Regardless of a canine’s actual breed, simply labeling a dog a “pit bull” can condemn it to a significantly longer stay in a shelter and make it less attractive to potential adopters, concludes a new study in PLOS One.

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Pit bulls are often stereotyped as aggressive and dangerous toward humans, though there is little evidence that those characteristics are inherent to the breed. The breed is popular among the dog fighting crowd, however, which contributes to its reputation for aggressiveness. To complicate matters, when attacks do occur, dogs may be labeled as pit bulls even when they are not. Indeed, in the United States, “pit bull” often serves as a catchall for a handful of breeds ranging from English bulldogs to American Staffordshire terriers; one person’s pit bull is another’s American bulldog mix.

This reputation follows the canines when they land in shelters. When potential adopters look at available dogs, they “don’t rate pit bulls any differently than look-alike dogs,” says the study’s lead author, Lisa Gunter, a graduate student in psychology at Arizona State University. “It’s only when we start attaching labels that people begin to perceive them more negatively.”

Most shelter dogs are of unknown origin, so employees often have to guess at an animal’s breed. Over a 10-year career working in shelters, Gunter noticed that she and her co-workers frequently arrived at different conclusions about a dog’s breed. And genetic studies have found significant discrepancies between descriptions of shelter dogs and their actual breed. One study found, for example, that half of the dogs that had been labeled as pit bulls at four Florida shelters had no pit bull ancestry in their DNA.

Gunter and her colleagues undertook a series of studies to find out how those potentially flawed labels might impact an animal’s chance of finding a home. They started by showing college students in California and users of the website Reddit photos of three dogs—a Labrador retriever, a pit bull-like dog and a border collie—without attached breed labels and asked questions about each, such as whether the dog looked smart or if the person would feel comfortable approaching it. The team found that participants ranked the pit bull-type dog as lowest on intelligence, friendliness, approachability and adoptability, and highest on aggressiveness and difficulty to train. When the pit bull appeared in a photo with an elderly woman or a child, however, it was rated more favorably.

Next, the researchers asked potential adopters at an Arizona shelter to rank dogs that appeared in photos and short videos on the animals’ approachability, intelligence, aggressiveness, friendliness, difficulty to train and adoptability. These scores were then summed to create an “attractiveness” composite for each pooch. To get around possible biases, such as apartment rules about animal sizes or bans on certain breeds, the team used phrases such as, “If circumstances allowed, I would consider adopting this dog,” to assess willingness to take a canine home.

When the dogs were not labeled as any particular breed, participants ranked pit bulls and look-alikes (dogs that were the same size and color as the pit bulls) as equally attractive. Potential adopters even ranked the pit bulls in video recordings as more attractive than the non-pit bull matches. When the researchers introduced breed labels, however, that trend reversed, with participants ranking the same dog as significantly less attractive than similar dogs without the label.

The researchers also found that pit bulls at that shelter waited over three times as long to find a home as their matched counterparts.

Finally, the team analyzed a set of data from an animal shelter in Florida that recently removed breed descriptions altogether. When freed from the loaded label, pit bull-like dogs were much more likely to find a home. Adoptions of these dogs increased by more than 70 percent, compared with the prior year, and the shelter’s euthanasia rate for the same group dropped by 12 percent, probably because more of them were finding homes.

Taken together, these results “are very convincing that breed labels negatively impact any dog that is labeled as ‘pit bull,’” says Erica Feuerbacher, who studies dogs at Carroll College in Montana and was not involved in the study. “Furthermore, we know from other studies that humans are quite bad at correctly labeling breeds, so many dogs could be erroneously labeled pit bull—even though they are not—and by that label they become less adoptable.”

Eliminating breed labels, which people seem to be using as poor proxies for stereotyped traits, may be the key to banishing a significant amount of dog discrimination—and getting more dogs into homes, Feuerbacher and the other researchers argue. There is also a need to devise better means of measuring dogs’ true personalities, including their potential for aggression, and of ensuring those assessments are valid not just in the shelter environment but also in homes, Gunter notes.

“We want to drive the adoption conversation toward evaluating whether an individual dog, regardless of the breed, is a suitable candidate for adoption,” she says. “Then we can match-make between the personality of the dog and that of the person, instead of just relying on labels.”