first of all, there are no statistics that prove that.
2nd, most of the time when you hear about a dog attack on the news, they say pit bull even if it isn't a pit bull. like everytime some white woman kills her kids, she says a black man kidnapped them. you'll hear, a pack of pit bulls ate some baby. well pits don't run in packs. also, somebody is less likely to report a poodle bite than a pit bull bite.
3rd, it's possible that a pit has a better chance of making you bleed on your pumas. but that's only because he has a stronger and bigger bite. that doesn't mean that the pit is more aggressive or more likely to attack. it's all how you raise the dog.
statistically speaking, pit bulls have a better temperament than beagles and golden retrievers.