I don't see a cite for that.
“U.S. Population / Fatal Dog Attacks
Year Human Population Dog Population # Fatal Dog Attacks
1950 151 million 20-22 million 10
1970 203 million 31 million 12
1980 226 million 40 million 15
2000 281 million 60+ million 19 “
Taken from http://www.nationalcanineresearchcouncil.com/historicCases.asp
“Some places, such as Oakland, CA, report that more “pit bulls” are registered with the city than any other breed. A few studies estimate that U.S. shelter “pit bull” populations reach 33% on average, and up to 50% or more in larger cities.”
taken from http://www.happypitbull.com/basics/myths.html#10
If you look at the number of dogs in the United States, it is approximately at 70 million right now. Pit bull-type dogs are very prevalent, especially in big cities, but are being seen pretty much everywhere now. Irresponsible breeders are the cause, and their population is still increasing. The UKC lists the American Pit Bull Terrier as the #2 most registered breed, and that is just one registry. That doesn’t include AKC American Staffordshire Terriers, English Staffordshire Bull Terriers, and unregistered pit bull-type dogs, as well as other purebred, registered dogs which are commonly mistaken for pit bulls.
http://www.ukcdogs.com/WebSite.nsf/WebPages/LrnTop10
This shows that the pit bull-type is one of the most popular types of dogs right now, and since there are about 70 million dogs, we can safely assume that pit bull-types represent at least 20% of large dogs (and that is underestimating big time). 20 percent of 70 million is about 14 million dogs. Let’s say that on average right now, there are 26 pit bull-type dogs that have taken a human life. That’s 1.857% of their population that has killed a person, and 98.143% that haven’t.
Take the population of dogs in 2000 when the above study was done. There were 19 human fatalities caused by dogs that year, and about 60 million dogs. That equates to 3.16% of dogs of any breed that were responsible for human deaths.