"There is currently no accurate way to identify the number of dogs of a particular breed, and consequently no measure to determine which breeds are more likely to bite or kill."
"There are several reasons why it is not possible to calculate a bite rate for a breed or to compare rates between breeds. First, the breed of the biting dog may not be accurately recorded, and mixed-breed dogs are commonly described as if they were purebreds. Second, the actual number of bites that occur in a community is not known, especially if they did not result in serious injury. Third, the number of dogs of a particular breed or combination of breeds in a community is not known, because it is rare for all dogs in a community to be licensed, and existing licensing data is then incomplete. [Source: AVMA Task Force on Canine Aggression]When in doubt, call the CDC or the AVMA and ask.