A 2008 University of Pennsylvania study of 6,000 dog owners who were interviewed indicated that dogs of smaller breeds were more likely to be 'genetically predisposed towards aggressive behaviour'. Dachshunds were rated the most aggressive, with 20% having bitten strangers, as well as high rates of attacks on other dogs and their owners. The study noted that attacks by small dogs were unlikely to cause serious injuries and because of this were probably under-reported.
yes
yes