Researchers at the University of Sao Paulo studied 665 pet dogs from 57 breeds, all varying in size.

The owners of the dogs completed an online questionnaire relating to themselves, their dog’s characteristics and another on the aggressive tendencies of the dogs, such as parking or attacking.

The results found that heavier dogs were considered better well-behaved and less aggressive by their owners.

Researchers also discovered that for every one kilogram of body mass a dog had, its aggressive behaviour decreased by three percent.

Small dogs with short snouts, such as brachycephalic dogs such as Pugs and Bulldogs, were considered the most aggressive.

“Aggressiveness toward the owner was 79% more likely among brachycephalic than mesocephalic dogs,” said Flavio Ayrosa, first author of the study.

Golden Retrievers, Beagles and Labradors, with more intermediate skulls, are considered as mesocephalic breeds.

While researchers found cause-and-effect with the findings, Ayrosa said it is not possible to know which comes first; the dog’s behaviours or their environment.

“In the case of the factor "walking the dog", for example, it may be that people walked their dog less because the animal was aggressive, or the dog may have become aggressive because the owner didn't take it out enough,” he said.

“Traits such as weight, height, cranial morphology, sex and age influence the interaction between dogs and their environment.” Researchers hope the findings will help owners understand that a dog’s aggressive tendencies are a result of the pet and its environment, and not just the animal itself.

“The environment and the owner-pet relationship, as well as morphology, are all factors that influence how pets interact with us and how we interact with them,” said Professor Briseida de Resende, an author of the study.