Wednesday, 10 August 2016

Dog Bite Strength: It's Not What You Think

Scientists tracked down the evidence for a common statement about bite strength in dogs – and found it lacking.

A happy pit bull surrounded by flowers

Have you ever read comments about the strength of a dog’s jaw when it bites? These statements are often made in relation to certain types of dog, like pit bulls. Maybe some people take it as fact. But what if it’s not true?

A recent paper by Dr. Gary Patronek (Cummings School of Veterinary Medicine, Tufts University) et al traced citations in the literature and went back to the original sources to investigate the truth of the published statements. They say they chose the literature on the strength with which a dog can bite for several reasons, including that this is a salient figure that jumps out at people and is remembered, and that the literature was large enough and easy to assess for accuracy.

They picked a topic on which people have been sceptical for some time. Writing on his blog in 2010, Stanley Coren PhD said,

“Let’s put these numbers into a meaningful context. Imagine a bite force of 2000 pounds. To achieve this, suppose that we had a dog’s jaw and wanted to press the upper portion down with this force, it would require our putting a pressure equivalent to the weight of a subcompact automobile (like a smaller Toyota or Hyundai) on the top jaw. That simply did not make sense.” 

In fact a Smart Fortwo weighs 1808 lbs, and a Mitsubishi Mirage is 1,973lbs. So those are the cars we can think of if we’re going to use Dr. Coren’s analogy.

Patronek et al wanted to know what the evidence is for this. They looked at papers from 1969 – 2009, and two court cases, that referred to canine bite strength. They went through the literature to trace the statements back to the origin. So what did they find?

“We tracked each citation to 1 of 7 original sources,” they write, “and did not find verifiable evidence (or data obtained from a controlled experiment) about bite force in any of the articles. In 2 of the original sources, statements about bite force were found, but there were neither data nor a citation to support those statements. In 4 other original sources, none contained any statement or data about bite force, despite being cited by other scientific articles as though they had. The final original source was not a scientific article at all, but a newspaper article that again provided no source for the data presented.”  [references omitted for ease of reading – see link below]

In other words, there is no evidence for the statement that a pit bull, or any other kind of dog, has a bite strength of 1800 or even 2000 PSI.

A happy pit bull puppy in the flowers
For scientists, this is a reminder to be careful to verify sources. Patronek et al are not suggesting anyone has deliberately misled – rather, that mistakes have been made, and over successive papers by different authors, they have been amplified. These days, with more articles available electronically, it is easier than ever to verify original sources (although no university library will have everything).

A particular problem is what they call ‘daisy-chaining’ – basically the use of secondary sources (rather than the original) and not being clear when information is from the introduction section rather than actual results.

At other times, however, they say it’s hard to know why these mistakes occurred.

“Four articles specifically claim that the bite force of a “pit bull” type dog can be as much as 1,800 pounds per square inch. There is not a single original source reporting a Result that substantiates this claim. And what are we to make of cases where a source that literally did not contain any information about bite force was cited.” [references omitted]

I find it interesting that the four articles referring to a pit bull bite strength of 1,800 PSI (and indeed almost all of the papers making comments about bite strength) are from the medical literature, not from journals on animal behaviour or biology.

Patronek et al point out there are consequences to this, not just for the scientific literature but also real life (as in the court cases they studied).

More generally, we can consider what if people are afraid of certain dogs because they’ve been erroneously told about this supposed enormous bite strength? What if people cite this information in support of breed specific legislation, even though it's wrong?

Preventing dog bites is complicated. Breed specific legislation isn't the answer because any dog can bite. Fortunately fatal dog attacks are incredibly rare and involve many factors that could potentially be prevented. Programmes to educate children about dog bites work to reduce risky behaviour around dogs. Better education for adults on dogs and canine behaviour can help too. But approaches to dog bite prevention also need to take into account that many people think ‘it won’t happen to me’ and so may not pay attention to information about dogs in general, or to their dog’s behaviour in the moment.

Patronek et al’s paper shows a commonly-held belief about certain types of dog is wrong. Flawed research write-ups have given pit bulls and other dogs a bad name, and it’s important to set the record straight.

The paper is open access and you can read it at the link below. There is a handy diagram if you want to follow the faulty references back.

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Patronek, G., Bradley, J., & Cleary, D. (2016). Who is minding the bibliography? Daisy chaining, dropped leads, and other bad behavior using examples from the dog bite literature Journal of Veterinary Behavior: Clinical Applications and Research, 14, 17-19 DOI: 10.1016/j.jveb.2016.06.004
Photos: Matthew Lyon (top) and Zuzule (both


  1. Shame that this article does not include any facts on the actual bite pressure, otherwise an excellent article

    1. I actually don't know for sure for a live dog. If you follow the link to Stanley Coren's article, you will find an answer based on a study that gave estimates between 170 pounds and 568 pounds for a German Shepherd Dog, depending on which part of the jaw is involved. This is from a study that used electrical stimulation of the jaws of anaesthetized dogs, and looked at the jaw structure of dead dogs. His post is an interesting read and also includes estimates from a National Geographic Show and for different types of animals too. 120 pounds is the estimate for a human. Of course we also have to remember that dogs have a lot of control over their jaws and hopefully as puppies they learn a very good acquired bite inhibition.

  2. Excellent. I do thoroughly enjoy the Internet. Where else would I have found you and your MOST interesting discovery?!? Sadly, I am one who bought the BS.
    I love it when I'm stupid and wrong.
    Thank you from Canada's Rocky Mountains.

  3. Good stuff !

    As well as the lack of actual measurements for dogs there is also widespread confusion whenever Nat Geo, Discovery Channel or most websites talk about bite strength; they mix up bite force with bite pressure. If you take a plausible number for bite force and divide it by the area of the tip of a tooth to calculate pressure you get impressively large numbers that are just what producers and editors want as one-liners and click-bait. The next step is to convert the pressure back to force simply by repeating the number - and lo and behold a dog can lift a car with its teeth, hyaenas can cut steel bolts and sharks can crush unobtanium.

    Daisy chaining is worryingly common - nearly everyting on scenting dogs ultimately tracks back (pun, sorry !) to Syrotuck's "Scent and the Scenting Dog" which makes a lot of (entirely plausible) assertions on very little actual evidence, with no proper citations. A secondary problem of widespread recycling of flawed information is that everyone thinks the questions have been answered, so it is nearly impossible to get funding to look at them again.

  4. Dr. Brady Barr tested the bite strength of various animals for a National Geographic show back in 2005. (Dangerous Encounters: Bite Force 1&2) and among the animals tested was the common domestic dog... he tested 3 breeds: rottie, shepherd, and pit bull. for the dog's bite tests, he used bite-trained dogs and had them bite a sleeve with a sensor inside. of the 3 dogs tested, the pit bull turned in the lowest pressure at 235 psi. the rottie had the highest of the 3 with one bite at 265 and another at 328. a far cry from the 1600-2000 psi people attribute to pitties.


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