How Many Dogs is Enough for Canine Science?

And does it matter which dogs they are?

Seven happy Australian Shepherd dogs - ever wondered how scientists decide how many dogs take part in a study?
Photo: Julia Remezova / Shutterstock

By Zazie Todd, PhD

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The number of dogs that take part in each research study is variable. Often, the sample size is small, because of the difficulty of recruiting dogs and their owners. And while scientists know how many are needed for statistical analysis, there are other things to take into account too.

For example, breed may or may not be relevant. If only ten dogs take part in a study and they are all Australian Shepherds, the results may not be the same as if they were all Cavalier King Charles Spaniels. 

There are 180 breeds recognized by the American Kennel Club. Studies can’t possibly include them all, and then there are mixed breeds to consider too.  Some researchers get round this by grouping dogs according to breed type (e.g. toy, working), and trying to include some of each. Scientific papers usually report the breed(s) of dog that took part, along with other variables that could potentially influence results, such as whether or not the dogs were neutered/spayed, their age and gender. 

Even within a breed, there may be differences in behaviour, as Lofgren et al’s recent study of show line and working line Labrador Retrievers found. (Incidentally, this study did a nice job of taking into account the fact that many pedigree dogs are related to each other).

Another consideration is whether the study requires interaction with strangers (i.e. experimenters), and training to teach the dog to operate some equipment or perform a particular behaviour. Dogs that are able to complete the training within the timescale of the study may not be typical of all dogs. There are often some drop-outs and some dogs that are too fearful to pass initial screening. 

The tasks can be complicated. For example, in McGowan et al’s (2014) brilliant study of the Eureka! effect, dogs were trained to perform specific actions with pieces of equipment, such as pressing a dog piano with a paw or pushing a box off a stack.  And in Berns et al’s (2012; 2014) ground-breaking MRI studies awake dogs voluntarily keep still during scans. The MRI dogs are highly-trained by definition, since they must take part in months of extensive training to be able to do the study. 

In other cases, dogs are surveyed in an environment that is natural to them, such as Ottenheimer Carrier et al’s research on dog parks, or Westgarth et al’s (2010) observations of dog walks. Here, they are studied when going about their normal daily life and engaging in normal behaviours.

Seven Cavalier King Charles Spaniels - is it a good sample for canine science?
Photo: Lenkadan / Shutterstock

Even though pet dogs are the focus of most research, other kinds of dogs are studied too, such as Savvides (2013) on street dogs in Bangkok. Then there are assistance dogs, therapy dogs, medical alert dogs (such as diabetes alert dogs (Rooney, Morant & Guest 2013)) and working dogs. Even with working dogs, there are striking differences: some live with their handler, while others live in kennels; assistance dogs must be used to people and an urban environment, sheepdogs not so much.

If we want to be able to say something about dogs in general, then all kinds of dogs need to take part in research. 

It’s different again for research on cats, since they are rarely accustomed to going places with their owners (except, perhaps, to the vet). An experiment in a lab will only be suitable for a special kind of pet cat. 

Even studies at the cat’s home will not work for all cats – most people know of a cat that runs and hides under the bed if someone new comes to the house.

The other thing to bear in mind is that our own experience with pets may not be the same as other’s. For example, some people take their dog for a walk every day, but others rarely if ever walk their dog (see e.g. Westgarth, Christley and Christian 2014). If we want to know about dogs and cats in general, all of these differences in lifestyle must be taken into account. 

So it’s not just a question of how many dogs (or cats) take part in a study, but also whether they are the right kind of dogs and cats. There are many things to balance when designing research. This is why so often we have to say ‘more research is needed’, as no one study can achieve the perfect design on all fronts. 

Do you think your dog or cat would like to take part in a research study?

Zazie Todd, PhD, is the award-winning author of Wag: The Science of Making Your Dog Happy and Purr: The Science of Making Your Cat Happy. She is the creator of the popular blog, Companion Animal Psychology, writes The Pawsitive Post premium newsletter, and also has a column at Psychology Today. Todd lives in Maple Ridge, BC, with her husband, one dog, and two cats. 

Useful links:

Berns, G., Brooks, A., & Spivak, M. (2014). Scent of the familiar: An fMRI study of canine brain responses to familiar and unfamiliar human and dog odors Behavioural Processes DOI: 10.1016/j.beproc.2014.02.011
Berns, G., Brooks, A., & Spivak, M. (2012). Functional MRI in Awake Unrestrained Dogs SSRN Electronic Journal DOI: 10.2139/ssrn.2047085  
Lofgren, S., Wiener, P., Blott, S., Sanchez-Molano, E., Woolliams, J., Clements, D., & Haskell, M. (2014). Management and personality in Labrador Retriever dogs Applied Animal Behaviour Science, 156, 44-53 DOI: 10.1016/j.applanim.2014.04.006  
McGowan, R., Rehn, T., Norling, Y., & Keeling, L. (2013). Positive affect and learning: exploring the “Eureka Effect” in dogs Animal Cognition, 17 (3), 577-587 DOI: 10.1007/s10071-013-0688-x  
Ottenheimer Carrier, L., Cyr, A., Anderson, R., & Walsh, C. (2013). Exploring the dog park: Relationships between social behaviours, personality and cortisol in companion dogs Applied Animal Behaviour Science, 146 (1-4), 96-106 DOI: 10.1016/j.applanim.2013.04.002  
Rooney NJ, Morant S, & Guest C (2013). Investigation into the value of trained glycaemia alert dogs to clients with type I diabetes. PloS one, 8 (8) PMID: 23950905  
Savvides, N. (2013). Living with dogs: Alternative animal practices in Bangkok, Thailand Animal Studies Journal, 2 (2), 28-50  
Westgarth, C., Christley, R., & Christian, H. (2014). How might we increase physical activity through dog walking?: A comprehensive review of dog walking correlates International Journal of Behavioral Nutrition and Physical Activity, 11 (1) DOI: 10.1186/1479-5868-11-83  
Westgarth, C., Christley, R., Pinchbeck, G., Gaskell, R., Dawson, S., & Bradshaw, J. (2010). Dog behaviour on walks and the effect of use of the leash Applied Animal Behaviour Science, 125 (1-2), 38-46 DOI: 10.1016/j.applanim.2010.03.007

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