Does Thirty-Minute Standardised Training Improve the Inter-Observer Reliability of the Horse Grimace Scale (HGS)? A Case Study.
Authors: Dai Francesca, Leach Mattew, MacRae Amelia Mari, Minero Michela, Costa Emanuela Dalla
Journal: Animals : an open access journal from MDPI
Summary
# Editorial Summary: Horse Grimace Scale Training Effectiveness The Horse Grimace Scale offers a standardised, objective method for identifying acute pain through facial expression analysis, yet its clinical utility depends entirely on assessor competency—a gap this case study sought to address by testing whether half an hour of structured training could meaningfully improve reliability amongst observers lacking equine experience. Two hundred and six undergraduate students with no horse handling background scored ten facial photographs before and after receiving a 30-minute, expert-led training session covering the six Facial Action Units (FAUs) that comprise the HGS. Whilst pre-training agreement was poor across most FAUs (Cohen's κ ranging from 0.20 to 0.68), two areas showed substantial post-training improvement: stiffly backwards ears and orbital tightening both reached Cohen's κ values of 0.90–0.91 (p < 0.001), indicating near-perfect concordance with the expert assessor. Despite these encouraging gains in specific facial markers, the authors conclude that 30 minutes is insufficient preparation for untrained observers to reliably apply the full HGS across all six FAUs, though the training protocol establishes a solid foundation upon which more comprehensive programmes could be built. For practitioners integrating HGS into clinical pain assessment, these findings underline the importance of investing in formal, sustained training rather than relying on brief instruction—particularly when identifying subtle pain indicators remains crucial to welfare and treatment decisions.
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Practical Takeaways
- •The Horse Grimace Scale can be improved with training, but 30 minutes is not enough for inexperienced observers to use it reliably for clinical pain assessment
- •Some facial action units (backwards ears, orbital tightening) are learnable with brief training, while others require more extensive instruction
- •Training programs for HGS should be substantially longer and more comprehensive than 30 minutes if the goal is consistent pain identification across multiple assessors
Key Findings
- •Pre-training Cohen's k values ranged from 0.20 to 0.68 across six Facial Action Units of the Horse Grimace Scale
- •Post-training, stiffly backwards ears and orbital tightening showed significant improvement with Cohen's k values of 0.90 and 0.91 respectively (p < 0.001)
- •Thirty-minute standardised training was insufficient for observers without horse experience to reliably apply the Horse Grimace Scale independently
- •Standardised training provides a foundation but requires additional comprehensive training to achieve adequate inter-observer reliability