This study used a survey, and there was no reported distinction made between registered and unregistered firearms.

The Harvard/Northeastern study is based on a survey of nearly 4,000 Americans conducted online in 2015 by a market research company, GfK, with a nationally representative panel of opt-in participants who are compensated to complete surveys on a variety of issues. The full results of the Harvard/Northeastern gun ownership study are undergoing peer review and are slated to be published in the autumn of 2017 by the Russell Sage Foundation. While the full peer review is not complete, lead researcher Azrael said, the current results have gone through an initial round of comments and revisions from a group of leading firearms researchers.