The category effect with rating scales: Number of categories, number of stimuli, and method of presentation.

Abstract

Squares receive higher category ratings when the smaller sizes are presented more frequently than the larger sizes.This shift in the rating scale is greater when there are either fewer categories (the Category Effect) or more stimuli.Similar shifts were obtained whether the stimuli were presented successively for judgment or simultaneously.The Category Effect also occurred when subjects were not told how many categories to use until after the contextual stimuli had been presented.A simple range-frequency model describes most of the shifts in scale by variations in a single weighting parameter.However, these shifts are predicted by an elaborated model in which the number of representations of any stimulus in working memory is limited by a principle of consistent assignment of each stimulus to a single category.This elaborated model correctly predicts the disapearance of the Category Effect when contexts are manipulated by varying the spacing of stimulus values rather than by varying their relative frequencies.Category ratings are probably the most frequently used of dependent variables in psychological research, perhaps because they reflect the way people ordinarily express value judgments.In opinion surveys, in personality inventories, and also in a wide variety of laboratory experiments, subjects make ratings using a prescribed set of categories.How many categories?It is commonly believed that the specific number of categories is unimportant, for example, that the scale of judgment for three categories is simply a linear transformation of the scale for nine categories.This assumption of the equivalence of scales is sometimes wrong.Compare the two panels of Figure 1, which plot the effects of a contextual manipulation on ratings of the same five squares, using either three or nine categories.Both panels show typical contextual effects: Ratings of the same stimuli are higher when the distribution of contextual frequencies is positively skewed (i.e., when the smaller squares occur with greater frequency).However, the effects of this contextual skewing are more than twice as great when subjects are restricted to just small, medium, and large than when they are permitted to use nine different categories from very, very small to very, very large.This difference in the magnitude of the contextual effect suggests that the number of categories may be a crucial consideration in research using category ratings as a dependent variable.For example, in food research where tasters rate the sweetness of different soft drinks, the same drink might be reported as below medium sweetness using one set of categories but above medium sweetness using a set with a different number of categories.How is sensitivity to the skewing of the distribution of contextual stimuli affected by the number of categories and the num-We are grateful to Michael H.