You may, or may not, be familiar with Arthur Kellerman. He was a medical doctor who wrote several pieces that were published in medical journals, such as the New England Journal of Medicine (similar research was presented in JAMA, and he may have been published there as well...I cannot recall), warning about the dangers of gun ownership. In brief, his research claimed to demonstrate that if you kept a gun in your home, you were multiple times more likely to be killed than use it in defense.
Critics found what they believed were problems with said research. For example, they said if you lived in a high crime neighborhood and owned a gun in response to the threat, and were subsequently killed by an intruder, your ownership of a gun was linked to your demise, even if the intruder killed you with a gun he brought into your residence. Critics believed correlation was confused with causation. Additionally, they reported no accounting for defensive gun use that didn't include killing an intruder (e.g. scaring off intruders by displaying the weapon, etc), a lack of controls for people who might be at higher likelihood of owning a gun and being murdered (drug dealers for example), and the list goes on and on. Studies like his were criticized by Kates, Kleck, Lott, Wright and Rossi, and others, but funded by tax-payers.