I disagree that pit bulls are one of the "worst" breeds. I do not like to see any breed stereotyped. As for Dr. Lachman, he is a psychologist, not a veterinarian, and I do not believe all of his ideas are well founded.
Dr. I. Lehr Brisbin of the University of Georgia wrote, "The few studies which have been conducted of the structure of the skulls, mandibles and teeth of pit bulls show that, in proportion to their size, their jaw structure and thus its inferred functional morphology, is no different than that of any breed of dog. There is absolutely no evidence for the existence of any kind of 'locking mechanism' unique to the structure of the jaw and/or teeth of the American Pit Bull Terrier."
In regard to claims of massive 1200 P.S.I., 1500 P.S.I., 1800 P.S.I. jaw strength he says, "To the best of our knowledge, there are no published scientific studies that would allow any meaningful comparision to be made of the biting power of various breeds of dogs. There are, moreover, compelling technical reasons why such data describing biting power in terms of 'pounds per square inch' can never be collected in a meaningful way. All figures describing biting power in such terms can be traced to either unfounded rumor or, in some cases, to newspaper articles with no foundation in factual data."
Many organizations are against breed specific legislation, including that which targets pit bulls, including the National Animal Control Association, Association of Pet Dog Trainers, American Kennel Club, the Society for the Prevention of Cruelty to Animals (SPCA), and the American Veterinary Medical Association.
In a 2011 study conducted in Spain and published in the Journal of Veterinary Behavior the researchers found that the larger the dog, the less likely it was to behave aggressively and that breeds typically identified as "dangerous" were no more likely to be aggressive than those not identified as dangerous.
In a study conducted at the University of Pennsylvania a few years ago the dachshund was the most aggressive dog, followed by the Chihuahua and the Jack Russell Terrier. While a Dachsund may do less damage than a larger dog, small dogs can still cause fatal injuries to babies and small children and they are probably more likely to bite, according to the Spain study.