Verified by 
One of the most important behavioral issues associated with dogs concerns aggression, especially when that aggression is directed towards people. A recent study finds a number of factors that can be used to predict which dogs are most likely to be aggressive and also tries to indicate what the situations are where the aggression occurs. This research was reported in the journal Applied Animal Behaviour Science by Rachel Casey, Bethany Loftus, Christine Bolster, Gemma Richards and Emily Blackwell of the School of Veterinary Science at the University of Bristol*. It is a huge study, involving 3897 dog owners from the UK, and it looks at a large number of different variables that influence the risk that dogs will show aggressive behavior. While many of the results are interesting and potentially useful, it is likely that the very few people, other than some dedicated scientists, will ever read it. This is because of the complex statistical analyses involving things like multivariable logistic regressions, as well as the absence of simple tables with arithmetic averages or percentages which might make the findings accessible to an average reader. Still, because some of the findings are important, I will try to dig out a few of the highlights of this research for you.
The data collection involved questionnaires that were given out at variety of different places including veterinary practices, dog shows, agricultural and horse events, pet shops or directly to people encountered while walking their dogs. The aim of the study was to estimate the number of dogs showing aggression towards people in three different settings. The first involved unfamiliar people entering the dog's home, the second dealt with meeting unfamiliar people outside of the home, and the third involved aggression toward family members. Previous studies of dog aggression have usually been based upon actual dog bites incidents, which obviously represent the highest level of aggression. This study tried to capture a broader variety of aggressive behaviors including those of lower intensity. Thus the dog owners were asked if their dogs ever barked, lunged, growled, or attempted to bite a person as well as whether this behavior is a continuing problem.
The first finding of interest was that many dogs only showed their aggressive tendencies in one or another of the three situations. This goes against the common public perception that aggression is a personality trait of an individual and that particular dogs are either always "perfectly safe" or always "vicious".
Another important finding is that the rates of aggression are quite low. Thus, over the lifetime of the dog, only about 3% of owners reported aggression toward family members, 7% reported aggression towards unfamiliar people entering the house and 5% reported aggression to unfamiliar people when out of the house. This is a remarkably low frequency since the criterion by which dogs were classified as "aggressive" or "not aggressive" in this study was whether owners reported any aggressive behaviors at all—ever. This means that dogs defined as ‘aggressive’ here included those which might have growled once in an atypical situation not just those who frequently display severe aggression towards many people or in a variety of situations.
For now, let's focus on the data about aggression toward unfamiliar people. Because of the amount of research and public concern associated with the issue of whether some dog breeds are more aggressive than others (click here or click here for examples) these researchers addressed the question by comparing the rates of aggression of dogs of known breeds with a random sample of mixed breed dogs assessed by their survey. While there is no space here to go through all of the breed and breed group findings, one is of particular interest. It turns out that some breeds are significantly less aggressive toward unfamiliar people entering their house and these include: Labrador Retrievers, Golden Retrievers, Cocker Spaniels, Springer Spaniels, and other retrievers (including Chesapeake Bay Retrievers, Curly Coated Retrievers, Flat Coated Retrievers and Nova Scotia Duck Tolling Retrievers). Also low in aggression were the Setters (including English Setters, Gordon Setters, Irish Setters as well as Irish Red and White Setters). Contrary to other research showing that the Pit Bull-Type Terriers are generally higher in aggression, this was not confirmed in this present research, on the other hand a number of other terriers were significantly lower in aggression towards people then the mixed breed reference group (including Airedales, Bedlington Terriers, Cairn Terriers, Cesky Terriers, Fox Terriers, Wirehaired Fox Terriers, Glen of Imaal Terriers, Irish Terriers, Norfolk Terriers, Kerry Blue Terriers, Lakeland Terriers, Manchester Terriers, Welsh Terriers, Norwich Terriers, Scottish Terriers, and Soft Coated Wheaten terriers). Finally we can add Boxers to the list breed showing low aggression toward visiting strangers.
In this particular data set increased aggression toward unfamiliar people outside of the house was found only for German and Belgian Shepherds when compared to the cross-breed group.
One very interesting finding concerned the positive effects of puppy socialization classes. According to these data such classes seem to impart a protective effect against aggression. Attending puppy classes on at least two occasions before the dog was 12 weeks of age was associated with a 1.4 times reduced risk of aggression toward unfamiliar people entering the house and a 1.6 times reduced risk of showing aggression to unfamiliar people out of the house.
While on the issue of dog training, one of the most practically significant findings found in this research has to do with the effect that the type of training has on a dog's risk of aggression. There have been a number of studies that have reported that training procedures based on punishment can have negative consequences (click here for an example). In this study the researchers defined such punitive training techniques as including things like physical punishment (hitting the dog), verbal punishment (shouting), electrical or citronella collars, choke chains and jerking on the leash, prong collars, water pistols, electric fences and so forth. Such punitive techniques apparently increase the risk of aggression in dogs. They are associated with a 2.9 times increased risk of aggression to family members, and a 2.2 times increased risk of aggression to unfamiliar people outside of the household.
I have only briefly touched on some of the results from this complex study, however the data makes it clear that training methods, breed, and puppy socialization classes have significant effects on the risk of dogs showing aggressive behaviors toward people.
Stanley Coren is the author of many books including: The Wisdom of Dogs; Do Dogs Dream? Born to Bark; The Modern Dog; Why Do Dogs Have Wet Noses? The Pawprints of History; How Dogs Think; How To Speak Dog; Why We Love the Dogs We Do; What Do Dogs Know? The Intelligence of Dogs; Why Does My Dog Act That Way? Understanding Dogs for Dummies; Sleep Thieves; The Left-hander Syndrome
Copyright SC Psychological Enterprises Ltd. May not be reprinted or reposted without permission
* Data reported here is from: Rachel A. Casey, Bethany Loftus, Christine Bolster, Gemma J. Richards, Emily J. Blackwell (2014).Human directed aggression in domestic dogs (Canis familiaris): Occurrence in different contexts and risk factors. Applied Animal Behaviour Science, 152, 52– 63
