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

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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.

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