Firearms ownership data is collected by the state, the state provides private gun ownership data to such researchers. Lots of opportunity to cherry pick desired outcomes when both data collector and researchers agenda merge.
GIGO.
Summary: 12 per 100k in handgun homes die from violence perpetrated with handguns while 8 per 100k in non registered gun homes die the same way.
Correlation (registered handgun home & number of deaths) does not mean causation.
Tell me how many people die in registered handgun homes from those registered handguns compared to how many die in non-registered handgun homes by violence from use of non-registered handguns as well as how many die from violence from use of registered handguns. Then tell me the rates of justified use of force for those categories.
That would be a meaningful resukt, but alas, it would tell a scary story that won’t be told.
Why should handguns be registered? Sounds like an infringement of the right to bear arms.