PloS one2021; 16(8); e0255618; doi: 10.1371/journal.pone.0255618

A critical evaluation for validation of composite and unidimensional postoperative pain scales in horses.

Abstract: Proper pain therapy requires adequate pain assessment. This study evaluated the reliability and validity of the Unesp-Botucatu horse acute pain scale (UHAPS), the Orthopedic Composite Pain Scale (CPS) and unidimensional scales in horses admitted for orthopedic and soft tissue surgery. Forty-two horses were assessed and videotaped before surgery, up to 4 hours postoperatively, up to 3 hours after analgesic treatment, and 24 hours postoperatively (168 video clips). After six evaluators viewing each edited video clip twice in random order at a 20-day interval, they chose whether analgesia would be indicated and applied the Simple Descriptive, Numeric and Visual Analog scales, CPS, and UHAPS. For all evaluators, intra-observer reliability of UHAPS and CPS ranged from 0.70 to 0.97. Reproducibility was variable among the evaluators and ranged from poor to very good for all scales. Principal component analysis showed a weak association among 50% and 62% of the UHAPS and CPS items, respectively. Criterion validity based on Spearman correlation among all scales was above 0.67. Internal consistency was minimally acceptable (0.51-0.64). Item-total correlation was acceptable (0.3-0.7) for 50% and 38% of UHAPS and CPS items, respectively. UHAPS and CPS were specific (90% and 79% respectively), but both were not sensitive (43 and 38%, respectively). Construct validity (responsiveness) was confirmed for all scales because pain scores increased after surgery. The cut-off point for rescue analgesia was ≥ 5 and ≥ 7 for the UHAPS and CPS, respectively. All scales presented adequate repeatability, criterion validity, and partial responsiveness. Both composite scales showed poor association among items, minimally acceptable internal consistency, and weak sensitivity, indicating that they are suboptimal instruments for assessing postoperative pain. Both composite scales require further refinement with the exclusion of redundant or needless items and reduction of their maximum score applied to each item or should be replaced by other tools.
Publication Date: 2021-08-05 PubMed ID: 34352001PubMed Central: PMC8341545DOI: 10.1371/journal.pone.0255618Google Scholar: Lookup
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  • Journal Article
  • Research Support
  • Non-U.S. Gov't
  • Validation Study


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The research article aims to assess the reliability and validity of pain scales, namely Unesp-Botucatu horse acute pain scale (UHAPS), Orthopedic Composite Pain Scale (CPS), and unidimensional scales, used in horses following orthopedic and soft tissue surgeries. The findings suggest that the composite scales used are suboptimal and require further development to improve their sensitivity and adequacy in pain assessment.


  • 42 horses admitted for orthopedic and soft tissue surgery were assessed and their behaviors were videotaped at four different intervals: before surgery, up to 4 hours post-surgery, up to 3 hours after administering analgesic treatment, and 24 hours post-surgery, resulting in 168 video clips.
  • These clips are then viewed twice in random order, after a gap of 20 days, by six evaluators. Each evaluator would decide if the horses needed analgesia and used the Simple Descriptive, Numeric and Visual Analog scales, CPS, and UHAPS to assess the pain.


  • The intra-observer reliability of UHAPS and CPS ranged from 0.70 to 0.97, indicating that evaluators were consistent with their scores. Reproducibility, or the ability to mimic results by different evaluators, varied from poor to excellent across all scales.
  • Principal Component Analysis showed a weak association among 50% of UHAPS and 62% of the CPS items. This indicates a low level of correlation or relationship between different factors tallied in the pain scales.
  • All scales demonstrated satisfactory criterion validity, where correlation was above 0.67. However, internal consistency, which measures the correlation between different items in a test, was barely adequate (0.51-0.64).
  • Item-total correlation, which assesses the correlation of each test item with the total score, was satisfactory for 50% and 38% of the UHAPS and CPS items, respectively.
  • UHAPS and CPS showed high specificity (ability to correctly identify those without pain; 90% and 79%, respectively), but showed low sensitivity (ability to correctly determine those with pain; 43% and 38%, respectively).
  • All scales provided evidence of construct validity, as pain scores increased after surgery. The cut-off point for rescue analgesia was ≥ 5 for UHAPS and ≥ 7 for CPS.


