A Tale of Two Cities          Chicago , IL      Houston , TX   Population     2.7 million    2.15 million Median HH income   $38,600    $37,000  % African-American   32.9%    24%  % Hispanic   28.9%    44%  % Asian   5.5%    6%  % non-Hispanic White   31.7%    26%                          A reasonably similar matchup -until:       Chicago, IL    Houston, TX   Concealed carry gun law:        No    Yes  # of gun stores  0 84 dedicated gun shops and1,500 places to buy guns (Walmart, etc.) Homicides, 2012  506  207 Homicides per 100k  18.4 9.6   Average January high temp, F  31  63                    Conclusion: cold weather causes murder.