Grimace scales need to undergo several steps of validation to ensure they measure what they are supposed to measure (in this case pain, and not other negative emotions such as fear or anxiety). These tools must be reliable (i.e. different individuals give similar scores, or the same individual gives similar scores across time) and responsive to treatment (e.g. pain scores should decrease after treatment of pain). These characteristics (e.g. validity, reliability) are called \u2018measurement properties\u2019. In Dr Paulo Steagall\u2019s study published in journal \u201cPain\u201d, the research team used robust scientific criteria to evaluate the quality of the measurement properties of grimace scales available for nonhuman mammals \u2013 a process referred to as \u2018systematic review\u2019 of the literature.<\/p>\n\n\n\n
A large search of the literature identified scientific studies reporting the development and validation of grimace scales in non-human mammals. Thereafter, two researchers independently evaluated whether measurement properties were reported in these studies and whether the methods used were appropriate. A consensus was reached and scores were given to each measurement property for each study, and then to each grimace scale. Therefore, each grimace scale received an overall classification of high, moderate, or low strength of evidence, indicating whether that tool can be used with confidence with appropriate validity, reliability according to the highest scientific standards.<\/p>\n\n\n\n
The study found 52 studies involving 12 different grimace scales for 9 species (mice, rats, rabbits, horses, piglets, sheep or lamb, ferrets, cats, and donkeys) with considerable variability regarding their measurement properties. From these, the Mouse, Rat, Horse and Feline Grimace Scales exhibited high level of evidence. The Rabbit, Lamb, Piglet and Ferret Grimace Scales and Sheep Pain Facial Expression Scale exhibited moderate level of evidence. Other scales for sheep, horses and donkeys exhibited low level of evidence.<\/p>\n\n\n\n
Gaps in the literature were identified to guide future studies to improve the measurement properties of current grimace scales and standards of pain management in animals with an ultimate impact in their welfare.<\/p>\n\n\n\n