1) Familiar to respondents
Giving (or receiving) a score out of 10 tends to be familiar to most customers/people – whether it be from tests at school, from the reviews of footballers in newspapers, or by thinking of it in terms of a percentage.
2) Allows more advanced analysis
Choosing a 10-point numerical scale allows us to perform more advanced analysis since it gives the scale interval data properties. This means that a one-point increase at any stage of the scale is equivalent, which cannot be assumed with verbal scales.
When using techniques such as correlation and regression this is an important advantage.
3) Ten points allow more choices and more discrimination
Respondents can feel constricted if there are too few response options – although this is primarily a problem when there are five or fewer choices.
More significant is the fact that satisfaction data tends to be negatively skewed (towards the upper end of the scale) – meaning that even with more than five choices the actual opportunity for discrimination is reduced. We recently exchanged views on this topic with Professor Johnson of the University of Michigan Business School and his response is shown below in full:
Professor Johnson is involved with the American Customer Satisfaction Index (ACSI), which also uses a ten point numerical scale.
“Our recommendations are based more on our experiences than any documented studies. But there are two articles that help directly or indirectly support the 10-point scales (see below). The first, by Ryan et al., compared 5 and 10 point scales to multi-item indices of 10-point scale. (Don’t be deceived by the title.) The second shows how satisfaction and quality data distributions have a generalisable negative skewness (i.e., most of the observations are toward the high end of the scale). This is why, to me, it makes sense to have more than just 7 scale points.
I hope this helps!
Ryan, Michael J., Thomas Buzas, and Venkatram Ramaswamy (1995), “Making Customer Satisfaction Measurement a Power Tool,” Marketing Research, 7 (Summer), 11-16.
Fornell, Claes (1995), “The Quality of Economic Output: Empirical Generalizations About Its Distribution and Association to Market Share,” Marketing Science, 14 (Summer), G203-G211.”
[Personal communication from Professor Michael Johnson of University of Michigan Business School, 12 September 2001].
4) It works
In our extensive experience it works! We specialise in customer satisfaction measurement and have conducted hundreds of customer satisfaction surveys using this scale, and we believe that it is the most suitable scale for measuring customer satisfaction. The 10-point scale has a finer distinction, which makes it easier to track changes and detect differences.