title: The impact of test medium on use of visual analogue scales.
abstract: OBJECTIVE
  Visual analog scales are frequently used as a means of allowing participants to rate symptoms during clinical trials. The accuracy and reproducibility of these scales play an important role in determining the experimental value of the data they provide. This study was initiated to compare the data collected using paper- and computer-based (Tablet PC) analog scales to better understand the variability in data provided by a visual analog scale.
  
  
  METHODS
  Thirty participants rated ocular comfort, redness, and clarity of vision (right and left eyes) on a nondemarcated horizontal line on both paper and a Tablet PC. Measurements were taken in the morning between the hours of 8:30 and 10:30 am and again the same day between 2:30 and 4:30 pm.
  
  
  RESULTS
  The mean difference between the measures recorded in the morning for the 2 media was 2.6 +/- 0.9 (confidence intervals, 2 standard errors of the differences) units on a 100 unit scale, with the Tablet PC having the higher mean measure. The limits of agreement (2 standard deviations of the differences) was 9.4 units. Comparing the difference of the differences (1.0 +/- 1.3) between the 2 methods of measure (morning vs. afternoon) the visual analog scales on the Tablet PC seemed to have good reproducibility of agreement in comparison with the paper version.
  
  
  CONCLUSIONS
  Discrepancy analysis yielded no significant difference and slight bias between paper- and computer-based analog scales. Repeatability of measures using the Tablet PC was also demonstrated. These results suggest that the choice of medium does not significantly influence the outcome for subjective analog scales.
authors.affiliation: Centre for Contact Lens Research, School of Optometry, University of Waterloo, Waterloo, Canada. cawoods@sciborg.uwaterloo.ca
authors.forename: Craig A
authors.initials: CA
authors.lastname: Woods
authors.forename: Brad
authors.initials: B
authors.lastname: Cumming
mesh_terms: D000328:Adult; D006801:Humans; D008838:Microcomputers; D008875:Middle Aged; D010147:Pain Measurement / Q000379:methods* / Q000592:standards; D010209:Paper; D015203:Reproducibility of Results; D055815:Young Adult