Objective: The aim of this study was to determine the theoretical repeatability coefficient of a 100 mm visual analog scale (VAS) in children in different circumstances.
Methods: A prospective cohort study was conducted using a convenience sample of patients aged 8 to 17 years presenting to a pediatric emergency department. Patients were asked how they liked a variety of foods (surrogate for stable pain stimulus) on a 100 mm VAS with 4 different sets of questions repeated 3 times: set 1—questions at 3-minute intervals with no specific instructions other than how to complete the VAS; set 2—same format as set 1 except for the duration of the interval (1 min); set 3—same as set 1 except patients were asked to remember their answers; set 4—same as set 1 except patients were shown their previous answers. For each, the repeatability coefficient of the VAS was determined.
Results: A total of 100 patients aged 12.1±2.4 years were enrolled. The repeatability coefficient for the questions asked at the 3-minute interval was 12 mm, whereas it was 8 mm when asked at the 1-minute interval. When asked to remember their previous answers or to reproduce them, the repeatability coefficients for the questions were 7 and 6 mm, respectively.
Discussion: The conditions of the assessments influence the repeatability coefficient of the VAS. Depending on different circumstances, the repeatability coefficient in children aged 8 to 17 years varies from 6 to 12 mm on a 100 mm VAS.