The people who bring in their dogs are a self selecting group, that is, only responsible owners of pitbull type dogs will bring in their animals for the test. Since the breeds under this category are known for being vicious creatures, people only bring in pits that they feel will pass the test. This is not the case for a border collie or a labrador. Since they're generally considered friendly, people will bring in their dog assuming it will pass the test regardless or, take it in because they suspect it has personality problems. If you had drug dealers bringing in their crack-guarding pits, I'd bet the results would be more around 00% or less.