A systematic literature search to identify performance measure outcomes used in clinical studies of racehorses

BACKGROUND: Racing performance is often used as a measurable outcome variable in research studies investigating clinical diagnoses or interventions. However, the use of many different performance measures largely precludes conduct of meaningful comparative studies and, to date, those being used have not been collated. OBJECTIVES: To systematically review the veterinary scientific literature for the use of racing performance as a measurable outcome variable in clinical studies of racehorses, collate and identify those most popular, and identify their advantages and disadvantages. STUDY DESIGN: Systematic literature search. METHODS: The search criteria “((racing AND performance) AND (horses OR equidae))” were adapted for both MEDLINE and CAB Abstracts databases. Data were collected in standardised recording forms for binary, categorical and quantitative measures, and the use of performance indices. RESULTS: In total, 217 studies that described racing performance were identified, contributing 117 different performance measures. No one performance measure was used in all studies, despite 90.3% using more than one variable. Data regarding race starts and earnings were used most commonly, with 88.0% and 54.4% of studies including at least one measure of starts and earnings, respectively. Seventeen variables were used 10 times or more, with the top five comprising: ‘return to racing’, ‘number of starts’, ‘days to first start’, ‘earnings per period of time’ and ‘earnings per start’. MAIN LIMITATIONS: The search strategies may not have identified all relevant papers, introducing bias to the review. CONCLUSIONS: Performance indices have been developed to improve assessment of interventions; however, they are not widely adopted in the scientific literature. Use of the two most commonly identified measures, whether the horse returned to racing and number of starts over a defined period of time, would best facilitate future systematic reviews and meta‐analyses in advance of the development of a gold‐standard measure of race performance outcome.