Testing the measurement equivalence of paper and touch-screen versions of the EQ-5D visual analog scale (EQ VAS)

Objectives This study examined the measurement equivalence of the original paper-based vertical format of the EQ-5D visual analog scale (EQ VAS) with a touch-screen computer-based horizontal format. Methods A total of 314 subjects were administered two modes of the EQ VAS in a randomized crossover design. One mode was the original paper-based 20 cm vertical EQ VAS; the other mode was touch-screen-based. Measurement equivalence was assessed by testing the 95% confidence interval of the mean differences from an equivalence threshold of -3 to +3 points on the VAS and evaluating the intraclass correlation coefficient (ICC). Results The adjusted mean (SE) EQ VAS score was 80.96 (0.87) on the paper and 79.59 (0.85) on the touch-screen. The mean (CI) difference between scores on the two formats was 1.37 with a confidence interval of 0.175-2.559, wholly contained within the equivalence interval. The ICC was 0.75, indicating acceptable agreement between the two modes. Almost a third (30.1%) of the respondents reported identical scores on both formats. Conclusion These results provide evidence for the measurement equivalence of this EQ VAS touch-screen administration mode with the original paper mode.