Abstract
Purpose: :
Analogue scales are frequently employed as a means of allowing subjects 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 judge the reproducibility of paper– and computer–based (tablet PC) analogue scales in order to better understand the variability in data provided by an individual using an analogue scale.
Methods: :
30 subjects rated ocular comfort, redness, and clarity of vision on a 10cm non–demarcated horizontal line on paper and a tablet PC. The line was converted to a 1 to 100 scale. Measurements were taken in the morning between the hours of 8:30 and 10:30am and again the same day between 2:30 and 4:30pm.
Results: :
The mean difference between the measures for the two media was 1.80 units, with the tablet PC having the higher mean measure. The coefficient of repeatability (2SD of the differences) was 8.22 units, and the 95% confidence interval (2SE of the difference) was 0.54 units. This suggests a slight positive bias of 1.80 ± 0.54 for the tablet PC. The Precision of 8.22 (2SD) is within what we considered to be a clinically significant change, 10 units.
Conclusions: :
Discrepancy analysis yielded no significant difference and slight bias between paper– and computer–based analogue scales. These results suggest that the choice of medium does not significantly influence the outcome for subjective analogue scales.
Keywords: clinical research methodology • contact lens • conjunctiva