A limited number of studies have been performed on the number of human deaths due to bite trauma caused by dogs, and have generally surveyed news media stories for reports of dog bite-related fatalities. This methodology is subject to several potential sources of error: some fatal attacks may not have been reported; a study might not find all of the relevant news reports; and the potential for misidentification of dog breeds, although courts in the United States and Canada have ruled that expert identification, when using published breed standards, is sufficient for the enforcement of breed-specific legislation. It is possible to distinguish dogs by breed using DNA testing,but test results for any one dog can vary widely depending upon the laboratory that performs the test and the number of purebred dog breeds in the laboratory's DNA database.
