Agreed. The approach we used in our earlier gun study and will also use in this study is to try and control for cultural differences across states using various

Agreed. The approach we used in our earlier gun study and will also use in this study is to try and control for cultural differences across states using various standard econometric techniques (fixed effects, lagged dependent variables etc). Otherwise it would be foolish to just eyeball Massachusetts and Mississippi and assume what works in one will work in the other!