  • Though the pain scales demonstrated repeatability, adequate criterion validity, and partial responsiveness, their internal consistency and sensitivity were suboptimal.
  • The association among elements in both UHAPS and CPS was poor, indicating further refinement is required. Unnecessary components could be removed, and the maximum score of each item could be decreased.
  • Alternatively, these tools could be replaced with alternative, more efficacious tools for assessing postoperative pain.

Cite This Article

Barreto da Rocha P, Driessen B, McDonnell SM, Hopster K, Zarucco L, Gozalo-Marcilla M, Hopster-Iversen C, Esteves Trindade PH, Gonzaga da Rocha TK, Taffarel MO, Alonso BB, Schauvliege S, Luna SPL. (2021). A critical evaluation for validation of composite and unidimensional postoperative pain scales in horses. PLoS One, 16(8), e0255618.


ISSN: 1932-6203
NlmUniqueID: 101285081
Country: United States
Language: English
Volume: 16
Issue: 8
Pages: e0255618
PII: e0255618

Researcher Affiliations

Barreto da Rocha, Paula
  • Department of Surgical Specialties and Anesthesiology, Medical School, Su00e3o Paulo State University (Unesp), Botucatu, Su00e3o Paulo, Brazil.
Driessen, Bernd
  • Department of Clinical Studies, New Bolton Center, School of Veterinary Medicine, University of Pennsylvania, Kennett Square, Pennsylvania, United States of America.
McDonnell, Sue M
  • Department of Clinical Studies, New Bolton Center, School of Veterinary Medicine, University of Pennsylvania, Kennett Square, Pennsylvania, United States of America.
Hopster, Klaus
  • Department of Clinical Studies, New Bolton Center, School of Veterinary Medicine, University of Pennsylvania, Kennett Square, Pennsylvania, United States of America.
Zarucco, Laura
  • Dipartimento di Scienze Veterinarie, Universitu00e0 degli Studi di Torino, Grugliasco, Italy.
Gozalo-Marcilla, Miguel
  • The Royal (Dick) School of Veterinary Studies and the Roslin Institute, The University of Edinburgh, Edinburgh, Midlothian, United Kingdom.
Hopster-Iversen, Charlotte
  • Department of Veterinary Clinical Sciences, Section of Medicine and Surgery, Faculty of Health and Medical Sciences, University of Copenhagen, Frederiksberg, Denmark.
Esteves Trindade, Pedro Henrique
  • Department of Veterinary Surgery and Animal Reproduction, School of Veterinary Medicine and Animal Science, Su00e3o Paulo State University (Unesp), Botucatu, Su00e3o Paulo, Brazil.
Gonzaga da Rocha, Thamiris Kristine
  • Department of Veterinary Surgery and Animal Reproduction, School of Veterinary Medicine and Animal Science, Su00e3o Paulo State University (Unesp), Botucatu, Su00e3o Paulo, Brazil.
Taffarel, Marilda Onghero
  • Department of Veterinary Medicine, Maringu00e1 State University, Maringu00e1, Paranu00e1, Brazil.
Alonso, Bruna Bodini
  • Faculty of Animal Science and Food Engineering, Sao Paulo State University, Botucatu, Brazil.
Schauvliege, Stijn
  • Department of Anesthesiology and Domestic Animal Surgery, Faculty of Veterinary Medicine, Ghent University, Ghent, Belgium.
Luna, Stelio Pacca Loureiro
  • Department of Veterinary Surgery and Animal Reproduction, School of Veterinary Medicine and Animal Science, Su00e3o Paulo State University (Unesp), Botucatu, Su00e3o Paulo, Brazil.

MeSH Terms

  • Animals
  • Female
  • Horse Diseases / diagnosis
  • Horse Diseases / surgery
  • Horses
  • Male
  • Pain Management / methods
  • Pain Management / veterinary
  • Pain Measurement / methods
  • Pain Measurement / veterinary
  • Pain, Postoperative / diagnosis
  • Pain, Postoperative / surgery
  • Pain, Postoperative / veterinary

Conflict of Interest Statement

Professor Bernd Driessen and Associate Professors Klaus Hopster and Laura Zarucco are shareholders of Narkovet Consulting®, LLC, which provided parts of the funding for the present study. However, Narkovet Consulting®, LLC did not in any way or form impact these authors’ adherence to all PLOS ONE policies on sharing data and materials as detailed in the online guide for authors ( or had any influence on data presentation and interpretation. All other authors declare that they have no conflicts of interest.


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