Comparison of three acute colic pain scales: Reliability, validity and usability

A valid, reliable and usable scale is needed for assessing severity of acute abdominal pain in horses. The study aim was to compare three different scales: (1) the equine acute abdominal pain scale (EAAPS); (2) a scale described by Mair and Smith (2005; M and S); and (3) a numerical rating scale (NRS). Forty brief films of horses (35 of colic cases and five of control horses) were randomly presented to 46 equine veterinarians from different countries. Participants, randomly divided into three groups, each used one scale. Five randomly selected films were shown twice for determining intra-observer reliability. Speed, ease of use and face validity of the scales were evaluated based on expert opinion. Response rate was excellent: 89% for the EAAPS (16/18), and 100% for the M and S (18/18) and NRS groups (10/10). The intraclass correlation (ICC) of 0.86 [95% confidence interval (CI); 0.80–0.92] for EAAPS indicated significantly better inter-observer reliability compared to 0.68 for the M and S and 0.71 for the NRS. Moreover, intra-observer reliability of EAAPS (weighted κ 0.95 [95%CI; 0.92–0.98]) was superior to the other scales (weighted κ 0.78, 0.77, for the M and S and NRS, respectively). Other validity measures (convergent, extreme group, predictive validities), usability (time taken to score the films − speed) and the ease of use of the scales were not significantly different. Face validity (endorsement by experts) was better for the M and S scale than for the EAAPS. The EAAPS showed superior reliability, the M and S scale better face validity, with comparable usability and other tests of validity.