The American Dog Breeders Association describes purebred American Pit Bull Terriers as athletic, heavy dogs that do not stray into bulkiness with defined and smooth musculature. The head must be in proportion to the body with a neck long enough to seat the head above the top of the back when upright. They must be socialized and gentle without displaying signs of aggression or timidity.
Pit bulls are typically well socialized, so unruly behavior or aggressiveness may indicate that a dog is not of a pure pedigree. The proportions are also an important factor in determining if a dog is purebred.
If no pedigree is available, breed is determined by appearance, but pit bulls are difficult to categorize because the word refers to over 20 breeds, not including those that are mixed with Boston terriers, French bulldogs and English bulldogs. Because of this ambiguity, some breeders and researchers criticize the unreliability of visual markers for identifying breed.
An alternative to visual identification is DNA analysis. The documented accuracy rate for DNA identification is much higher, averaging 90 percent. Another important factor in the improved accuracy rate of DNA analysis is that many animal control officers and veterinarians are not trained in breed identification. Some states and buildings prohibit the ownership of pit bulls.