Sensitivity and accuracy of the visual analogue scale: a psycho-physical classroom experiment

Abstract

1 Twenty-seven intelligent volunteers took part in a classroom experiment on two occasions to assess subjectively, ordinally related volumes of sound (offered in random sequence), using the visual analogue scale. 2 It was simple to use and largely acceptable. Big differences were significant by parametric tests but small ones were sometimes significant only with ordinal ones. Within-subject comparisons were more accurate and more sensitive than those between-subjects. The t-test was very robust. 3 Five out of 49 results were erroneously significant; they remained so no matter how the data were handled. It was concluded that this was due to a shift in either perception, cognition or scoring between the two sessions. 4 Arcsine transformations made little difference. The mechanism of these is fully discussed. A conversion to proportional scores resulted in very much improved sensitivity. 5 It is recommended that authors using the visual analogue scale: have valid reason in their own setting for using a transformation; present the distribution, or at least the medians and ranges of their raw scores; also use a simple but different measure so as to demonstrate internal consistency between them.