As a trainer who has actually studied and researched dog behavior, I had trouble reading this book. On several occasions I put it down in disgust, unable to read another word. But, because I want to be widely versed in dog behavior - even if it's just the inaccurate garbage that my clients might be exposed to - I did read it in its entirety. I have trouble citing anything from this book that is factual and would make it worth reading, apart from perhaps the entertaining historical anecdotes. If you want to know about dog intelligence, the dog behavior professional should read "Applied Dog Behavior and Training" by Lindsay (all 3 volumes) to start. For seriously interested dog owners and /or professionals, I recommend "Dog Behaviour, Evolution, and Cognition" by Ádám Miklósi. For lighter reading, Alexandra Horowitz's "Inside of a Dog: What Dogs See, Smell, and Know" is very good. Both the latter authors are doing research in the field of canine cognition, and so actually know a thing or two about the subject (unlike Coren).
The dog owner should understand that the "tests" in this book mean absolutely nothing and may actually be harmful by labeling a dog "dominant" or "aggressive" when he is nothing of the sort. Here are the main problems I found with Coren's book:
* Excessive reference to dominance theory, including the terms "alpha," "pack leader," etc. Dominance theory was created based on faulty research in the mid-20th century, which has since been updated and has been mostly thrown out when referring to pet dogs. Your pet dog is not a pack animal - if it were, it would kill every intruder to its territory, including the mail carrier, guests, and dogs that come to visit for "play dates." We could not live with a pack animal, and through the domestication process we have bred it out for our own convenience. Current research points to dogs as solitary animals, congregating in groups of 2-3 when food scarcity requires it. They are different enough from wolves that they simple can't be compared the way we used to think they could. Your dog does not jump up on you to establish dominance, nor as a sign of "disrespect." Humans are the ones obsessed with respect (or the lack of it), not dogs. Dogs know we are not dogs; they're not that stupid. And to assume that all dogs think about is social rank and dominance is simplifying their intelligence unnecessarily; most dogs could care less and have far better things to think about, such as how to get you to fill the food dish or pick up the leash. Coren likens dog intelligence to that of 2-year-olds, and yet doesn't make the connection that most dogs out there are trying to manipulate us - just like 2-year-olds - not dominate us.
*The "intelligence tests" themselves are not based on any sort of scientific research, nor was any research done to determine whether or not they are accurate. Simply reading them, I couldn't find a single test that I felt would be an accurate reflection of what they tested for. There were too many other ways - much easier, simpler, more reasonable ways - to interpret the results. For example, a dog that does not explore and show immediate interest in an environment that you have altered dramatically is given a low "score." However, a well socialized dog, used to seeing many different things and learning to take them all in stride, may show little or no interest - and you WANT that. Alternatively, if you're the type that rearranges the furniture often, the dog may be so used to it that he ignores the change. A dog that is quick to react and explore may well be neurotic, not intelligent. For another test, a dog is supposed to attempt to get a treat from beneath a towel. The author recommends using a biscuit. A dog, being an intelligent animal, may well decide that the effort involved in finding the biscuit is not worth the biscuit itself (being a very low-value food reward), thus scoring low on the test. A "spoiled" dog that is used to having problems solved for him will simply wait for you to retrieve the biscuit. I'd call these pretty intelligent dogs, personally. A dog that doesn't like his equipment (not uncommon if choke chains, prong collars, or the like are used) or that isn't walked on a leash often will fail test 1. A dog taught to "leave it," whether formally or informally, will fail test 2. Test 5 will likely be failed if you haven't taught your dog to hold eye contact, which is an unnatural behavior for dogs. In summary, some of the tests will insult your dog's intelligence, not test it. They are better used to show how much training your dog has received.
*The "personality tests" were simply ridiculous. Again, many of them test training, not personality, and they all are supposed to be able to gauge your dog's level of "dominance." Research has shown that the only personality factor that is worth testing in puppies is fear - all other factors tested were unrelated to dogs' adult personalities. Coren also suggests a puppy handling protocol that is actually different from that used by the US Army, and says "there is no harm in handling the pup for a longer period of time" than he suggests. This is false, harm can be done by over-handling of young puppies; it creates neurotic adult dogs.
*He refers to dog-human interactions in such cold terms that is debases the nature of the human-animal relationship. He described dogs "submitting to" the "commands" of their human "masters." Perhaps this is how he truly sees it, having been in the military and likely having a background in compulsion training. Luckily, training methods have evolved, and trainers have a better understanding of how learning and behavior occur. Dogs don't "obey" - they simply react the way that works best in a given situation. Humans, having a weakness for power and feeling important, sometimes interpret this as "obedience" and thus they think they have "control" over the dog. Nothing could be further from the truth. His attitude toward dogs and their behavior are a reflection of the type of training that was popular decades ago - current trainers with any sort of understanding of learning theory would never refer to dog behavior the way he does.
*He used obedience judges as "experts" in dog intelligence. Maybe it's just me, but somehow I think that someone who researches dog intelligence might be a better expert than someone who judges the effectiveness of a dog's training. (Let me note here that Coren does not research dog intelligence - his academic training has, in fact, nothing to do with dogs. He is a hobby judge and showman. He isn't an expert in dog intelligence - he just decided to write a book on it. I could write a book on the work Cohen did for his Ph.D., but that doesn't mean I'll have any idea what I'm talking about.) Obedience judges are trained to quantify how well a dog has been trained - not how easy or difficult it was to train any of them, taking into account the methods used and the experience of the trainer, the power of the reinforcers or punishers used, etc. His "experts" were poorly chosen. He says himself that he spoke to obedience judges because he found the idea of properly analyzing his data too daunting. I suppose it doesn't matter which he ended up doing, because he hadn't collected enough obedience trial data to yield accurate results, anyway, so either way his list of dogs by intelligence would be worth very little.
*His interpretation of dog body language is inaccurate, which must have been difficult to accomplish given the many good resources on dog body language. I recommend Turid Rugaas's book "On Talking Terms With Dogs: Calming Signals" and "Canine Behavior" by Barbara Handelman if this aspect of the book interested you.
In summary, this is a book written to be sold and create revenue, not to increase awareness of dogs or dog behavior. In fact, it does the opposite. It has a feature many find attractive - an intelligence test! Unfortunately, the tests do nothing of the sort. I'd hold off on trying to test your dog's intelligence until we figure out how to do it with people, which we currently aren't really sure how to do accurately. If you want to know how intelligent your dog is, ask yourself why it matters - every individual dog has something to offer, regardless of how "smart" or well-trained he is. Look for the things your dog is good at and emphasize those to bring the best out of him every day.