A new approach to category scales of intensity II:: Use of d′ values

Using a Rank-Rating method, d' values were obtained for stimuli from a model system using 15-point, 9-point, 7-point and 5-point category scales. For an apple/grape juice system, d' values were compared for 9-point and 7-point scales. There was general agreement on d' values among the scales, except where stimuli had their scores 'bunched' into one category: this tended to occur for the strongest and weakest stimuli for Rank-Rating and for the scales with fewer points. Bunching altered distribution variances and distorted the calculated d' values. Further study gave d' values for the discrimination of confusable stimuli, using paired-comparison and rating data, thus providing numerical measures of their relative sensitivity.