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Updated: Jun 20, 2026
A Protocol of Manual Tests to Measure Sensation and Pain in Humans
Published on: December 19, 2016
Reliability and validity of observer ratings of pain using the visual analog scale (VAS) in infants undergoing
Anna Taddio1, Lisa O'Brien, Moshe Ipp
1Leslie Dan Faculty of Pharmacy, University of Toronto, and Child Health Evaluative Sciences, The Hospital for Sick Children, Toronto, Ont., Canada. anna.taddio@utoronto.ca
Insights
The visual analog scale (VAS) shows promise for measuring infant pain during immunizations. However, rater experience and focus can influence results, affecting conclusions on pain relief effectiveness.
Area of Science:
- Pediatrics
- Pain Management
- Clinical Research Methodology
Background:
- Assessing acute procedural pain in infants is challenging.
- Observer-rated pain scales are crucial for evaluating interventions.
- The visual analog scale (VAS) is a commonly used pain assessment tool.
Purpose of the Study:
- To evaluate the reliability and validity of the visual analog scale (VAS) for observer-rated pain in infants during immunization.
- To compare real-time versus videotape assessments of infant pain using the VAS.
- To investigate factors influencing VAS reliability and its utility in assessing analgesic effectiveness.
Main Methods:
- A double-blind randomized controlled trial involving 120 infants.
- Pain was assessed using a 100mm unmarked VAS by four raters (physicians and non-physicians).
- Intra- and inter-rater reliability were calculated using the intra-class correlation coefficient (ICC); criterion validity was assessed against the Modified Behavioural Pain Scale.
Main Results:
- High intra- and inter-rater reliability (ICC: 0.69-0.91 and 0.55-0.97) were observed for the VAS.
- No significant bias was found between real-time and videotape assessments.
- Criterion validity was strong (rho: 0.81-0.94) when compared to the Modified Behavioural Pain Scale.
- Amethocaine reduced injection pain scores, particularly for non-physician raters.
Conclusions:
- The VAS demonstrates initial support as an outcome measure for acute procedural pain in infants.
- Variability in rater experience and focus can impact conclusions regarding analgesic effectiveness.
- Further research is needed to standardize VAS use and interpretation in pediatric pain assessment.
Abstract:
We tested the reliability and validity of observer-rated pain in infants undergoing immunization using the visual analog scale (VAS). Pain was assessed in real time and later, from videotapes, in 120 1-year-old infants participating in a double-blind randomized controlled trial of amethocaine vs. placebo. Altogether, 2 (1 physician, 1 non-physician) of 4 raters [2 physicians, 2 non-physicians (nurse and graduate student)] independently assessed baseline and vaccine injection pain using a 100mm unmarked VAS line. Intra- and inter-rater reliability, assessed using the intra-class correlation coefficient (ICC), ranged from 0.69 to 0.91 and 0.55 to 0.97, respectively. Bland-Altman plots demonstrated no evidence of bias between real time and video assessments. When scores were dichotomized into 2 groups (no pain and pain) using a cut-off of >or=30mm, intra-rater reliability ranged from 0.35 to 0.92. The percent of scores deviating by >20mm was 4.5-14.29%. Criterion validity was demonstrated by correlations between the VAS and Modified Behavioural Pain Scale, a validated observational measure; (rho: 0.81-0.94). Injection scores were lower in the amethocaine group, when comparing difference (baseline-injection) or dichotomized scores; significance (p<0.036) was achieved for non-physician scores, but not physician scores. Together, these results provide initial support for the VAS as an outcome measure for acute procedural pain in infants. However, different conclusions may be reached about the effectiveness of analgesic interventions depending on the rater. Sources of variability include use of multiple raters, rater focus (procedure vs. child) and experience level.
