Comparison of conditional quality of life terminology and visual analogue scale measurements

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Abstract
Two common formats for grading quality of life parameters are descriptive choices (mild, moderate, severe) and visual analogue scales. However the quantitative relationship between descriptive terminology and visual analogue scale scores has not been determined. A content neutral questionnaire was administered to 213 evaluable subjects who were asked to place the descriptors ‘mildly’, ‘moderately’, and ‘severely’ (presented in random order) on 100mm visual analogue scales. Visual analogue scales were presented without and then with hashmarks at 25mm, 50mm, and 75mm. Median visual analogue scale values for the descriptive terms differed significantly without hashmarks (‘mildly’=24mm’, ‘moderately’=43mm, ‘severely’=84mm; pp<0.001). Comparison of interquartile range values (25th–75th percentile) revealed a distinct meaning for ‘severely’ (68–93mm) but marked overlap between ‘mildly’ (10–45mm) and ‘moderately’ (22–53mm). Errors of order (order other than ‘mildly’ < ‘moderately’ < ‘severely’) were made by 91 subjects. The discrepancy ‘moderately’ < ‘mildly’ accounted for most of these errors (72 subjects). Median values for ‘mildly’, ‘moderately’, and ‘severely’ are distinct and approximately linear on a visual analogue scale for large populations. However there is significant confusion between the terms ‘mildly’ and ‘moderately’ for individual subjects. Visual analogue scales can reveal finer quantitative differences than descriptive terms but require a significant time commitment for instruction and administration. Descriptive terms on a word-graphic scale or descriptive terms with numerical values to reenforce order of severity (0=absent, 1=‘mildly’, 2=‘moderately’, 3=‘severely’) may be reasonable alternatives.