Dangerous Dogs: Time for a Rethink?

Just because a dog is aggressive in one context doesn't mean they will be in another, according to research on the risk factors for aggression in dogs.

By Zazie Todd, PhD

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New research suggests it’s time to stop thinking of dogs as either ‘safe’ or ‘dangerous’. In most cases canine aggression seems to be a learned response to a particular situation, not a personality characteristic, since a dog that growls or bites in one situation may not do so in other contexts.
A large survey in the UK (Rachel Casey et al, University of Bristol) investigates canine aggression towards family members, towards unfamiliar people in the house, and to unfamiliar people outside. The researchers described aggression as “barking, lunging, growling or biting.” Thus the survey incorporated a range of behaviours that are considered aggressive, instead of just looking at biting.
A dog that bites in one situation is not necessarily a threat in other situations, research shows. Photo shows funny dog biting sign.
Photo: chingyunsong / Shutterstock

A total of 3897 questionnaires were completed out of 14,566 that were distributed to dog owners. The average age of dogs was 4 years old, with a range from 6 months to 17 years. 

Aggression towards family members was reported by 3% of dog owners. 7% reported aggression towards unfamiliar people coming into the house, and 5% towards unfamiliar people out and about. Hiding or avoiding family members was reported by 4% of owners; hiding or avoiding unfamiliar people was more common at 10%.

One of the most interesting findings is that the three different contexts in which aggression occurred did not seem to be related. For example, a dog that was aggressive towards family members was typically not aggressive to unfamiliar people, whether in the home or outside. This suggests we should reconsider how we think of dangerous dogs. 

Lead author Dr. Rachel Casey says, “Dog owners and members of the public need to be aware that any dog could potentially show aggression if it is anxious or feels threatened, even when it has never done so before. On the other hand, dogs which have shown aggressive signs in one situation are not necessarily ‘dangerous’ when in other contexts – an important consideration in the assessment of animals, such as in rehoming centres.”

Puppy classes had a protective effect. Dogs that had attended puppy class before the age of 12 weeks were significantly less likely to be aggressive towards unfamiliar people in the home or outside. Attendance at obedience classes, however, was a risk factor: dogs that had been to obedience class were more likely to be aggressive towards family members. It could be that people are more likely to take their dog to such a class if it is already showing aggression, or it could be related to the training method that was used.

Owner’s choice of training method was important. The use of positive punishment or negative reinforcement was a risk factor for aggression towards family members or unfamiliar people outside. In everyday language, these are punishment-based training approaches (for a fuller explanation of the technical terms, see this post and video by Eileen Anderson). 

Other surveys have also shown that the use of punishment-based training is linked to increased owner-reported behaviour problems (Hiby et al 2004; Herron et al 2009; Rooney and Cowan 2011). Blackwell et al (2008) found that owners who used only positive reinforcement were significantly less likely to report problems with attention-seeking, aggression or fear in their dogs, whilst those who used positive punishment were more likely to say their dogs were aggressive or fearful. Arhant et al (2010) found that a greater frequency of punishment was associated with more aggression and excitability in dogs, while higher frequency of rewards correlated with higher obedience.

These results are correlations, and do not prove causality. For example, it could be that people are more punishing towards their dogs because the dog misbehaves. However, it is possible that using these methods causes increased aggression. Further research on this topic is needed.

Dogs obtained from rehoming centres were more likely to show aggression towards owners, as were those obtained from ‘other’ sources (mainly pet shops and internet sites). The major UK rehoming charities work hard to rehabilitate dogs in their care, but aggression to an owner is difficult to assess in a kennel and may also be the reason a dog was initially given up. This result is also different from Blackwell et al (2008) who found that dogs from rescue centres were no more likely to be aggressive, fearful or attention-seeking than those from other sources.

It’s worth noting that dogs from re-homing centres were not more likely to be aggressive to unfamiliar people, showing the effectiveness of behavioural assessments and rehabilitation for this.

There are some other interesting results. Aggression towards unfamiliar people inside or outside the home increased with the dog’s age. Female spayed dogs were less likely to be aggressive in the three different contexts, but for male dogs there was no effect of neutering, in contrast to other studies. Dogs belonging to older owners were less likely to show aggression to the owner or an unfamiliar person in the home. The gender of the owner did not have an effect, except that women were less likely to report aggression to unfamiliar people entering the home.

The researchers also tested the effects of breed group compared to crossbreed dogs. Aggression to unfamiliar people entering the house was less likely amongst Labradors, Golden Retrievers, Cocker Spaniels, Springer Spaniels, other types of retriever, Setters, many types of Terrier and Boxers. No breeds had an increased risk of aggression in this context. Aggression to unfamiliar people outside the house was more common amongst German Shepherds and Belgian Shepherds compared to crossbreeds. Breed had no effect on the risk of aggression to family members.

The scientists say, “it is important to note that these [breed group differences] account for only a very small proportion of variance between groups. In other words, although breed seems to be a contributing factor influencing risk, other factors have a much greater influence.”

The questionnaire results may not be representative of the UK population, since it was not a randomized sample. Nonetheless this valuable study has important consequences for the welfare of both dogs and humans, and will hopefully lead to a better understanding of the factors that cause canine aggression to people.  As well as finding that aggression is often context-specific, it is a reminder that any dog can bite. It’s hard to think of our best friends as potentially nasty, but instead of thinking of dogs as either ‘safe’ or ‘dangerous’, a more nuanced approach is needed. 

You can read Dr. Rachel Casey’s blog about the study here.

If you liked this post, check out my book Wag: The Science of Making Your Dog Happy. Modern Dog magazine calls it "The must-have guide to improving your dog's life."
Has your dog ever shown aggression and, if so, in what context?

Arhant, C., Bubna-Littitz, H., Bartels, A., Futschik, A., & Troxler, J. (2010). Behaviour of smaller and larger dogs: Effects of training methods, inconsistency of owner behaviour and level of engagement in activities with the dog. Applied Animal Behaviour Science, 123(3-4), 131-142.
Blackwell, E. J., Twells, C., Seawright, A., & Casey, R. A. (2008). The relationship between training methods and the occurrence of behavior problems, as reported by owners, in a population of domestic dogs. Journal of Veterinary Behavior, 3(5), 207-217.
Casey, R. A., Loftus, B., Bolster, C., Richards, G. J., & Blackwell, E. J. (2014). Human directed aggression in domestic dogs (Canis familiaris): Occurrence in different contexts and risk factors. Applied Animal Behaviour Science, 152, 52-63.
Herron, M. E., Shofer, F. S., & Reisner, I. R. (2009). Survey of the use and outcome of confrontational and non-confrontational training methods in client-owned dogs showing undesired behaviors. Applied Animal Behaviour Science, 117(1-2), 47-54.
Hiby, E. F., Rooney, N. J., & Bradshaw, J. W. S. (2004). Dog training methods: their use, effectiveness and interaction with behaviour and welfare. Animal welfare, 13(1), 63-69.
Rooney, N. J., & Cowan, S. (2011). Training methods and owner–dog interactions: Links with dog behaviour and learning ability. Applied Animal Behaviour Science, 132(3-4), 169-177.

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