States were rated on how far their mental health reporting and background check requirements go beyond federal regulations. Level 1 shows little legislation and reporting beyond federal requirements. Laws on mental health reporting, universal background checks, and high frequency of submitting health records were used to gauge more protections. Level 2 states have one of those three factors, Level 3 states have two, and Level 4 has all three. More details available by state.
Sources: National Conference of State Legislatures, Law Center to Prevent Gun Violence, Everytown for Gun Safety, New York SAFE Act