Risk factors associated with stranger-directed aggression in domestic dogs

•Risk factors for stranger-directed aggression (SDA) were assessed via a questionnaire.•Reported fear of strangers was strongly associated with SDA.•Neutered males, mixed breeds, and dogs from pet stores had the greatest odds of SDA.•Severe SDA was highest in males and dogs with health problems, and lowest in sporting breeds.•Correlations in SDA within households indicate possible environmental and management effects. Aggression in dogs is a safety concern both for humans and animals, and can lead to decreased animal welfare in affected dogs due to potential abuse, neglect, relinquishment or euthanasia. We examined risk factors associated with stranger-directed aggression in dogs using the previously validated, Canine Behavioural Assessment and Research Questionnaire (C-BARQ). Results are based on participant reports of dog behaviour. Data were analyzed using mixed logistic regression, with participant ID and country as random effects. Dogs (n=14,310) were more likely to demonstrate stranger-directed aggression if the participant rated them as mildly or severely fearful of strangers, or mildly, but not severely, fearful in non-social situations, when compared to dogs with no fear. There was an interaction between sex and neuter status, with neutered males being more likely to be aggressive than any other group. Furthermore, adult dogs were more likely to be aggressive compared to adolescents or seniors, and dogs were less likely to be aggressive if acquired as an adult when compared to being acquired as a puppy or adolescent. The random effects for country and participant were significant (p