements and their associated meanings vary. This is done, for example, by presenting three samples, where each assessor states the characteristic for which two of the samples are similar to each other and different from the third. — Ville Pulkki, Matti Karjalainen, Communication Acoustics- An…, 941

Categorization

• XREF: Triadic elicitation (two similar, one different) resembles the method of sorted triads used in personal construct psychology and in some creativity research.