In psychophysics, a method of scaling in which pairs of stimuli are presented, every stimulus in the set being paired with every other stimulus, a judgement being made in each case as to which of the two is greater with regard to the attribute being scaled (for example, which is heavier, brighter, or preferable). Provided the judgements satisfy certain assumptions, an ordinal scale is established. The technique is practical only if the number of stimuli is relatively small, because the number of pairs in a set of n stimuli is n!/2(n − 2)! and hence for n = 8 there are 28 pairs, for n = 10 there are 45 pairs, for n = 20 there are 190 pairs, for n = 50 there are 1,225 pairs, and so on. See also unfolding technique.