A study performed by Equibase at the request of the Thoroughbred Owners and Breeders Association (TOBA) indicates the percentage of "career-ending did-not-finish" (CEDNF) incidents was about twice as high on dirt than synthetic surfaces in 2009.

The study is based on a review of official racing charts. The "CEDNF" statistics, as they are called, are for horses that didn't finish their last races in 2009 and didn’t yet return to work out or start in 2010.

Last year, 0.39% of CEDNFs came on dirt (percentage per starter), 0.19% on synthetics, and 0.26% on turf. Overall, the percentage of CEDNFs in 2009 was 0.35% (or 35 starters per 1,000), the same as it was in 2008, according to the report.

The report also looks at categories such as racehorse age, surface condition, and individual tracks