Equivalence of Paper and Touch Screen Versions of the EQ-5D Visual Analog Scale (EQ-VAS)

Abstract

The EQ-VAS, a measure of self-reported health status, has been operationalized in ways that depart from the original format. The primary purpose of the study was to examine the equivalence of the original paper-based vertical format with a touch screenbased horizontal format. Non-probability sampling was used to recruit 314 subjects intended to reflect the primary socio-demographic characteristics of the general adult population. A two-part questionnaire completed roughly 10 minutes apart was administered in a randomized crossover design. One part was the original paper-based 20cm vertical EQ-VAS; the other part was touch screen computer-based (designed by Assist Technologies) and included, among other items/scales, a horizontal EQ-VAS, the SF-36, and socio-demographic items. A mean difference of ± eight points between the two versions was specified as the minimally important difference (MID). Almost a third (30.1%) of the respondents reported identical scores on both formats and 80.1% of the respondents had difference scores within ± 8 points. The 95% confidence intervals for both samples indicated that the difference in scores was relatively small and below our equivalence threshold. In addition, data collected via touch screen may be more reliable since 22% of subjects did not complete the EQ-VAS paper format as instructed. These results provided evidence for the measurement equivalence of the touch screen EQ-VAS with the original paper format. A secondary purpose was to examine the psychometric properties of an electronic version of the SF-36. Floor and ceiling effects were comparable to that observed in other studies using the paper SF-36 in the general population. All reliability coefficients exceeded 0.70; the range was from 0.75 to 0.93. There was support for the construct validity of the touch screen SF-36, as the direction and strength of the correlations between the SF-36 scales and the EQ-5D domains were as hypothesized. Overall, there was a high level of correspondence between the touch screen SF-36 scores and previously reported paper based SF-36 scores in the general population. The comparable psychometric properties and low level of missing data make touch screen questionnaires a very viable alternative to their paper-based formats.