The 9-point hedonic scale: Are words and numbers compatible?

Abstract

The original 9-point scale, developed by the U.S. army for menu planning for their canteens, consisted of a series of nine verbal categories representing degrees of liking from ‘dislike extremely’ to ‘like extremely’. For subsequent quantitative and statistical analysis, the verbal categories are generally converted to numerical values: ‘like extremely’ as ‘9’, ‘dislike extremely’ as ‘1’. Yet, sometimes what is termed a 9-point hedonic scale is an unstructured numerical scale, labeled at the ends with ‘dislike extremely’ and ‘like extremely’. The former scale requires consumers to categorize foods according to how much they are liked or not; the latter requires the consumers to differentiate numerically between the foods in terms of the relative degree of liking for each. Foods that were placed in the same verbal category for the former scale might be given different numerical scores on the second scale. To illustrate this, consumers rated five chocolates, in a series of experiments, on these two types of 9-point scale (verbal categories only vs numbers only) and the proportion responding differently to the two scales ranged from 100% to 79%. This indicated that numerical data obtained from both types of 9-point scale were not interchangeable. It also suggested that consumers were using different cognitive strategies for verbal categories and numbers. To check that the difference was not caused by the fact that the verbal categories were bipolar and the numbers unipolar, the experiment was repeated using a bipolar number scale (–4 through 0 to +4). The same results were obtained. For comparison, a 9-point hedonic scale including both verbal categories and numbers together, was also used. The results for this scale showed a greater similarity to the version of the 9-point scale consisting only of verbal categories than the unstructured numerical version. Stimulus equalizing bias was used as a tool to make a preliminary investigation into the cognitive strategies involved for the two versions of the scale. The hypothesized relative strategy was confirmed for the unstructured numerical scale but the hypothesized absolute strategy was not confirmed for the scale using only verbal categories; the strategy appeared to have relative elements. Regardless of the precise nature of the cognitive strategies used for two versions of the scale, they do not give the same results and data obtained from each version should be compared with caution.