Judgments are made by pairwise comparison; perceived magnitude is recovered from relative rather than absolute assessments.
Thurstone's 1927 method underlies modern rating scales and paired-comparison testing. Its practical value is that people compare far more reliably than they rate on absolute scales.
In practice
- A wine panel asked to rank eleven bottles disagrees; asked to compare pairs, the same panel produces a stable ordering.
- A recruitment shortlist scored absolutely is inconsistent between panellists, and the same panellists agree on head-to-head comparisons.