First of all define 'intelligence' as it applies to animals or even humans. Are you 'intelligent' enough to survive as a homeless person. If you don't atleast give me an idea where to look to find out please. If you answered NO to both you will clearly know of Dogs sniffing out illegal drugs and assisting blind people in their everyday lives. Humans are the most intelligent species on the planet, and if someone tried to get us to roll over and play dead, or go fetch a stick, most of us would raise an eyebrow and wonder if they were insane.
Cats are much more independent that dogs.
Also - notice that most dogs will bark a challenge at a stranger, while cats will usually keep a wary distance at first. Cats exhibit behaviors found in more intelligent species - dogs do not. The null hypothesis would be that dogs and cats are equal in intelligence. To perform the statistical test, you would take samples of dogs and cats and define some task, representing intelligence, for them to perform. From the data thus obtained, you would then statistically test your null hypothesis.