To assess validity and reliability for a visual analogue scale (VAS) used by owners to measure chronic pain in their osteoarthritic dogs.
68, 61, and 34 owners who completed a questionnaire.
Owners answered questionnaires at 5 time points. Criterion validity of the VAS was evaluated for all dogs in the intended-to-treat population by correlating scores for the VAS with scores for the validated Helsinki Chronic Pain Index (HCPI) and a relative quality-of-life scale. Intraclass correlation was used to assess repeatability of the pain VAS at 2 baseline evaluations. To determine sensitivity to change and face validity of the VAS, 2 blinded, randomized control groups (17 dogs receiving carprofen and 17 receiving a placebo) were analyzed over time.
Significant correlations existed between the VAS score and the quality-of-life scale and HCPI scores. Intraclass coefficient (r = 0.72; 95% confidence interval, 0.57 to 0.82) for the VAS indicated good repeatability. In the carprofen and placebo groups, there was poor correlation between the 2 pain evaluation methods (VAS and HCPI items) at the baseline evaluation, but the correlation improved in the carprofen group over time. No correlation was detected for the placebo group over time.
Although valid and reliable, the pain VAS was a poor tool for untrained owners because of poor face validity (ie, owners could not recognize their dogs' behavior as signs of pain). Only after owners had seen pain diminish and then return (after starting and discontinuing NSAID use) did the VAS have face validity.