The Psychometric Properties of the Visual Analogue Scale Applied by an Observer to Assess Procedural Pain in Infants and Young Children: An Observational Study

Published:February 06, 2021DOI:


      • VASobs scores were sensitive and responsive to procedural pain.
      • Clinicians were not confident about the clinical utility of the scores.
      • VASobs scores for procedural pain assessment show poor reliability.
      • VASobs scores did not distinguish adequately between pain and distress.
      • This scale cannot be recommended for research or clinical use.



      The Visual Analogue Scale applied by an observer (VASobs) is widely used to quantify pain but the evidence to support validity is poor. The aim of this study was to evaluate the psychometric and practical properties of the VASobs used to assess procedural pain in infants and young children.

      Design and methods

      In an observational study, 26 clinicians applied the VASobs independently to video segments of 100 children aged six to 42 months undergoing a procedure to generate pain and distress scores. Each video segment was scored by four randomly selected reviewers.


      Reliability for pain scores was poor to fair (ICC 0.35 to 0.55) but higher for distress scores (ICC 0.6 to 0.89). At a cut-off score of 3, sensitivity and specificity were 84.7% and 95.0%, respectively for pain and 91.5% and 77.5% respectively for distress. Linear mixed modelling confirmed responsiveness. An increase in pain scores (regression slope 4.95) and distress scores (regression slope 5.52) across phases (baseline to procedure) was seen for painful procedures. The correlation between VASobs pain and FLACC scores was good (r = 0.74) and correlations between VASobs distress and FLACC scores were excellent (r = 0.89).


      VASobs was easily applied and preferred by clinicians. Despite evidence of sensitivity and responsiveness to pain, the reliability results were poor, and this scale cannot be recommended for use.

      Practice implications

      The results of this study prevent recommending the VASobs for assessing procedural pain in infants and young children for clinical or research purposes.


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