I intentionally moved away from using the NPS scale, which involves an eleven-point numerical scale ranging from 0 to 10. Drawing from my background in human factors, psychology, and user experience design, I learned that humans encounter difficulties in categorization when faced with more than six categories without a specific taxonomy to guide them. This isn’t a result of Miller’s “Magic Number 7” rather the work of Bousfield W.A. & A.K, and Cohen, B.H. between 1952 and 1966 on clustering.
For example, if you ask humans to rate something 1 to 10 they will struggle to create 10 distinct categories in their mind. When asked to devise their own taxonomy, or clusters, as lay people to the domain, they will tend to create no more than 6 categories. Hence, a scale of 0 through 5 is most appropriate for general consumption.
In my opinion, the NPS people tried this but discovered that in some cultures, such as Finland, people never give the top score on principle. They always choose the one below the best. Hence, the NPS reaction to this was to double the scale using 0 through 10 so that people could give a 9 when they are really giving a 4.5. My feeling on this is that it highlights the issues with numerical scales and undeclared taxonomies. The solution of doubling the scale, however, creates randomness in the system. It generates noise in the data reducing the signal strength, because of the general human issue of modeling categories against the scale. Fixing one problem, the cultural propensity never to give top ranking, creates another problem. There is a cognitive issue in the general population to struggle with more than 6 undeclared categories.
Hence, to avoid both problems, I am declaring the categories with narrative.