Comparison of the Quality of Assessments Using Continuous and Discrete Ordinal Rating Scales

There are various types of rating scales in which the possible responses are either continuous or discrete. A large number of studies have compared the visual analogue scale (VAS) with various types of discrete scales, such as verbal descriptor scales and numerical rating scales. These studies have reported conflicting results, with no firm evidence of superiority of either type of scale. However, the conclusions have often been based on parametric statistical methods. In the present study, a rank-invariant approach for inter-scale comparisons is used to evaluate the order consistency between the VAS, the graphic rating scale and a five-point verbal descriptor scale. The comparative evaluation showed that both the verbal descriptor scale and the graphic rating scale assessments were superior to the visual analogue scale assessments, and that assessments on the discrete scale had the highest level of stability.