Title: Human directed aggression in domestic dogs (Canis familiaris): Occurrence in different contexts and risk factors
Authors: Rachel A. Casey, Bethany Loftus, Christine Bolster, Gemma J. Richards, Emily J. Blackwell
Published: December 11, 2013 in Applied Animal Behaviour Science
These researchers distributed 14,566 surveys and received 3897 completed, legible responses (26.6% response rate). The surveys assessed owner demographics, basic info about the owner’s youngest dog (origin, age, breed, neuter status) as well as training methods (grouped into positive reinforcement/negative punishment or positive punishment/negative reinforcement) and instances of human directed aggression or avoidance of humans in multiple contexts. The researchers used their survey results to create three multivariate models for aggression directed towards family members, towards unfamiliar people entering the home and towards unfamiliar people outside of the home.
[Brief explanation of multivariate models: In this case, this means that the authors took all of the questions they asked about in the surveys and entered them into a statistical model as variables, such as “breed type”, “age”, “neuter status”, etc. These variables were assessed for their ability to predict an outcome variable, which were the aggressive responses in various contexts from the surveys for this research. Using exclusion criteria, variables are eliminated if they didn’t predict the outcome variable very well. The final model contains only those variables that, in combination, predict the outcome variable “well”, according to various statistical standards. For more information, see this NIH article on multivariate analysis.]
The model with the outcome variable of aggression directed towards family members included owner age, dog age and neuter status, training method, attendance to training classes (except puppy classes), breed type and origin of dog. The model with aggression directed at unfamiliar humans entering the household included owner gender, owner age, dog age and neuter status, attendance to puppy classes and breed type. Finally, the model with aggression directed at unfamiliar humans outside the household included dog age and neuter status, puppy classes, ring craft classes, training category and breed type.
Let’s start with my complaints about this article. I felt “aggression”, as assessed through the surveys, was again poorly defined. The authors briefly acknowledged that there may be discrepancies between owner interpretation of dog behavior but seemed to feel that differences might be gender based. I’m not sure how substantiated this theory is, but this issue could be circumvented by clearly defining “aggressive” behaviors in a certain way. Obviously, recall (a respondent’s imperfect memory) and reporting (a respondent’s voluntary suppression of information) biases will still exist but these are issues inherent with surveys.
Although the authors clearly define their study population as a convenience sample, I didn’t think this was appropriately included in the interpretation of the results. Half of the respondents had received this survey at a dog show or dog-related event, which is very unrepresentative of the general dog-owning population in my personal experience. I’m not sure if wide-scale dog owner demographics are available but I feel like the inclusion of so many people who were motivated to attend a dog show makes the generalizability of this study to the general population of dogs and owners is questionable.
My final critique is the interpretation of owner gender, owner age, dog gender/neuter status and dog breed variables in the final multivariate models. The authors did a nice job of comparing their results with previous studies but for these variables in particular, the discussion got confusing. It basically came down to the fact that previous studies have both agreed and disagreed with the results from this research for these particular factors. So do these variables contribute to a dog’s risk of human direct aggression, and why is that? The authors just sort of shrugged in answer. I’m all for being open and honest about your findings, but…really? That’s about half of the final variables in all three models! If there really isn’t anything you can conclude from these variables except that more research needs to be conducted into each of these variables, why were they included to begin with?
Finally, the interesting bits of the study. First, there was the origin of the dog. Compared to dogs obtained from breeders, dogs from rescue groups had a 2.6 times increased risk of aggression towards humans and dogs obtained from an “other” source (pet stores, internet sites, etc.) had a 1.8 times increased risk. Are shelter dogs at greater risk of human directed aggression? There are two potential explanations to this apparent finding:
1. Yes, shelter dogs have an increased risk of human directed aggression because A) human-aggressive dogs are more likely to surrendered to a shelter and/or B) being in a shelter could somehow make a dog more aggressive towards humans.
2. No, shelter dogs are not actually more likely to exhibit human directed aggression but it appeared in this study as the result of owners of dogs from rescue centers being more likely to report human directed aggression because A) they may feel less “responsible” for the dog’s behavior since (in most cases) they aren’t the first owner (i.e. less reporting bias than owners who obtained their dogs from a breeder) and/or B) they may be more attuned to their dog’s behavior because of its unknown background (i.e. less recall bias than owners who obtained their dogs from a breeder).
So which is it? I have no idea – I suspect it’s a combination – and I wish the authors’ had delved into this finding a little more. Or maybe someone could pay me to do that!
Next, the authors found that dogs that were aggressive in one context were not likely to show aggression in another context. This is really interesting finding because it supports what all those behaviorists have been harping about (that dogs exhibit aggressive behavior in response to certain perceived threats in certain contexts) and goes against the popular theory that some dogs are “vicious” while other dogs are “perfectly safe.” These researchers furthermore added that their finding that pit bull-type breeds (Staffordshire Bull terriers, other bull breeds and mastiff breeds) that are frequently deemed vicious by popular culture and breed-specific legislation did not have an increased risk of human directed aggression compared to the baseline group (cross breeds).
Attendance to training classes (except puppy classes) was associated with an increased risk of human directed aggression in this study. The authors concluded that this could be because A) these classes somehow increased dogs’ aggressive behavior or that B) owners with dogs who exhibited human directed aggression were more likely to take them to training classes. Additionally, I think there could be an increased awareness of dog behavior in owners who have been instructed by a qualified dog trainer.
In a somewhat related vein, this study also found that certain training methods were associated with an increased risk of human directed aggression. Dogs of owners who reported using any kind of positive punishment or negative reinforcement had a 2.2 increased risk of aggression direct at unfamiliar people outside the household and a 2.9 increased risk of family directed aggression. The relationship of factors is unknown: A) do owners with aggressive dogs “resort to” punitive training methods more often or B) do dogs trained with punitive measures develop aggressive behaviors more often?
A small note of my own personal opinion: it would be useful to know if shelter dogs are actually more likely to demonstrate human directed aggression. Why?
- Human directed aggression from dogs puts the humans around them at risk of being bitten, which could result in psychological trauma, serious injury or even death.
- Aggressive dogs aren’t happy dogs. Behaviorists tend to think that dogs exhibiting aggressive behavior are fearful and anxious.
- If aggressive behaviors are being exhibited in a limited number of contexts, they could possibly be resolved with fairly minimal behavior modification* or management. Small(ish) effort = happier dog + safer humans. That seems like a good deal to me!
- Rescue groups try their darnedest to send their adopters home with as much information as they need to succeed with their new family addition. If dogs from shelters really are more likely to demonstrate human directed aggression, adopters ought to be prepared for it!
- If dogs from rescue centers really aren’t more likely to exhibit human directed aggression and it’s really that owners who got their dogs from breeders are unaware of or unwilling to admit to their dog’s aggressive behavior, this also needs to be addressed. Reading a dog’s warning signals can keep dogs happier and humans safer!
*Owners of dogs exhibiting any kind of aggressive, territorial or otherwise concerning behaviors should seek the help of a trained veterinary behaviorist or certified animal behaviorist before attempting any kind of behavioral modification!