Psychometric evaluation of a visual analog scale for the assessment of anxiety
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RESEARCH
Psychometric evaluation of a visual analog scale for the assessment of anxiety Research
Valerie SL Williams*1, Robert J Morlock2 and Douglas Feltner3
Abstract Background: Fast-acting medications for the management of anxiety are important to patients and society. Measuring early onset, however, requires a sensitive and clinically responsive tool. This study evaluates the psychometric properties of a patient-reported Global Anxiety - Visual Analog Scale (GA-VAS). Methods: Data from a double-blind, randomized, placebo-controlled study of lorazepam and paroxetine in patients with Generalized Anxiety Disorder were analyzed to assess the reliability, validity, responsiveness, and utility of the GAVAS. The GA-VAS was completed at clinic visits and at home during the first week of treatment. Targeted psychometric analyses—test-retest reliabilities, validity correlations, responsiveness statistics, and minimum important differences—were conducted. Results: The GA-VAS correlates well with other anxiety measures, at Week 4, r = 0.60 (p < 0.0001) with the Hamilton Rating Scale for Anxiety and r = 0.74 (p < 0.0001) with the Hospital Anxiety and Depression Scale - Anxiety subscale. In terms of convergent and divergent validity, the GA-VAS correlated -0.54 (p < 0.0001), -0.48 (p < 0.0001), and -0.68 (p < 0.0001) with the SF-36 Emotional Role, Social Function, and Mental Health subscales, respectively, but correlated much lower with the SF-36 physical functioning subscales. Preliminary minimum important difference estimates cluster between 10 and 15 mm. Conclusions: The GA-VAS is capable of validly and effectively capturing a reduction in anxiety as quickly as 24 hours post-dose. Single-item visual analog scales (VASs) have been used in psychological assessment since the early 20th century and have subsequently been employed successfully in the assessment of a wide variety of health-related constructs including pain [1-3], quality-of-life [4,5], and mood [6-8]. VASs are brief and simple to administer and minimal in terms of respondent burden. These characteristics make them ideal for use in a diary format questionnaire where patients frequently record symptoms and outcomes. VASs are particularly useful when assessing a single construct with many perceptible gradations and research has shown that unipolar VASs ("Not at all Anxious" to "Extremely Anxious") are more easily understood than bipolar VASs ("Extremely Calm" to "Extremely Anxious") [9]. Although a VAS may be oriented vertically, the most common form is a horizontal line. In fact, horizontal * Correspondence: [email protected] 1
RTI Health Solutions, 3040 Cornwallis Road, Research Triangle Park NC 27707 USA
Full list of author information is available at the end of the article
scales have been shown to produce a more uniform distribution of scores and to be more sensitive than vertical scales [3,10]. Multiple-item VASs are often shown to have high internal consistency [10]; however, there is wide variability in test-retest reliabilities—VAS test
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