Some dog bite statistics include the fact that pit bulls and related breeds lead the pack in most dog attacks in the United States and Canada, and that chow chows, despite being rather uncommon, are implicated in a disproportionate number of attacks. German Shepherds also often lead dog attack statistics.
There have been many studies done that track bite statistics by breed, including one that compiled news reports of attacks in the U.S. and Canada for the years 1982 through 2014. In this study, compiled by Merrit Clifton, pit bulls were implicated in a very large number of attacks, such that even if many of the dogs were misidentified by the press, they would still top the list of most aggressive breeds.
In a literature review of studies by the American Veterinary Medical Association, German Shepherds, pit bulls and small sporting breeds, including Spaniels, were among the most prone to bite.
Both this literature review and Clifton's study point to chow chows being particularly aggressive despite their small presence in the pet population. In Clifton's study, chow chows made up less than one percent of all dogs, yet ranked ninth in number of attacks.