I am attempting DID with having states from one year 1991 being compared to states from 1992 and so forth with the difference being the occurrence of a mass shooting with a possible difference appearing in the numberoflaws. I would like to capture the difference that occurs between states from one year to another and perhaps as a whole. The multiple same years keep giving me a error as well.
state string
year int
shooting byte
numberoflaws int

state year shooting numberoflaws
Alabama 1991 0 3
Alaska 1991 1 5
....
Alabama 1992 0 9
Alaska 1992 2 1
....
Alabama 1993 0 7
Alaska 1993 3 4
....