National Crime Victimization Survey (NCVS).
Data from the NCVS imply that each year there are only about 68,000 defensive uses of guns in connection with assaults and robberies,  or about 80,000 to 82,000 if one adds in uses linked with household burglaries.  These figures are less than one ninth of the estimates implied by the results of at least thirteen other surveys, summarized in Table 1, most of which have been previously reported.  The NCVS estimates imply that about 0.09 of 1% of U.S. households experience a defensive gun use (DGU) in any one year, compared to the Mauser survey's estimate of 3.79% of households over a five year period, or about 0.76% in any one year, assuming an even distribution over the five year period, and no repeat uses. 
The strongest evidence that a measurement is inaccurate is that it is inconsistent with many other independent measurements or observations of the same phenomenon; indeed, some would argue that this is ultimately the only way of knowing that a measurement is wrong. Therefore, one might suppose that the gross inconsistency of the NCVS-based estimates with all other known estimates, each derived from sources with no known flaws even remotely substantial enough to account for nine-to-one, or more, discrepancies, would be sufficient to persuade any serious scholar that the NCVS estimates are unreliable.
...The NCVS was not designed to estimate how often people resist crime using a gun. It was designed primarily to estimate national victimization levels; it incidentally happens to include a few self-protection questions which include response categories covering resistance with a gun.