A comparison of survival models for assessing risk of racehorse fatality.
Abstract: Survival analysis was used to assess risk factors for fatal injuries on UK race courses. This allowed assessment of variation due to temporal horse-level effects, including previous racing intensity and historical distribution of race types, as well as race-level factors. Comparisons were made between measuring survival time as number of days and as number of races to injury from the first race. Two related models were presented for time as number of races to injury: a Cox regression model fitted using partial likelihood, with the Efron approximation to handling ties, and a discrete-time logit model fitted using maximum likelihood. The latter approach had the advantages of being computationally more efficient and enabling the testing of different functional forms for the dependence of hazard on time. Retrospective data were available from all race starts on the 59 courses in Britain from 1990 to the end of 1999, as analysed by . The analysis was conducted on the data for the 47,424 horses that had started racing in the UK: 538,895 starts with 1,228 fatal injuries. Horses starting racing abroad were excluded, but some included horses would have raced abroad at some stage during their racing career. The results for the selected models were broadly consistent with each other and with previously published studies. Steeplechase and hurdle races had a higher risk of fatal injury than flat races (relative hazards 1.5 and 1.7, respectively). Risk increased with the firmness of surface, age and race distance (reaching a plateau at 20 furlongs) and decreased with previous racing intensity (reaching a plateau after seven races run in the last 12 months). Horses running their first race of a new type were also found to be at higher risk (relative hazard 1.5). The main difference between the models for time as number of days and number of races concerned the role of age: age at race was identified as the more important factor in the latter model, whereas, age at first race was more significant in the former model.
Publication Date: 2006-03-20 PubMed ID: 16546277DOI: 10.1016/j.prevetmed.2006.01.003Google Scholar: Lookup
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- Journal Article
- Research Support
- Non-U.S. Gov't
Summary
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This research work used survival analysis to study risk factors associated with fatal injuries of racehorses in the UK, comparing different survival models including racing intensity and types of races. Further, the study utilizes two different measurements: number of days from the first race and number of races until injury. The two proposed models connected to the number of races to injury provide efficient computational strategy and enables testing of various risk associations over time.
Study Model and Data
- The research utilized a Cox regression model and a discrete-time logit model. The Cox model was fitted partially with likelihood using an Efron approximation for handling ties, while the discrete-time logit model was fitted with maximum likelihood.
- The logit model provided improved computational efficiency and enabled checking various functional forms concerning hazard timings.
- Data used in the study were retrospective and derived from all race starts on the 59 courses in Britain from 1990-1999. The data acquisition didn’t include horses that started their racing career abroad.
- The data included a total of 47,424 horses that started their racing career in the UK, accounting for 538,895 starts and 1,228 fatal injuries.
Findings and Observations
- Comparative results from the chosen models corroborated each other and agreed with previously published studies, thereby strengthening the findings.
- It was found that hurdle races and steeplechase presented a higher risk of fatal injury when compared to flat races with relative risks of 1.7 and 1.5, respectively.
- Other factors that showed increased risk included the hardness of the ground, age of the horse, and race distance, with the risk levelling out at 20 furlongs.
- Conversely, the risk decreased with greater racing intensity, reaching a plateau after seven races run within 12 months.
- Horses participating in a new type of race for the first time also exhibited an increased risk of fatal injury (relative hazard of 1.5).
Differences between the Models
- The main divergence between the time models (number of days and number of races) was noted for the factor of age.
- Where the model using number of races identified the age of the horse at the race as more significant, the model using number of days highlighted the age of the horse at the first race.
Cite This Article
APA
Henley WE, Rogers K, Harkins L, Wood JL.
(2006).
A comparison of survival models for assessing risk of racehorse fatality.
Prev Vet Med, 74(1), 3-20.
https://doi.org/10.1016/j.prevetmed.2006.01.003 Publication
Researcher Affiliations
- Animal Health Trust, Lanwades Park, Kentford, Newmarket, Suffolk CB8 7UU, UK. william.henley@aht.org.uk
MeSH Terms
- Age Factors
- Animals
- Athletic Injuries / epidemiology
- Athletic Injuries / mortality
- Athletic Injuries / veterinary
- Female
- Fractures, Bone / epidemiology
- Fractures, Bone / mortality
- Fractures, Bone / veterinary
- Horses / injuries
- Likelihood Functions
- Male
- Physical Conditioning, Animal / adverse effects
- Proportional Hazards Models
- Retrospective Studies
- Risk Factors
- Running / injuries
- Sports
- Survival Analysis
- Time Factors
- United Kingdom
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