“every time a gun in the home was used in a self-defense or legally justifiable shooting, there were four unintentional shootings, seven criminal assaults or homicides, and 11 attempted or completed suicides.”
Well, the simple fact is, the police intentionally don’t keep data on the number of times a gun is presented to prevent a crime.
They may take a report if the weapon is fired, but they aren’t real interested in compiling data in that regard.
Since this study came from the "Journal of Trauma and Acute Care Surgery", I'm going to guess that they got their data from shootings that resulted in an ER visit. They count as self defense ONLY cases where the gun was (1) fired, AND (2) the bad guy was hit, AND (3) the case was immediately classified as self-defense.
Cases where the gun owner chased away the bad guy without wounding or killing the bad guy would not be counted as defensive shootings. Cases where the gun owner was initially arrested and the case was later decided as "self defense" would also not be counted.
An additional point: the vast majority of shootings involve inner-city criminals shooting other inner-city criminals, using guns they are legally prohibited from owning. A study which excluded those cases, and covered ONLY shootings where the gun owner was legally allowed to own the gun used, would paint a different story.