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Visual analog scales facilitate small changes in dry eye responses
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A continuous visual analog scale has a high degree of sensitivity and discriminating capacity that detects smaller symptom changes in dry eye syndrome, according to a review by Charles W. McMonnies, DSc, in Optometry and Vision Science.
Furthermore, a 100-point visual analog scale is appropriate for repeated measures and within-patient comparisons, he wrote.
By switching between visual analog scales and Likert scales, researchers risk interpretation problems among patients, McMonnies said.
“It is recommended that visual analog scales not be used as a single measurement of a multidimensional construct but rather be used in conjunction with other instruments that reflect the construct’s multidimensionality,” he wrote.
He also described the importance of an activity interference assessment, which includes reading, watching television, using a computer, daytime driving, night driving, performing housework or professional work, for example.
He suggested that visual analog scales are better suited to within-subject repeated measurement and for measuring change.
McMonnies also found that the time reference when measuring responses to treatment is usually lacking in surveys of dry eye symptoms. A patient should be asked to provide an assessment of any symptom changes over the entire period since the last assessment, he explained. In Likert scales, marginal changes in statements can have significant effects on survey results.
Sense of well-being and mood can also affect subjective responses, he said. – by Abigail Sutton
Disclosure: McMonnies reported no financial disclosures.
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