APA Dictionary of Psychology

a study in which the researcher asks participants to make a series of comparisons among stimuli (such as pictures, words, or emotions) so that the stimuli can be ordered on some dimension of interest (e.g., size, preference, cost, importance). For example, a researcher conducting a marketing study might ask respondents to indicate their preferences among certain products by ranking them from most likely to buy to least likely to buy, or by comparing two products at a time and indicating which would be preferred.